Electrojector and D-Jetronic: Early Electronic Fuel Injection


The first production electronic fuel injection system was the Bendix Electrojector, offered briefly by Chrysler for 1958. It was dropped due to unreliability, but it inspired Bosch to develop the similar but more successful D-Jetronic system, introduced by Volkswagen for 1968 (which required a patent licensing agreement between Bendix and Bosch) as a way of meeting U.S. emissions standards. In the seventies, both Chevrolet and Cadillac offered a second-generation Bendix electronic injection system, which was very similar to D-Jetronic and used some Bosch parts.

Once considered exotic technology, electronic fuel injection has been around a surprisingly long time. In this installment of Ate Up With Motor, we review the origins of EFI and examine the relationship between the pioneering Bendix Electrojector, Bosch D-Jetronic, and the second-generation Bendix system that introduced GM to electronic injection in the 1970s — a complicated web of technology, business, and politics.

Seville and "Fuel Injection" badges on the right front fender of a Naples Yellow 1977 Cadillac Seville sedan (Aaron Severson)


Please note that this is a history, NOT a repair or maintenance guide for fuel injection systems. I CANNOT to tell you how to repair Bosch D-Jetronic or Bendix fuel injection, and I CANNOT help you find parts! If you have maintenance, repair, or troubleshooting questions, please consult a qualified mechanic familiar with older fuel injection systems. (I am NOT a mechanic and am NOT qualified to give troubleshooting or repair advice.)

The Bendix Electrojector

Introduced in 1957, the short-lived Bendix “Electrojector” was the first commercially available electronic fuel injection system for passenger cars. It may be surprising to learn that the Electrojector was also one of the earliest production passenger car fuel injection systems of any kind, arriving right on the heels of the Rochester “Ramjet” continuous injection system offered by Chevrolet and Pontiac, and only about three years after the Mercedes-Benz 300SL became the first production car with a fuel-injected four-stroke gasoline engine. (It was preceded by a number of small fuel-injected two-stroke cars from Goliath and Gutbrod, introduced around 1951.)

B&W schematic of the Bendix Electrojector fuel injection system, showing the modulator and resistance box, secondary and primary throttle valve bodies, triggering selector, injector, intake manifold, fuel manifold, pressure regulator filter and vapor separator, fuel supply and return lines, fuel pump, and fuel tank (Inside Story - 02 - Stellantis Historical Services - rotated)

A 1958 diagram of the major components of the Bendix Electrojector system, reproduced from a special owner’s manual supplement entitled “The ‘Inside’ Story of Your New Electronic Fuel Injection System,” which was provided to Chrysler 300D buyers who opted for fuel injection. The booklet’s illustrations appear to have been repurposed from the Chrysler service training manual for the system, published in August 1957. (Image copyright Stellantis Historical Services)

There had been experiments with fuel injection going back to the 1890s, and it had been used with some success in aircraft engines, stationary applications, and race cars (and of course for diesel engines). However, passenger cars presented much greater challenges for fuel metering: A fuel injection system viable for street use needed auxiliary systems to provide for starting, engine warm-up, and idle, like a carburetor, and also needed to be able to maintain something close to a stoichiometric air/fuel ratio through a broad range of operating speeds, at part-throttle as well as full throttle, and respond immediately to changes in throttle position. Metering systems that were adequate for industrial or aircraft engines were simply not versatile or flexible enough for passenger car use on the street.

The Electrojector system had been in development since about 1951. It was the brainchild of Robert W. Sutton, assistant chief engineer of fuel systems engineering in the Bendix Eclipse Machine Division in Elmira, New York. Sutton was an aviation buff, and the injection system appears to have been at least in part a synthesis of certain recent developments in aircraft fuel systems, albeit intended to meet the far more complex metering needs of passenger cars. By 1953–1954, Bendix had a working prototype of this new system installed in a 1953 Buick for preliminary demonstrations to automakers, although the system — whose electronic control unit still used vacuum tubes until its fourth design iteration — was not yet ready for production. Nonetheless, Bendix found some auto industry interest, and in late 1956, American Motors Corporation (AMC) announced that the Electrojector system would shortly be an option on the new Rambler Rebel. In January 1957, Sutton and his boss, Albert H. Winkler, presented a paper on the new system at the annual meeting of the Society of Automotive Engineers (SAE) in Detroit.

1957 Rambler Rebel front 3q, a silver four-door hardtop with gold side trim (Christopher Ziemnowicz)

Had American Motors Corporation not gotten cold feet at the last minute, the 1957 Rambler Rebel would likely have been the first U.S. production car to use electronic fuel injection. AMC announced in late 1956 that the option would be available on the Rebel, but by the spring of 1957, they had dropped plans to offer the Bendix injection system. Company officials didn’t say why, although some privately told automotive journalists that the Electrojector system required too many engine changes and had unresolved problems with cold starts. (Photo: “1957 Rambler Rebel hardtop rfd-Cecil’10” by CZmarlin — Christopher Ziemnowicz; released to the public domain by the photographer)

Like the Rochester Ramjet or the later Bosch mechanical systems, the Electrojector was a port injection system, delivering fuel through separate injectors mounted just above each intake valve (rather than into the combustion chamber as with the diesel-derived Bosch gasoline direct injection system on the 300SL). Unlike the Rochester system, the Electrojector was intermittent, delivering fuel to each cylinder in timed pulses. Fuel for the injectors was supplied by a common fuel rail, which an electric fuel pump maintained at a constant pressure. The amount of fuel delivered to the intake port therefore depended on how long each injector valve remained open. Since the injector valves were controlled by solenoids, the open time of each valve and the duration of each fuel pulse depended on the pulse width of the electrical signal that energized the solenoid, also known as the pulse duration and usually measured in milliseconds. This duration was proportional to the total resistance in the circuit, which could be varied based on different control inputs.

B&W schematic of the Bendix Electrojector injector control system, showing the modulator, resistance box, triggering selector, injector, fuel manifold, and intake passage (Inside Story - 06 (4) - Stellantis Historical Services)

As this schematic from the Chrysler 300D owner’s manual supplement shows, the Bendix Electrojector system mounted its various resistors (which determined the pulse duration of the injection pulses based on sensor inputs) in a separate box with a heavily perforated cover so that the heat the resistors generated wouldn’t cook the circuitry in the electronic control unit (modulator) itself. (Image copyright Stellantis Historical Services)

The idea of electronically controlled injector valves wasn’t a new idea even in the mid-fifties. Back in the early thirties, California engineers Harry E. Kennedy and Brooks Walker had devised a similar electronically controlled injection system with magnetically operated port injection valves, intended as part of an ambitious but somewhat half-baked scheme to allow spark ignition engines to run on cheaper diesel fuel. The Atlas Imperial Diesel Engine Co. (Atlasco) of Oakland, California, installed this system, which also included a high-tension arc ignition system and an alternator rather than a generator, on marine and truck engines, but it never went into mass production, probably for reasons of cost as much as reliability concerns. A few years later, Milanese engineer Ottavio Fuscaldo, then working in the experimental department of the Italian aircraft company Caproni, developed a similar electronic system, adaptable for either port or direct injection. The Caproni-Fuscaldo system was installed on an Alfa Romeo 6C 2500 that ran in the 1940 Mille Miglia, and was at least considered for aircraft applications, although we don’t know if it ever actually saw any aviation use. It would have needed considerably more development make it suitable for passenger car duty, but the basic principle was the same as the Electrojector and subsequent timed electronic injection systems. One of Fuscaldo’s patents (U.S. Patent No. 2,332,909) is among the references cited in the core Bendix electronic fuel injection patent (U.S. Patent No. 2,980,090).

B&W patent illustration showing a simplified schematic of an electronic fuel injection system with major components identified by numbers (US2332909, Fig. 1)

Twenty years before the Electrojector, Caproni engineer Ottavio Fuscaldo’s electronic injection system used one injector (1, left) per cylinder, injecting into either the port or the combustion chamber, controlled by a valve (6) opened or closed by a solenoid (13, in casing 11). A fuel rail (5) under constant pressure supplied fuel to each injector through pipes (19), so the amount of fuel injected was determined by how long the solenoid remained energized, which was controlled by an engine-driven commutator (4). (Illustration: Fig. 1 of U.S. Patent No. 2,332,909, “Fuel Injection Valve Apparatus,” Ottavio Fuscaldo, application 14 April 1937 (based on an Italian patent application filed 18 April 1936), divided 16 March 1940, patented 26 October 1943)

Like the Atlasco and Caproni-Fuscaldo systems, the Electrojector initiated each fuel delivery pulse using what Bendix called a triggering selector, essentially an additional set of distributor breaker points. Depending on the application, the triggering selector could either be incorporated into the ignition distributor as an additional “sandwich” section or else carried in its own housing, driven by gears off the distributor shaft and rotating with it at one-half engine speed. The triggering selector acted as a mechanical speed sensor, and also made it possible to time the injection pulses to coincide with the engine’s combustion cycle, delivering fuel during the intake stroke of each cylinder.

Each time the triggering selector breaker points opened, they sent a spike signal to a multivibrator circuit in the transistorized electronic control unit (ECU), also known as the modulator. The modulator transformed this spike signal into a square pulse, whose duration varied with the resistance in two control circuits connected to the system’s various sensors. The ECU then sent the modified pulse back to a distribution commutator in the triggering selector, which would energize each injector at the appropriate time, with the pulse width determining how long the injector remained energized.

There were two control circuits, also called sensor circuits: the main control circuit, which had an intake manifold pressure sensor and an acceleration sensor switch, and an auxiliary control circuit with sensors for cold start and warm-up, idle enrichment, and intake air temperature, plus a de-loading device for cranking on wide open throttle in the event of a flooded engine. There was also an altitude compensator in the ECU that adjusted the modified pulse width to compensate for variations in barometric pressure. All of these sensors were purely analog. For example, the manifold pressure sensor was a potentiometer controlled by a crank and a spring-loaded piston that reciprocated in a cylinder open to manifold pressure. (Sufficiently high manifold vacuum would also cut off fuel flow during deceleration or overrun.)

B&W patent illustration showing a cutaway schematic of the manifold pressure sensor for the Bendix Electrojector electronic fuel injection system, with major components identified by numbers (US2900967, Fig. 6)

The Electrojector manifold pressure sensor used a spring-loaded piston (142) reciprocating in a cylinder (50) with a port open to manifold vacuum (52, lower left). Changes in manifold vacuum would move the piston back and forth, rotating the crank arm of the potentiometer (146) and thereby increasing or decreasing the resistance in the primary control circuit. The rounded cap on the right, not labeled, houses a heating coil that actuates the fast-idle cam (42) until the engine reaches normal operating temperature. The production version of this sensor, shown in the schematic below, differed a little in appearance, but functioned in the same way. (Illustration: Fig. 6 of U.S. Patent No. 2,900,967, “Fuel Supply System,” Robert W. Sutton (assignor to Bendix Aviation Corporation), application 11 March 1957, patented 25 August 1959)

The Electrojector used speed-density metering: Engine speed, signaled by the triggering selector, determined the frequency of injection pulses, while manifold pressure determined the basic pulse width, and thus how much fuel each pulse delivere. Auxiliary sensors triggered additional enrichment (i.e., increased pulse width) under certain operating conditions. All that sounds very impressive — indeed, it wasn’t until the early eighties that pundits and automotive journalists overcame their awe at the Hugo Gernsback wonders of the electronic “brain box” — but mechanical fuel injection systems for passenger car applications necessarily incorporated all or most of the same types of sensors, for the same purposes, even if they performed their metering calculations with vacuum signals or the motion of cams and levers rather than with electrical pulses.

B&W photo of the primary throttle valve body of the Bendix Electrojector fuel injection system, with call-out lines to illustrations of the sensors: the acceleration sensor, idle sensor, manifold vacuum sensor, and cold start and warm-up sensor (Inside Story - 10 (8) - Stellantis Historical Services)

Although Chrysler cars with the Bendix Electrojector system had dual throttle bodies, most of the sensors were fitted to the primary throttle body, as shown in this illustration from the 1958 owner’s manual supplement. The exception was the altitude compensator, which was located inside the modulator box and adjusted the injection pulse width after the other sensor inputs. This didn’t work very well, although an improved altitude sensor designed by Bendix engineer Stephen G. Woodward (U.S. Patent No. 3,159,151) never made it to production. (Image copyright Stellantis Historical Services)

Ironically, one of the big selling points for the Electrojector was that it promised to be cheaper than mechanical fuel injection systems. As Winkler and Sutton explained in their 1957 SAE paper, the Electrojector operated at much lower pressures than mechanical injection systems, needed no power-consuming pump drive, had fewer moving parts, didn’t demand costly precision machining, and had less critical fuel filtration requirements. Some of the anticipated cost advantages presumed greater production volumes and improvements in electronics manufacture that didn’t materialize until decades later, but if you compare the relatively unstressed mechanical components of the Electrojector with the daunting complexity and enormous cost of the diesel-derived Bosch six-piston jerk pump used on the Mercedes-Benz M198 engine — which had to precisely meter very small quantities of fuel while withstanding fuel rail pressures up to 1,700 psi (117 bar) and injection pressures of up to 682 psi (47 bar) — the idea that the Bendix system might eventually be cheaper to manufacture doesn’t seem altogether far-fetched.

Indeed, when AMC announced the Electrojector as an option for the 1957 Rambler Rebel, the quoted retail price was $395 — a lot of money in 1957, but a substantial $89 cheaper than the Rochester mechanical system on a ’57 Chevrolet. AMC canceled the fuel injection option option before it actually went on sale, but in late September, Chrysler announced that it would offer the Electrojector on its hottest 1958 Chrysler, Dodge, DeSoto, and Plymouth models. List price was $400, still cheaper than Chevrolet or Pontiac charged for the Rochester unit. Whether the Bendix system would have retained any price advantage had both systems reached large-scale production is hard to say, but the Electrojector initially appeared competitive from a cost standpoint.

Bendix claimed that on a “typical” V-8 engine, the Electrojector offered more power, more torque, and better fuel economy than a four-barrel carburetor across the entire operating regime; eliminated hesitation on abrupt throttle changes; and provided excellent starting and warm-up performance. AMC announced that the 327 cu. in. (5,354 cc) V-8 in the 1957 Rambler Rebel would produce 288 hp (214.8 kW) and 350 lb-ft (475.6 N-m) of torque, 33 hp (24.6 kW) more than the carbureted version. Chrysler quoted a more modest 10 hp (7.4 kW) advantage for Electrojector-equipped cars, although as we’ll see, this rating was largely speculative.

1957 Rambler Rebel engine compartment, showing the carbureted 327 cu. in. (5,354 cc) V-8 engine (Christopher Ziemnowicz)

Even without the troublesome Bendix Electrojector system, the new four-barrel version of the AMC 327 cu. in. (5,354 cc) V-8 had a respectable 255 gross horsepower (190.2 kW) and 345 lb-ft (468.8 N-m) of torque, giving the 1957 Rambler Rebel impressive acceleration for its era. The injected version allegedly boasted 288 hp (214.8 kW), although the increase in torque was a mere 5 lb-ft (6.8 N-m) over the carbureted engine. (Photo: “1957 Rambler Rebel hardtop eng-Cecil’10” by CZmarlin — Christopher Ziemnowicz; released to the public domain by the photographer)

Like any fuel injection system, the Electrojector offered a number of potential performance advantages (like facilitating the use of tuned intake runners for resonance supercharging, as Mercedes did on the 300SL), but achieving that potential required more substantial engine changes than Chrysler (or apparently AMC) was prepared to make. In fact, the Chrysler cars equipped with fuel injection were assembled with carbureted engines and then taken to the DeSoto plant, which removed the carburetors and installed the Electrojector system. Consequently, the main performance benefit was a small power increase due to the elimination of the manifold heat riser, which a port injection system didn’t need.

Chrysler Engineering Excoriates the Electrojector

Although it sounded great on paper, the Bendix Electrojector system was an almost unmitigated disaster in execution. We haven’t seen any AMC engineering evaluations — AMC didn’t officially comment on its reasons for abandoning the Electrojector option — but surviving Chrysler Engineering documents paint a very grim picture of the system’s problems and design flaws.

The most immediate of these was the grievous unreliability of the solenoid-activated injectors. In principle, the injectors offered very precise control of fuel delivery, but in practice, fuel flow was so wildly inconsistent that Chrysler test engineers were never able to obtain actual gross or net power and torque ratings for the injected engines. Early injector valves were too slow to open and much too slow to close, which meant that the actual effective duration of each fuel pulse could be several times the calculated value. Injector leakage also caused excessive fuel consumption at cruising speeds, and in at least a few cases dumped liquid fuel into the cylinders, which could have engine-ruining consequences as well as presenting a potential fire hazard. Chrysler engineers had to completely redesign the injector valves and divide the ECU’s multivibrator circuit into two separate channels before the injectors would open and close with anything approaching the necessary speed. Even then, injector fuel flow variation remained about twice that of contemporary carburetors — ±6 percent versus ±3 percent — and obtaining any semblance of consistent fuel distribution required installing or replacing the injectors in carefully matched sets.

B&W cutaway illustration of the Bendix Electrojector injector assembly, showing the fuel inlet, filter screen, lockring, coil, star spring, disc valve, and discharge orifices (Inside Story - 07 (5) - Stellantis Historical Services)

This image from the 1958 owner’s manual supplement shows the inner workings of the Bendix Electrojector injector valve. Although the principle is simple — the injector is essentially just a spring-loaded plunger, held open magnetically when the coil is energized — Chrysler Engineering struggled to get the injector valves to close quickly enough for proper metering. As a withering October 1959 report explains, early injectors from Bendix needed around 9 ms to close, which was about 10 times as long as intended, and much longer than the average injection pulse width, which was only in the range of 1.0 to 4.3 ms! (Image copyright Stellantis Historical Services)

Another issue affecting fuel consumption was high evaporative losses. Today, cars have evaporative canisters that capture fuel vapor so that it can later condense and return to the fuel tank, but in the late fifties, evaporative emissions were simply vented to the atmosphere. Because the Electrojector was constantly returning excess fuel from the pressurized fuel rail to the tank, Chrysler found that injected cars lost significantly more fuel to evaporation than did carbureted cars.

Driveability of Electrojector-equipped cars was further marred by cold starting problems and by the fact that the system’s capacity for acceleration enrichment was very limited. The acceleration sensor was a vacuum diaphragm switch responsive to manifold vacuum, positioned in series between the power supply and the manifold pressure sensor, which when open would increase resistance on the primary control circuit, increasing injection pulse width. This worked only in hard acceleration, was only momentarily effective, and could not vary the amount of enrichment based on operating conditions. Bendix explored other acceleration enrichment systems with more progressive action, but they weren’t used on the production Electrojector.

Patent illustration showing a cutaway of the acceleration switch for the Bendix Electrojector electronic fuel injection system, with major components identified by numbers (US3106196, Fig. 2 - color added)

The Electrojector acceleration switch (114, highlighted in green) was normally closed, allowing current to flow from lead 112 to lead 114, with no substantive increase in resistance. A sudden change in intake vacuum (signaled through port 78, lower right) would create a pressure difference between the sides of the diaphragm (64), causing the diaphragm to shift upward, compressing the spring (76) and opening the switch. This caused current to flow through an additional resistor between the leads (not shown), increasing injection pulse width. A bleed hole (70, highlighted in fuchsia) would quickly equalize pressure around the diaphragm, and the spring would then force the switch back into the closed position. (The production version, shown in the schematic above, looks a little different, with the bleed hole adjacent to the vacuum port, but functions the same way.) The earliest Bosch D-Jetronic systems used a similar mechanism, which Bosch called a pressure switch. (Illustration: Fig. 2 of U.S. Patent No. 3,106,196, “Fuel Supply System,” Stephen G. Woodward and Curtis A. Hartman (assignors to The Bendix Corporation), application 16 November 1956, patented 8 October 1963; color highlights added by the author)

On top of that, for reasons Chrysler was never able to determine or correct, the ECU suffered output decay at higher engine speeds: At speeds over 4,000 rpm, fuel delivery would fall off when it should have been increasing, causing the engine to run lean. The only way Chrysler engineers found to compensate for it left the engine running too rich at lower speeds, further exacerbating the system’s excessive fuel consumption.

The Chrysler documents we’ve seen make no mention of the oft-repeated contention that the Electrojector system was susceptible to interference from outside radio sources, and after examining the system’s wiring diagrams, Chrysler 300 Club member John Grady, an electrical engineer, dismissed those anecdotes as very unlikely. However, Grady felt that the lifespan of the trigger contacts in the distribution commutator was likely very short, and noted a distinct lack of voltage regulation. Some other reports indicate that the system’s waxed paper capacitors would “drift” over time and could eventually fail completely in hot, humid conditions (something that may not have come up in Chrysler engineering tests, but was potentially very troublesome for owners in warm climates).

1958 Chrysler 300D right front 3q, an Ermine White two-door hardtop (Cars Down Under)

With its dramatic “FlightSweep” styling, stiff suspension, and 392 cu. in. (6,425 cc) FirePower V-8 (with solid lifters and rather racy valve timing), the Chrysler 300D was the ultimate exemplar of the model’s original “banker’s hot rod” mission, selling in limited numbers to well-heeled buyers like (according to Chrysler PR) ranchers, oil tycoons, and pro athletes. Between 16 and 35 of those customers paid an extra $400 for the Bendix Electrojector system, a decision they soon came to regret — most cars were eventually retrofitted with dual four-barrel carburetors, which is also how the injected cars were originally assembled. (Photo: “1958 Chrysler 300D Hardtop” by Cars Down Under, which is licensed under a Creative Commons Attribution 2.0 Generic (CC BY 2.0) license)

Interestingly, Chrysler engineers found that timing each injection pulse to correspond with the opening of the intake valve, was an unnecessary complication. Such cyclic timing was important with direct injection, but with port injection, it made little difference whether the intake valve was opened or closed when fuel was delivered to the port.

To make a long story short, the Electrojector system was oversold and grossly underdeveloped. The Rochester Ramjet system was also finicky, especially early examples, but the Chrysler reports make clear that the Electrojector as it existed in 1957–1958 should never have been released to actual customers. AMC apparently reached that conclusion early on, but Chrysler buyers were not so fortunate, although Electrojector sales were few.

Exactly how many systems were sold is unclear. Automotive journalist Karl Ludvigsen later reported that AMC bought about 50 Electrojector systems and Chrysler about 300 (a figure that Bendix project engineer Jerome G. Rivard repeated in a 1974 SAE paper on the development of electronic injection), but those totals appear to reflect preliminary orders rather than actual deliveries.

1958 Plymouth Fury hardtop right front 3q, a B&W press photo (Stellantis Historical Services)

Introduced in 1956, the Plymouth Fury was originally a high-performance model and the top of the Plymouth line, until 1959 available only as a two-door hardtop. The 1958 edition had quad headlights and the option of a 350 cu. in. (5,735 cc) Golden Commando engine, making 305 gross hp (227.4 kW) in carbureted form. The Bendix Electrojector system was optional on the Golden Commando engine, but only two cars were so equipped. (Photo copyright Stellantis Historical Services)

AMC installed a few Electrojector units in engineering test or preproduction cars, perhaps as many as six. It doesn’t appear that any cars so equipped were actually sold to customers, although at least one may have eventually ended up in the hands of a private owner. As for Chrysler, the engineering report indicates that production changes that were slated to take effect with the 85th system were canceled in May 1958 because Chrysler had decided not to order that many. Since some early systems were likely reserved for testing and service replacement purposes, the number installed in production cars was undoubtedly lower still. Comments by the superintendent of the DeSoto plant that installed the system indicate that the Electrojector went into 54 cars in early 1958, although the actual total may have been as few as 35. Almost all later had their injection systems replaced with dual four-barrel carburetors by dealer service departments; it doesn’t appear that there was a formal factory recall to remove the Electrojector equipment, but the division service groups were authorized to do so in response to repeated owner complaints. Very few cars survived with their original injection systems intact.

Chrysler Engineering eventually recommended against further fuel injection development, either of the Bendix system or of an in-house system, originally developed in 1956 and shelved following the decision to adopt the Electrojector. (The in-house designs, developed under the A-632 and A-664 programs, were mechanical, not electronic — low-pressure continuous injection systems.)

Fuel Injection Limbo

Bendix engineers kept tinkering with the Electrojector design on a limited basis through at least 1962, and some related patents (most of which had been filed in 1956–1957) weren’t issued until as late as 1964. However, while the system still had a few internal champions — some of whom subsequently left to start their own company, Conelec, which tried to develop its own aftermarket electronic fuel injection conversion kit — Bendix corporate enthusiasm had largely dissipated. The project had already been very expensive, and there were still many issues to iron out before it would be reliable enough for real-world use. Worse, the calamitous service record of the early Electrojector units had only validated Detroit’s contemporary mistrust of electronic gadgetry, and it seems likely that Bendix had burned some bridges, especially at Chrysler and AMC.

Ironically, by the early sixties, Bendix had managed to secure worldwide patents covering many fundamental aspects of electronically controlled fuel injection systems. This meant that Bendix now enjoyed a near-monopoly on an immature technology the corporation had lost interest in pursuing, and had already mishandled so badly as to nearly scupper its commercial potential. If this wasn’t the worst-case scenario from the standpoint of technological development, it wasn’t far from it. Bendix may have pioneered electronic fuel injection, but the Electrojector had also come close to digging the concept’s grave.

1959 Mercedes-Benz W189 300d front 3q, two-tone gray over dark blue (Berthold Werner)

Introduced for 1958, the Mercedes-Benz 300d (W189) was the first four-stroke production car with Bosch mechanical port fuel injection — the 300SL and 300S/300Sc system injected fuel directly into the combustion chambers, which worked well in high-speed driving, but made cold starts troublesome and tended to contaminate the engine oil with gasoline, hardly suitable for a sedan of this class. In 1959, Bosch used a Mercedes 300 to test an early electronic fuel injection system. (Photo: “Mercedes Benz W189 BW 1” by Berthold Werner, which is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported (CC BY-SA 3.0) license)

In any event, passenger car fuel injection was now looking like a fad whose time had passed. For a little while in 1956–1957, it had seemed like the next big thing, but the late fifties recession, the Automobile Manufacturers Association racing “ban,” and the decision of NASCAR and USAC officials to prohibit fuel injection after the 1957 season had sapped much of the early momentum, leading most automakers to conclude that fuel injection cost too much for too little benefit. The Rochester system remained an expensive Corvette option through 1965, and mechanical fuel injection was still offered on some high-end European cars, but the auto industry had otherwise concluded that fuel injection, electronic or mechanical, cost too much for too little benefit.

Electronic Fuel Injection at Bosch

During this time, the engineers at Robert Bosch GmbH in Stuttgart had not been idle. Bosch had produced the mechanical gasoline direct injection system for the M198 engine in the 300SL, and subsequently developed mechanical port injection systems for the W186 Mercedes-Benz 300d, introduced in August 1957, and the W111 220SE, introduced a year later, but Bosch engineers had also been working on electronically controlled gasoline injection (ECGI) since 1956. Richard Zechnall, director of development for automotive lighting, ignition, and electronic controls, had established an ECGI project team in the automotive electronics advanced development department in January 1957, around the same time Winkler and Sutton presented their paper on the Electrojector system to the SAE. By 1958, engineers Hermann Knapp and Hubert Schäfer had designed a solenoid-controlled valve, and in October 1959, Knapp and Günther Baumann had applied for patents on a complete electronic injection system, with metering based on engine speed and throttle position.

B&W Bosch internal diagram of a constant-pressure electronic fuel injection system for a six-cylinder engine (Robert Bosch GmbH, Prinzipschaltbild elektronische Benzineinspritzung BEW-022 SK32)

This diagram, dated 30 January 1959, depicts an early Bosch electronic injection system, possibly the same one subsequently patented by engineers Günter Baumann and Heinrich Knapp (as Deutsches Patentamt Auslegeschrift 1,121,407 and U.S. Patent 3,005,447), with triggering contacts in the ignition distributor and a throttle-controlled potentiometer as the primary control variable and provision for additional electronic controls for cold start (Kaltstart), warm-up (Warmlauf), altitude correction (Höhenkorrektur), and intake air temperature (Ansaug-Lufttemperatur). (Diagram copyright Robert Bosch GmbH, Corporate Archives)

By the time those patents were filed, the initial layout already been superseded by a revised ECGI design using speed-density metering based on manifold absolute pressure, which was installed in a test car in the fall of 1959. Between 1962 and 1964, the advanced development department installed prototype systems in two test cars, a Volkswagen Type 3 and a W111 Mercedes 220SE, for demonstration to prospective customers. However, according to Hermann Scholl, who had joined the team in 1962 and subsequently became the project’s chief engineer, French and German automakers showed little serious interest, skeptical about the idea of electronic controls.

1963 to 1965 Mercedes-Benz W111 220 SE front 3q, a red sedan with matching wheel trims (Spielvogel)

Introduced for 1959, the 220SE version of the Mercedes-Benz W111 had a new lower-pressure Bosch mechanical fuel injection system with a two-piston metering pump, which gave the 133.9 cu. in. (2,195 cc) M127 six a respectable 120 PS DIN (88.3 kW), 134 gross horsepower (99.9 kW). A 220SE was one of two cars used as demonstrators for the prototype Bosch electronically controlled gasoline injection system between 1962 and 1964. (Photo: “Mercedes 220 SE . Spielvogel” by Spielvogel, which was dedicated to the public domain by the photographer under a CC0 1.0 Universal (CC0 1.0) Public Domain Dedication; it was previously recropped in 2023 by Heierlon)

Less than two months after Bosch demonstrated the system to Volkswagen officials in May 1964, a new variable entered the equation: exhaust emissions requirements for passenger cars. In the interests of public health, California had already laid the legislative groundwork for state standards regulating automobile crankcase and tailpipe emissions, aiming for substantial reductions in smog-producing emissions by 1970. However, the law had been structured to delay enactment of the tailpipe emissions requirements until after the state’s Motor Vehicle Pollution Control Board had approved at least two suitable emission control devices. At its meeting on June 17, 1964, the board approved four such devices, which meant that beginning in the 1966 model year, all new cars sold in California would be required to use approved exhaust emissions controls capable of reducing unburned hydrocarbon emissions to no more than 275 parts per million (ppm) and carbon monoxide emissions to no more than 1.5 percent of total exhaust volume, about one-third the emissions of an uncontrolled engine. These limits would be enforced by the California Highway Patrol in roadside inspections, using standardized testing procedures: the first iteration of what are now known as “smog checks.” (Impromptu roadside inspections were discontinued in 1975, to the great relief of motorists, although most cars registered in California must still complete periodic smog certification, typically every other year.)

B&W photo of a model showing the components of the initial Bosch D-Jetronic system, labeled "Elektronische Benzineinspritzung" (Robert Bosch GmbH, Corporate Archives)

Major components of the Bosch electronically controlled gasoline injection system (Elektronische Benzineinspritzung as used in the U.S.-market 1968 Volkswagen 1600. Top row, left to right: fuel pump (Krafstoffpumpe, pump, and fuel pressure regulator (Druck-regler), with the fuel rail between the pump and the regulator feeding the four injectors. Second row, left to right: ignition distributor (Zünd-verteiler), cylinders with individual solenoid-controlled valves (not labeled), auxiliary air device (Zusatz-luft-schieber), temperature sensor (Temperaturfühler), pressure sensor (Druckfühler), pressure switch (Druck-schalter) for acceleration enrichment, and throttle-valve switch (Drosselklappenschalter). Bottom row: control unit (Steuergerät) and battery. Note that the system lacks a cold-start valve, which was added a year or so into production. (Photo copyright Robert Bosch GmbH, Corporate Archives)

The California standards posed a very serious problem for Volkswagen, which was then preparing to officially introduce its Type 3 models in the U.S. for the 1966 model year. Most of the available emissions control devices imposed significant performance penalties even on big V-8 engines, much less an engine with only 65 gross horsepower (48.4 kW), and many such devices were not readily compatible with the Type 3 cars’ air-cooled flat four. California officials, acknowledging that emissions control devices designed for larger engines might not be suitable for smaller ones, allowed manufacturers to delay compliance of engines displacing less than 140 cu. in. (2,300 cc) for an additional two years, but this was only a temporary reprieve, not a permanent exemption. Volkswagen would have to make the Type 3 compliant with California emissions standards by December 1967 or else withdraw the model from one of its largest and most important export markets.

Bosch suggested that with electronic fuel injection, it would be possible for the Type 3 engine to meet the California standards through more precise air/fuel metering, without the need for power-sapping smog-control ancillaries. Volkswagen management, deeply conservative in that period, was wary, but management board member Helmut Orlich persuaded Volkswagen officials to assign some research and development engineers to work with Bosch on developing an emissions-compliant ECGI system for the 97 cu. in. (1,584 cc) four used in the Type 3 and forthcoming Type 4. By June 1965, Volkswagen determined that the system was sufficiently well-developed for production, and decided to make electronic fuel injection standard equipment on all U.S. Type 3 models for the 1968 model year.

Title page of the Federal Register, Volume 31, Number 61, Wednesday, March 30, 1966, Washington, D.C. Part II: Department of Health, Education, and Welfare, "Control of Air Pollution From New Motor Vehicles and New Motor Vehicle Engines" (No. 61—Pt. II—1), with an illustration of the National Archives building and the seal of the National Archives of the United States, 1934.

The publication that put into effect the first U.S. federal emissions standards, effective beginning with the 1968 model year. These regulations were originally codified at 45 CFR Part 85, but since the Department of Health, Education, and Welfare has since been divided into separate departments, the modern versions of these regulations are now at 40 CFR Part 86. (Image: Extract from the Federal Register for 30 March 1966, believed to be in the public domain in the United States)

This proved to be a prescient move. Throughout this period, the U.S. Congress had been debating whether to amend the Clean Air Act to establish nationwide standards for automobile emissions. On October 20, 1965, President Lyndon Johnson signed Senate Bill 36, the Motor Vehicle Air Pollution Control Act (subsequently Public Law 89-272), which provided the statutory basis for the first federal emissions regulations, enacted on March 30, 1966. These standards, modeled on but not identical to those of California, applied to all new gasoline engines and gasoline-powered motor vehicles with engines larger than 50 cu. in. (820 cc), beginning with the 1968 model year. The question of whether the federal rules would preempt California’s had not yet been settled (a complex matter beyond the scope of this article), but Volkswagen prudently assumed it would shortly need to comply with both federal and California standards.

In the fall of 1965, Bosch quintupled the size of its advanced development department and built 40 ECGI prototypes for testing and evaluation, including verifying that the system did indeed comply with California emissions standards. Bosch also began establishing the manufacturing capacity to build the systems in the quantities Volkswagen needed, which amounted to some 10,000 units per month. Since Bosch had little production experience with complex electronics, initial ECU production was contracted to the audio company Blaupunkt, a Bosch subsidiary. Testing concluded in spring 1967 and Volkswagen placed its first production order in June.

1968 Volkswagen 1600 TL front 3q, a press photo of a Peru Green fastback with an image of the Bosch D-Jetronic control unit superimposed over it (Robert Bosch GmbH, Corporate Archives, VW 1600 TLE Typ 3 und Bosch D-Jetronic Steuergerät1967)

Bosch D-Jetronic fuel injection was standard on all U.S.-bound Type 3 Volkswagen models beginning in 1968, and was standard on the later Type 4 as well. The injected engine offered no additional power — output remained 65 gross horsepower (48.5 kW) — but enabled the Volkswagen 1600 to comply with California and federal emissions standards without sacrificing any of its already modest performance. (Photo copyright Robert Bosch GmbH, Corporate Archives)

Bosch announced the new ECGI system, designated “D-Jetronic,” at the International Auto Exhibition (IAA) in Frankfurt in September 1967. That fall, the first Volkswagen 1600 models with D-Jetronic went on sale in the U.S. Volkswagen subsequently offered the injected as an option on the German-market Type 3, beginning in June 1968, but since there were as yet no local emissions standards requiring it and the system added about 10 percent to the total price of the car, home market sales were poor.

Reliability was not a strong point of the early D-Jetronic systems, due in large part to the sheer complexity of the electronic control unit. Like Bendix, Bosch also suffered early problems with the solenoid-controlled injector valves and with cold starting, with the latter requiring some early design changes. Still, with even stricter exhaust emissions standards emerging in the U.S., there was now considerable interest among European automakers, including Mercedes-Benz, Volvo, Opel, Citroën, SAAB, BMW, Lancia, and Aston Martin, among others.

Color photo of an early Bosch D-Jetronic electronic control unit surrounded by other fuel injection components (Robert Bosch GmbH, Corporate Archives, 1967 1-CR-21461-1)

With more than 250 separate components, including around 30 transistors, the D-Jetronic electronic control unit was complex — and often the system’s weakest link from the standpoint of reliability. The ECU had two separate circuit boards, a main board that was largely the same across different engine applications, and an auxiliary board with application-specific circuitry. (Photo copyright Robert Bosch GmbH, Corporate Archives)

By 1970, Bosch had developed D-Jetronic systems for four-, six-, and eight-cylinder engines; brought ECU production in-house; established sufficient capacity to manufacture 1.8 million injectors per year; and broken ground on its own semiconductor factory in Reutlingen, which went online in 1971. Bosch was selling more than 300,000 D-Jetronic systems per year in Europe, and subsequently signed license agreements with the Japanese firms Nippon Denso (part of the Toyota Group), Diesel Kiki (part of the Nissan Group, but also an Isuzu supplier), and MELCO (part of the Mitsubishi Group), followed later by England’s Joseph Lucas Ltd.

Bendix and Bosch

Although neither Volkswagen nor Bosch made any mention of it at the time, it was common knowledge among many American automotive journalists of the time, including John R. Bond, Jan P. Norbye, and Karl Ludvigsen, that the Bosch system involved Bendix patents related to the old Electrojector system.

Norbye’s account, which has been repeated as fact in various subsequent sources, suggests that Bendix had “perfected” the Electrojector by 1965, but then elected to license it to Bosch rather than put it back into production. However, in an article in the March 1968 issue of Motor Trend, Karl Ludvigsen (whom we’re inclined to regard as generally more credible than Norbye) instead asserted that the new system was strictly a Bosch design, but that Bendix had such extensive patent coverage in this field that Bosch “had to draw heavily on the very comprehensive Bendix f.i. patents.” Judging by the patents in question, this seems plausible: The core Electrojector patent alone (U.S. Patent No. 2,980,090) included 39 claims, some of them extremely broad, and Bendix had obtained patent protection in West Germany (principally under Deutsches Patentamt Auslegeschrift 1,100,377) as well as in the United States, France, and Great Britain.

Excerpt of the title page of United States Patent 2,980,090, showing the patent dates and inventors

There were at least seven important Bendix patents related to their original electronic fuel injection system, but this is the most important, covering many of the fundamentals. The first paragraph notes that this is a continuation-in-part of a previous application Bendix had filed a year earlier (in February 1956) and subsequently abandoned. (Illustration: Excerpt of U.S. Patent No. 2,980,090, “Fuel Injection System,” Robert Winfield Sutton, Stephen G. Woodward, and Curtis A. Hartman (assignors to The Bendix Corporation), filed 4 February 1957, patented 18 April 1961)

We found more substantive support for Ludvigsen’s summation in the Bendix fuel injection case study in Cases in Competitive Strategy, a 1983 book by Harvard business professor Michael E. Porter that draws on Bendix internal records and interviews with Bendix personnel; in Walter Kaiser’s 2004 history Bosch and the Automobile, 1950–2003: A Review, which addresses the matter from the Bosch perspective; and in later remarks by Hermann Scholl, who since 2012 has been the Bosch Group honorary chairman.

A central point of these accounts is that The Bendix Corporation was not keen to completely relinquish its control of electronic fuel injection technology. Contrary to what some sources have asserted (for example, Don Sherman in a 2021 Hagerty Media article on the history of fuel injection), Bendix did not simply sell all rights to the old Electrojector system or its related patents to Bosch. Instead, Bosch obtained a license to manufacture electronic fuel injection systems based on certain Bendix patents in exchange for per-system royalty payments. (This wasn’t the first such agreement between these two leading automotive suppliers; in the late 1920s, for example, Bosch had manufactured its own versions of Bendix electric starters under license from Bendix.) There was also a cross-licensing agreement, apparently contained in one or more subsequent contracts, that gave Bendix access to related Bosch patents and technological improvements. The deal imposed significant territorial restrictions on where each party could market or sell electronic fuel injection systems — the U.S. and Canada for Bendix; Germany and Brazil for Bosch — and required mutual approval for sales or licensing agreements outside those territories, such as the subsequent Bosch license deals with Japanese companies.

Curiously, published accounts are inconsistent as to the time frame of these agreements. Scholl suggests that the cross-licensing agreement was concluded around 1970, after Bendix blocked Bosch from entering into development deals with GM and Ford. Kaiser says the basic patent license was concluded in July 1968 and the reverse license deal that October, while Porter’s account indicates that Bosch approached Bendix in early 1967 about a patent license agreement and concluded the agreement in late 1967. We contacted Bosch for clarification, and while the actual contracts are confidential (and thus were not available to us for review), it appears the initial license agreement was completed in July 1966 (not 1968), the cross-licensing terms in October 1968; the agreements were subsequently amended a number of times.

Quantifying how much influence the Electrojector system had on the technical development of D-Jetronic is a more complex matter. Bosch engineers and officials definitely knew of the Bendix system: Bosch management board member Walter Lippart had first heard about it in 1954, when Bendix was first demonstrating its prototype to automakers, and the Bosch Corporate Archives still have a copy of the 1957 SAE paper on the Electrojector with handwritten marginal notes in German. Walter Kaiser suggests suggests that the initial Bosch ECGI work may have been a direct response to the Bendix development; the companies were after all competitors, and undoubtedly studied one another’s published technical works with some attention.

Color photo of individual Bosch D-Jetronic components laid out on a table (Robert Bosch GmbH, Corporate Archives, 1967 6 001 07018)

Components of a 1970 or later Bosch D-Jetronic system for air-cooled four-cylinder engines. Top row, left to right: auxiliary-air device, ignition distributor with pulse triggering points, manifold pressure sensor, fuel filter, fuel pump. Second row, left to right: throttle-valve switch, fuel pressure regulator, intake air temperature sensor, thermo-time switch, engine temperature sensor, cold-start valve. Bottom row, left to right: spark plugs, ECU, injectors. (Photo copyright Robert Bosch GmbH, Corporate Archives)

It’s not unlikely that Bosch would have studied ECGI regardless, but it seems reasonable to suppose that the knowledge that a major rival was close to mass production on its own electronic fuel injection system — and thus concern about being left behind on an important technological development — may have given the Bosch project an impetus and urgency it might not have otherwise had.

We were unable to determine whether there was any direct two-way consultation between Bosch and Bendix engineers during the initial development of the Bosch ECGI project. The agreement between Bendix and Bosch provided for technical assistance and, according to Porter’s account, permitted each party to visit the other’s facilities, but it appears that those contractual provisions were not added until October 1968, and the only specific indication we found of those provisions being exercised was a 1974 Bendix study of Bosch manufacturing methods related to electronic fuel injection. Our suspicion is that any direct technical dialogue that may have taken place was not until after the D-Jetronic system was already in production, although we must emphasize that this is still only a theory.

B&W photo of an early Bosch D-Jetronic electronic control unit being bench-tested (Robert Bosch GmbH, Corporate Archives, 1967 07786)

For the first two years of D-Jetronic production, the electronic control units were made for Bosch by Blaupunkt, but in 1969, Bosch brought ECU assembly in-house in the interests of tighter quality control. (Photo copyright Robert Bosch GmbH, Corporate Archives)

Electrojector vs. D-Jetronic

In any event, the D-Jetronic system was quite similar to the Electrojector in concept and operating principles. Because the Bosch system differed somewhat from application to application and evolved over the years, how closely it resembled the old Bendix system depended somewhat on which D-Jetronic iteration you were comparing, but the systems were sufficiently alike that it’s easier to summarize their salient differences:

  • Fuel pressure: D-Jetronic maintained a fuel pressure of about 28.5 psi (1.97 bar), roughly twice that of the production Electrojector systems, probably for better mixture formation.
  • Pressure sensor: Like the Electrojector, D-Jetronic used speed-density metering, but its pressure sensor used a movable armature attached to a pair of aneroid bellows in a chamber responsive to intake manifold vacuum, rather than a crank-arm potentiometer. The armature had no contacts to wear, and using the aneroids (whose internal air pressure was effectively zero) meant the sensor effectively measured manifold absolute pressure rather than simply manifold vacuum, eliminating the need for separate devices to compensate for barometric pressure.
  • Fuel cutoff: D-Jetronic cut off fuel to the injectors during deceleration and overrun, as the Electrojector did, but the cutoff was controlled electronically, based on the engine speed signal from the triggering selector in the distributor, rather than signaled through changes in manifold vacuum. Some later applications removed the cutoff circuitry, as it tended to produce spikes in hydrocarbon emissions when the fuel supply resumed.
  • Trigger contacts: Although D-Jetronic used mechanical points within the ignition distributor to trigger each pulse and then energize the injectors, it energized the injectors in groups rather than sequentially. This meant that injection wasn’t timed to coincide with valve opening or ignition timing, but Bosch, like Chrysler, had concluded that phased cyclic timing offered little benefit for port injection and made the triggering circuitry more complicated.

Early D-Jetronic systems shared a number of the same design flaws as the Electrojector, including poor cold start performance at very low temperatures (below -13°F/-25°C) and inadequate acceleration enrichment. D-Jetronic initially provided for momentary full load enrichment using a vacuum diaphragm switch, which was similar to the one on the Electrojector and had the same limitations. By the end of 1969, Bosch had instead incorporated this enrichment functionality into the pressure sensor itself, as illustrated below, and added an air temperature sensor to the intake manifold to compensate for increased air density at low temperatures so the mixture wouldn’t become too lean in cold weather.

B&W schematic of the D-Jetronic pressure sensor with full-load enrichment, with the major components labeled "Full-load stop," "Diaphragm," "Part load stop," "Aneroids," "Core," "Secondary winding," "Armature," "Primary winding," "Valve," "Damping," and "Leaf spring" (Robert Bosch GmbH, Nov. 1969 technical report Fig. 6)

Unlike the Electrojector, D-Jetronic used a contactless manifold pressure sensor, where increases in intake manifold pressure would compress the evacuated (aneroid) bellows and move the control cone of the spring-loaded armature into the core (leftward), increasing the impedance in the sensor circuit and thus the pulse duration. The section at the left, added in 1969, served to shift the support for the bellows farther to the left in response to a sudden increase in manifold pressure, further increasing impedance. It had the same purpose as the old pressure switch: providing momentary additional enrichment for smoother transient response. (Illustration copyright Robert Bosch GmbH, Corporate Archives)

At the same time, the throttle-valve switch was redesigned to incorporate an additional set of drag switch contacts, which provided a small amount of additional enrichment when the throttle valve changed position, for better transient response.

B&W schematic of the D-Jetronic throttle-valve switch, with the major components labeled a (idling contact), b (contact plate), c (lever), d (drag switch contacts), and e (contact plate) (Robert Bosch GmbH, Nov. 1969 technical report Fig. 7)

Originally, the D-Jetronic throttle-valve switch (like the one on the Electrojector) was used mostly for idle control. The revised switch in fall 1969 added drag switch contacts (d) that triggered additional enrichment in response to throttle motion, which was intended to avoid “flat spots” in engine response during abrupt changes in throttle position. (Illustration copyright Robert Bosch GmbH, Corporate Archives)

To address the previous cold start problems, D-Jetronic also added an auxiliary injector in the manifold, which Bosch called the cold-start valve, which sprayed finely atomized fuel into the intake manifold if the starter engaged below a certain temperature. The cold-start valve was controlled either by a thermoswitch, which closed the valve upon reaching a certain temperature, or a thermo-time switch, which automatically closed the valve after a certain period to avoid fouling the spark plugs.

Bendix Electronic Fuel Injection, Round 2

For the handful of engineers and managers within Bendix who were still believers in electronic fuel injection, the Bosch deal was at once validating and galling: Electronic injection now had a viable market niche, and was being offered by some prestigious European makes, but it had been a decade since Bendix had made or marketed a fuel injection system under its own name, and the term of the most important Bendix electronic fuel injection patents was already more than half over.

Bendix executives and engineers popped up regularly in the automotive press and in trade publications to assert that electronic fuel injection would soon see widespread industry adoption, particularly following the passage in late 1970 of the Muskie Act (Public Law 91-604), which called for much tougher auto emissions standards. Behind the scenes, however, Bendix remained very reluctant to make any significant investment in fuel injection, and was only willing to fund research and development work to the extent that royalty payments from Bosch covered the cost. John (Jack) Campbell, EFI Systems manager for Bendix, later lamented that he “spent more time selling inside the company than outside the company.”

B&W line drawing of the Chevrolet Cosworth Vega DOHC engine, cut away to illustrate the details of the cam drive, valve gear, and pistons (GM Media Archive X73100-0550 - cropped)

Conceived in 1970 and designed by engineers Cal Wade of Chevrolet and Mike Hall of Cosworth, the fuel-injected twin-cam, 16-valve Cosworth Vega engine was intended to become the basis of a Formula 2 racing engine, although porosity problems with the aluminum block did not allow the engine to develop enough power to be competitive. The racing version was abandoned in 1973, and the street version didn’t arrive until the spring of 1975, two years later than originally planned. (Illustration: General Motors LLC)

Campbell later claimed that by 1971, this reticence kiboshed his negotiations with Ford Motor Company regarding installing Bendix electronic fuel injection in the Lincoln Continental Mark Series. Ford was initially interested, but balked when Bendix Automotive Group senior management demanded that Ford agree to pay up to $4 million upfront to underwrite the development costs. As late as 1974, some industry observers still expected that Bendix electronic injection would show up next on a senior Ford model, but by then, Ford had long since turned its attention elsewhere.

We assume Bendix made similar demands of Chevrolet, which around the same time expressed interest in adopting electronic fuel injection for the Cosworth Vega, a planned high-performance version of the new Chevrolet Vega subcompact with a twin-cam, 16-valve aluminum head designed by England’s Cosworth Engineering. Chevrolet engine design engineer Calvin (Cal) Wade had already approached Rochester, which had made the defunct Ramjet mechanical injection system for Chevrolet and Pontiac, but they weren’t interested in electronic injection. Bendix was more amenable: Chevrolet wasn’t daunted by the cost, since Wade’s boss, general manager John DeLorean, saw the Cosworth project as a halo model and a proof of concept, and while DeLorean hoped to eventually offer fuel injection in the rest of the Vega line, the Cosworth Vega would be a low-production limited edition of perhaps 5,000 units, a modest commitment.

Press photo of engineer Cal Wade, in a gray suit, with a preproduction Cosworth Vega engine and transmission on a test stand (GM Media Archive C2325-0078)

Chevrolet engineer Cal Wade poses with a preproduction example of the Cosworth Vega engine he shepherded through a troubled development. The engine pictured isn’t the final production version, which had two separate throttle bodies instead of the single conjoined version fitted here. (Photo: General Motors LLC)

The first Cosworth Vega test engines were carbureted, but by April 1972, GM president Ed Cole was able to test-drive an injected prototype. DeLorean initially hoped to put the Cosworth Vega in production as a late 1973 model, but development was slow, and it wouldn’t be until early 1974 that Chevrolet actually began the time-consuming EPA certification process for the injected twin-cam engine.

In the meantime, Bendix entered negotiations with Cadillac, whose general manager, Robert D. Lund, invited Campbell to Cadillac headquarters to discuss offering electronic fuel injection system on a new compact model that would eventually become the first K-body Cadillac Seville. Since the new car was notionally intended as a Mercedes fighter, Lund had decided fuel injection was a must, for reasons of prestige as well as performance, and he was amenable to underwriting the upfront development costs. Unlike the Chevrolet deal, however, Cadillac envisioned a much more substantial production commitment: at least 300,000 systems over five years. This apparently unnerved Bendix president W. Michael Blumenthal, who insisted on going over the heads of both Campbell and Lund to negotiate the contract terms directly with Ed Cole. Nonetheless, by late 1973, GM and Bendix had a deal.

At this point, it belatedly became clear that for all the noise Bendix had been making in the press about the future of fuel injection, the company was painfully ill-prepared for actual series production of electronic injection systems. Bendix had no facilities to manufacture the solenoid-controlled injectors, no production experience with complex solid state electronics, and almost no engineers familiar with recent developments in microprocessors.

1976 Cadillac Seville engine compartment, a press photo of the fuel injected Oldsmobile 350 cubic inch V-8 (GM Media Archive C2506-R21-0003)

The 1976–1979 Cadillac Seville used a 350 cu. in. (5,737) cc Oldsmobile V-8, although Oldsmobile never offered the Bendix injection system. (Note the “ELECTRONIC FUEL INJECTION” lettering on the air cleaner.) The sole transmission was the three-speed TH375, a TH400 with a shorter tail shaft. Although the injected V-8 had decent power for the time, the hefty curb weight of the Seville and a standard 2.56:1 axle ratio sapped any performance pretensions. (Photo: General Motors LLC)

Given those issues, one might well ask why Cadillac, at least, didn’t simply go to Bosch. The answer is that the territorial restrictions in the cross-licensing agreement with Bendix appear to have prohibited Bosch from selling electronic fuel injection systems to American automakers, which left Bendix the only real game in town. Cadillac chief engineer Robert J. Templin said later that Cadillac selected Bendix because there were no contemporary alternatives “worth a damn.”

As we mentioned earlier, the agreements between Bendix and Bosch provided for mutual technical assistance. We don’t know to what extent Bendix availed itself of those provisions in the development of the Chevrolet and Cadillac fuel injection systems, but Porter’s case study says that Bendix manager Walter Schauer went to Germany for several months in 1974 to study Bosch manufacturing methods, and Bendix looked to Bosch to supply injectors and certain other components (such as throttle-valve sensors) for the GM injection systems. The latter point became yet another logistical headache: According to Porter, Bosch didn’t have enough existing production capacity to supply the almost half a million injectors a year Bendix needed to meet its Cadillac commitment, and wasn’t willing to add another injector plant without a longer-term commitment, which Bendix management was reluctant to make. The eventual compromise was for Bendix to split its injector orders between Bosch, Diesel Kiki, and Nippon Denso.

With the Cadillac delivery deadline looming just 18 months after the signature of the contract, Bendix scrambled to establish ECU production in a factory in Newport News alongside existing air pump assembly lines (not the optimum environment for delicate electronics) as Bendix engineers rushed through multiple last-minute redesigns of the ECU circuitry. The Chevrolet system also had to undergo further revisions: One of the prototype Cosworth Vega engines had failed its EPA durability testing with burned exhaust valves, and the production delays meant the engine had to be updated to meet the more stringent 1975 emissions standards, which cut the allowable hydrocarbon and carbon monoxide limits by more than half compared to 1974.

Cutaway illustration of a 1975–1976 Chevrolet Cosworth Vega engine, with the intake passage highlighted in blue, the combustion chamber and exhaust port highlighted in red, the water jacket highlighted in light green, and the catalytic converter and crankcase highlighted in orange (GM Media Archive X73100-1046)

The twin-cam Cosworth Vega engine displaced 122 cu. in. (1,995 cc) and made 110 hp (kW) and 107 lb-ft (145.4 N-m) of torque, much less than originally announced due to tougher regulatory requirements. While the fuel-injected four complied with both federal and California emissions standards for 1975–1976, concerns about emissions durability led to the inclusion of secondary air injection and a two-way catalytic converter. Chevrolet engineers said these imposed little power penalty, attributing the twin-cam four’s disappointing output to the restrictive muffler needed to comply with drive-by noise regulations, which reportedly cost 21 hp (15.7 kW). (Illustration: General Motors LLC)

All this chaos helps explain why the second-generation Bendix electronic injection system was something less than state-of-the-art even for 1975. While electronic injection still seemed novel and futuristic in concept, the Bendix system remained wholly analog and relied on air/fuel maps that were hardwired into the control modulator circuitry. After early service issues, Bendix added some “limp-home” fail-safe modes, but the ECU wasn’t programmable, so there were different iterations of the ECU for each application, adding to production costs. Speed-density metering based on manifold absolute pressure was also looking a little old-hat by 1974–1975. Bosch was already phasing out the D-Jetronic system in favor of the latest L-Jetronic (sequential electronic) and K-Jetronic (continuous mechanical) systems, both of which used mass airflow rather than manifold absolute pressure as their principal control variable. Although adding an airflow meter to the intake path cost some power, Bosch engineers believed that mass airflow metering avoided the acceleration enrichment issues that had been a persistent shortcoming of speed-density metering, provided better idle stability and transient response, was less affected by exhaust gas recirculation (EGR), and was more tolerant of variations in engine wear and tune. Speed-density metering never entirely went away (Toyota, for instance, used both speed-density (EFI-D) and mass airflow (EFI-L) systems on different home-market models throughout the eighties), but mass airflow systems remain vastly more common today, particularly since the introduction in the early eighties (on Bosch LH-Jetronic systems) of hot wire airflow sensors, which are less restrictive than earlier flap-type airflow meters.

Emissions durability was one of the Bendix system’s most significant shortcomings. Its metering was precise enough to let injected engines meet 1975 and 1976 federal and California emissions standards without a catalytic converter so long as the engine was operating at factory spec, but both federal and California emissions rules also required engines to maintain their exhaust emissions compliance for 50,000 miles (81,000 km) with only limited maintenance (the durability test the Cosworth Vega engine had failed in April 1974). The Bendix ECU couldn’t correct for combustion chamber carbon deposits, increased back pressure, vacuum leaks, or other common age- or tuning-related changes in volumetric efficiency, which could throw off the metering enough to eventually put the engine out of compliance. Both Cadillac and Chevrolet therefore opted to use catalytic converters with the injected engines, with the Seville engine also using exhaust gas recirculation. The Cosworth Vega didn’t have EGR, but added a novel air injection system Chevrolet called Pulse Air.

B&W press photo of a 1975 Chevrolet Cosworth Vega engine, showing the twin throttle bodies of the fuel injection system, the HEI distributor, and the hoses across the valve covers for the Pulse Air system (GM Media Archive X73600-0623)

The production-spec Cosworth Vega engine had dual throttle bodies, high-energy ignition, and a secondary air injection system called Pulse Air. The latter used exhaust pulses to draw intake air through one-way check valves (in the pipes extending over the valve covers) into the two-way catalytic converter, which promoted oxidization to reduce hydrocarbon and carbon monoxide emissions. Chevrolet claimed the system was as effective as an air injection pump, but consumed 6 hp (4.5 kW) less than a pump. (Photo: General Motors LLC)

The fuel injection system Bendix provided for Cadillac and Chevrolet was very similar to late D-Jetronic systems, differing mainly in minor details. For instance, since the GM injected engines used high-energy ignition, the distributor used reed switches rather than breaker points to transmit spike signals to the ECU. The GM systems also ran higher fuel rail pressures (nominally 39 psi/2.69 bar) and had dual electric fuel pumps, one on the chassis, and a second, called a boost pump, in the tank itself, to help prevent vapor lock. There were a few other peculiarities as well: The Cadillac system triggered its injectors in alternating groups of four rather than in pairs as on eight-cylinder D-Jetronic systems, while the Chevrolet system, which normally triggered the injectors in alternating pairs, would trigger all four injectors simultaneously at engine speeds over 6,000 rpm.

Illustration showing photos and drawings of the major components of the Cadillac electronic fuel injection system, superimposed on a drawing of a 1976 Cadillac Coupe De Ville: Throttle position switch; throttle body; fast idle valve (in throttle body); coolant temperature and air temperature sensors; electronic control unit; manifold air pressure [sensor]; fuel pump; fuel filter; injectors (8); fuel pressure regulator; fuel rail; and speed sensor (1976 Cadillac Shop Manual, Fig. 6-110)

The major components of the Cadillac and Chevrolet versions of the Bendix electronic fuel injection system were substantially the same, although of course the Cosworth Vega system had only four injectors rather than eight. Both versions had dual fuel pumps, one in the tank and one on the chassis. (Illustration: General Motors LLC)

Cadillac and Chevrolet Electronic Fuel Injection in Production

Chevrolet and Bendix had expected that the Cosworth Vega would be the first GM car with electronic fuel injection, which it was, but only barely: The injected Cosworth Vega bowed on April 17, 1975, as a late 1975 model, while the new Cadillac Seville arrived just five days later as an early 1976 model.

1976 Chevrolet Cosworth Vega front 3q, a black hatchback coupe with gold pinstripes (Aaron Severson)

The Cosworth Vega was never intended as a big-volume seller, but with its late arrival, disappointing performance, and hefty price tag ($5,916 for 1975, $6,065 for 1976), production didn’t even reach the 5,000 units originally anticipated, totaling 3,507 cars in 16 months. (author photo)

1976 Cadillac Seville front 3q, a press photo of a Brentwood Brown sedan with brown padded roof and whitewall tires (GM Media Archive C2506-0068)

The 1976 Cadillac Seville cost twice as much as a Cosworth Vega — list price started at $12,479, more than an Eldorado convertible — but its sharp styling and more rational exterior dimensions struck a chord with Cadillac customers, and it was a profitable seller, moving 60,127 units for the elongated 1976 model year. (Photo: General Motors LLC)

While the Bendix injection system was standard on both the Cosworth Vega and the Seville, it was also available as an expensive option on most other Cadillac models, presumably to ensure that Cadillac got full use out of the 60,000 systems a year Bob Lund and Ed Cole had committed to buy from Bendix. On other Cadillacs, the option initially listed for about $600, reflecting the system’s high cost: Bendix charged Cadillac more than $325 per system, at least four times the manufacturer cost of a conventional carburetor in that era; the ECU and injectors accounted for roughly 60 percent of the price. Bendix anticipated that the unit cost would come down as production ramped up and the company established its own injector factory, but it doesn’t appear things worked out that way. By 1979, the price tag of the system had risen to $783.

From a performance standpoint, the benefits of the Bendix system were incremental. Cadillac forewent resonance supercharging, opting to use basically the same intake manifolds for carbureted and injected engines, although the ones for injected engines had no manifold heat risers. On the big Cadillac 500 cu. in. (8,194 cc) V-8, fuel injection added 25 horsepower (18.6 kW) and 40 lb-ft (54.2 N-m) of torque, but the 350 cu. in. (5,737 cc) Oldsmobile engine in the Seville gained only 10 hp (7.5 kW) relative to its four-barrel Olds brethren, while the later 425 cu. in. (6,970 cc) Cadillac engine claimed a 15 hp (11.2 kW) edge over its carbureted counterpart. In principle, the injection system improved fuel economy, but even using that term in connection with any mid-seventies Cadillac seems slightly absurd.

1977 Cadillac Seville, front fender "Seville" and "Fuel Injection" badges on a Naples Yellow sedan (Aaron Severson)

Bendix electronic fuel injection was available on all Cadillac models for 1977, but it was standard only on the Seville, helping to justify that model’s higher list price (and mechanical commonalities with other, notionally lesser GM cars). (author photo)

Fuel injection did provide noticeably better driveability than contemporary carbureted engines, at least so long as the system was working properly, but the Bendix system could be very troublesome. A Popular Mechanics owners survey reported numerous problems with the electronic control unit, perhaps reflecting the chaos of early ECU production. Bendix said the reliability goal was a first-year warranty return rate of 1.5 percent, but even before the system went on sale, Bendix engineers publicly admitted it would take some time to reach that target. Owner perception of the system’s reliability may also have been skewed by the Cadillac and Chevrolet service policy of replacing the ECU rather than attempting to repair it, which resulted in some cars having their ECUs replaced more than once.

1977 Cadillac Seville front 3q, a Naples Yellow sedan with yellow padded roof and wire wheel covers (Aaron Severson)

A more vertical grille was the only noticeable change for the 1977 Cadillac Seville (unless you spotted a rare example without the padded roof), but it got four-wheel discs, some minor chassis changes, even more standard equipment, and an $880 price hike. Sales totaled 45,060 — still enough to be very profitable, but short of the original 60,000-unit target. (author photo)

Until near the end of its life, the second-generation Bendix electronic fuel injection system lacked what would prove to be the real “killer app” in fuel delivery technology: “closed-loop” operation, using lambda sensor feedback (see the sidebar below) to keep the mixture as close to stoichiometric as possible. Bendix was certainly aware of the development of closed-loop feedback systems, which Bosch had been pursuing since early in the decade. In fact, Bendix engineers John Camp and Todd Rachel presented a paper on that subject at the SAE Automotive Engineering Congress & Exposition in February 1975, two months before the debut of the Seville. However, Bendix didn’t add oxygen sensor feedback to its electronic fuel injection system until 1979 — two years after the Volvo introduced the Bosch-developed Lambda Sond system — and only on the California-bound 1979 Seville and 1980 Eldorado, which had a new closed-loop control system designed by Pontiac, combined with what GM called its “Phase II” three-way catalytic converter. (The Cosworth Vega was long gone by then, having been dropped in July 1976.)

After that, Cadillac abandoned the Bendix system in favor of a more modern digital engine management system, developed by the GM corporate Engineering Staff, which combined mixture control with digital management of spark timing, exhaust gas recirculation, idle speed, and other emissions-related functions. This system was offered in both carbureted and injected versions. The injected version used a new in-house throttle-body injection (TBI) system, still with speed-density metering, but now with only one injector per cylinder bank. This was a compromise, but it was significantly cheaper than port injection, and the system’s digital controls were far more sophisticated than the analog ECU of the Bendix port injection system. (Bendix subsequently developed its own digitally managed single-point injection system, which debuted on the 1983 Renault Alliance.)

EFI Aftermath

Although it wasn’t nearly as hopeless as its Electrojector ancestor (or the misbegotten Oldsmobile diesel engine Cadillac also offered on the Seville from 1978 on), the second-generation Bendix electronic fuel injection system still has a checkered reputation, and it appears to have been a source of considerable frustration for all concerned. From Hermann Scholl’s perspective, Bendix had insisted on shutting Bosch out of the U.S. market only to develop an inferior system that was still overreliant on Bosch to supply crucial components. Jack Campbell and other Bendix executives interviewed for Michael Porter’s case study were annoyed at their leadership’s ongoing ambivalence about making actual use of a technology the company had pioneered. Both sides would probably concur that the fundamental problem was Bendix management’s reluctance to make any substantial investment in fuel injection, which in retrospect seems positively self-sabotaging.

As for Cadillac and Chevrolet, it seems the Bendix system mostly served to reinforce existing Detroit prejudices about fuel injection. Although Robert Lund considered it a marketing necessity for the Seville, the system was hugely expensive, offered only very modest performance benefits, and brought additional service headaches. On top of that, it ultimately wasn’t even that helpful for emissions compliance, particularly once it became possible to adapt carburetors or throttle-body injection for closed-loop operation, which was significantly less expensive.

Press photo of a Cadillac Electronic Fuel Injected 5.7 Litre V-8 with High Energy Ignition (HEI) in a display case marked with the Seville logo (GM Media Archive X73100-0550 - cropped)

The fuel-injected 350 cu. in. (5,737 cc) Oldsmobile V-8 became a museum piece after 1980. For its final year, it was offered only on the California-spec Cadillac Eldorado, with closed-loop feedback control and 160 hp (119.3 kW). (Photo: General Motors LLC)

Bosch faced similar issues in Europe, where it struggled throughout the seventies to sell its L-Jetronic electronic injection system to automakers who regarded the mechanical K-Jetronic as a cheaper and safer bet. Many existing Bosch customers soon abandoned the earlier ECGI systems for K-Jetronic. L-Jetronic was more successful in Japan, which adopted U.S.-style emissions standards beginning in the mid-seventies — in 1973, Bosch formed a joint venture with Diesel Kiki, Nissan, and Isuzu to market locally built L-Jetronic systems in Japan, and Bosch subsequently licensed Nippon Denso to manufacture L-Jetronic for Toyota (as EFI-L) — but it wasn’t until European emissions rules began to tighten in the late eighties that K-Jetronic fell behind. K-Jetronic and the hybrid KE-Jetronic system, with additional electromechanical analog controls, both survived into the nineties, but by the end, they had actually become more expensive to build than the far more sophisticated Bosch digital engine control systems — belatedly fulfilling the prediction Winkler and Sutton had made more than 35 years earlier.

Today, of course, carburetors and mechanical fuel injection are long obsolete for passenger cars and light truck applications, while electronic fuel injection is ubiquitous. Were the Electrojector and D-Jetronic the progenitors of modern fuel injection? Sort of, if you squint a bit, but in the same way the electric typewriter was the predecessor of the modern word processing app. The success of electronic fuel injection hinged on subsequent advances in microprocessors and sensor technology that hadn’t been envisioned when either system was designed. With their analog ECUs and mechanical sensors, the Bendix and Bosch D-Jetronic systems would have been only incrementally more capable than carburetors of surviving the regulatory pressures of the eighties and beyond (and without those regulations, it would certainly have been at least another decade or two before electronic fuel injection saw any widespread use).

Left front fender badge reading "V8-6-4 FUEL INJECTION" on a Sandstone 1981 Cadillac Seville (Greg Gjerdingen)

This badge indicates that in addition to fuel injection (the new throttle-body system with two injectors), the digital engine management system of the 368 cu. in. (6,033 cc) V-8 in this 1981 Cadillac Seville incorporates another conceptually sound feature introduced before it was really ready for public airing: “modulated displacement” (more commonly known as cylinder deactivation), using a system developed by the Eaton Corporation. Reliability problems led Cadillac to drop this feature after a year, and many unhappy owners eventually disconnected it. (Photo: “1981 Cadillac Seville (14301994740)” by Greg Gjerdingen, which is licensed under a Creative Commons Attribution 2.0 Generic (CC BY 2.0) license)

If there’s any moral to this story, it’s that there’s no singular arc of progress in automotive engineering. We’re used to thinking of technology evolving in clear-cut ways from primitive mechanical systems to advanced modern electronics, but the reality is often more complicated. Electronic fuel injection preceded many fairly successful mechanical injection systems; some automakers who’d previously used multipoint electronic injection later exchanged them for mechanical or throttle-body systems; and carburetors persisted on cheaper and lower-volume models well into the nineties. It’s been more than 40 years since there was any serious doubt about the advantages of electronic fuel injection, which today makes possible a combination of power, fuel economy, driveability, and emissions performance many automotive engineers of the seventies would have insisted was impossible, but it took years of cost reductions, production improvements, and increasingly stringent regulatory demands to finally make it universal.



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(Toyota City, Japan: Toyota Motor Corporation, November 1984); “Two Mercedes Surprises,” The Autocar 12 February 1954: 209–210; U.S. Department of Health, Education, and Welfare, “Control of Air Pollution from New Motor Vehicles and New Motor Vehicle Engines” [establishing rules and regulations for Part 85 of Title 45], Federal Register Vol. 31, No. 61 (March 30, 1966), Part II: 5170–5178; Maarten Van Eijck, The Heckflosse Homepage, www.heckflosse.nl, last accessed 22 February 2024; Paul Van Valkenburgh, “The Eleven Year Car,” Sports Car Graphic February 1970, reprinted in Volvo 1800 Ultimate Portfolio, R.M. Clarke, ed. (Cobham, England: Brooklands Books Ltd., ca. 2006): 128–131; VinceC, “Automotive History: 1975–1979 Cadillac Electronic Fuel Injection — GM’s (Gladly) Forgotten Fuelie — A GM Deadly Sin?” Curbside Classic, 30 July 2021, www.curbsideclassic. com/ automotive-histories/ automotive-history-1975-1979-cadillac-electronic-fuel-injection-gms-forgotten-fuelie/, last accessed 22 January 2024; Ron Wakefield, “Technical Analysis: Cadillac Seville: America’s new Mercedes-size luxury car,” Road & Track Vol. 26, No. 10 (June 1975): 47–50, and “Engineering the Modern Automobile: Fuel Injection: An examination of the fuel injection systems now in production,” Road & Track Vol. 19, No. 11 (July 1968): 59–64; Brooks Walker and Harry E. Kennedy, U.S. Patent No. 2,018,159, “Electrical Fuel Injection System for Internal Combustion Engines,” filed 20 June 1934, patented 22 October 1935; Harry Walton, “How Good Is Fuel Injection?” Popular Science Vol. 170, No. 3 (March 1957): 88–93; Gary Witzenburg, “Driving the 1980 General Motors model,” Popular Mechanics Vol. 152, No. 4 (October 1979): 97–99, 236–241; Tom Yates, “How GM’s throttle body fuel-injection system works,” Popular Mechanics Vol. 155, No. 2 (February 1982): 66, 68; Anthony Young, Chevy Classics 1955 • 1956 • 1957 (New York: Barnes and Noble Books, Inc., 1999); and Richard Zechnall, Günther Baumann, and Hermann Eisele, Robert Bosch GmbH, “Closed-Loop Exhaust Emission Control with Electronic Fuel Injection,” SAE Technical Paper 730566 (Warrendale, Pa.: Society of Automotive Engineers, 1973).

Remarks of former Bosch engineer Dr.-Ing. Hermann Scholl came from a transcript of his speech “40 Jahre elektronische Benzineinspritzung,” originally delivered 11 September 2007 in Frankfurt, Germany, and provided to us by Robert Bosch GmbH Corporate Archives (RB 3 0005 764).

Additional technical information on the Bendix Electrojector system came from Albert H. Winkler and Robert W. Sutton, “Electrojector — Bendix Electronic Fuel Injection System,” SAE Technical Paper 570060 (January 1957), SAE Transactions Vol. 65 (1957): 758–768; Bendix Products Division, Service Sales Department, Bendix Aviation Corporation, Bendix Electrojector [service manual, Form 10-1029] (South Bend, Ind.: Bendix Products Division of Bendix Aviation Corporation, August 1957); Chrysler Corporation Training Center, Fuel Injection [service training manual] (Warren, Mich.: Service Development & Training Department, Chrysler Corporation: August 1957); the following Bendix patents: Noble Franklin Pribble, assignor to Bendix Aviation Corporation, U.S. Patent No. 2,815,009, “Fuel Injection Control System,” filed 19 September 1956, patented 3 December 1957; Robert W. Sutton, assignor to Bendix Aviation Corporation, U.S. Patent No. 2,900,967, “Fuel Supply System,” filed 11 March 1957, patented 25 August 1959; Robert W. Sutton, Stephen G. Woodward, and Curtis A. Hartman, assignors to The Bendix Corporation, U.S. Patent No. 2,980,090, “Fuel Injection System,” filed 4 February 1957, patented 18 April 1961; Stephen G. Woodward, assignor to The Bendix Corporation, U.S. Patent No. 3,159,151A, “Fuel Supply System,” filed 24 August 1962, patented 1 December 1964; Stephen G. Woodward and Curtis A. Hartman, assignors to The Bendix Corporation, U.S. Patent No. 2,948,272, “Fuel Supply System,” filed 16 November 1956, patented 9 August 1960, and U.S. Patent No. 3,106,196, “Fuel Supply System,” filed 16 November 1956, patented 8 October 1963; and Albert H. Winkler, assignor to Bendix Aviation Corporation, U.S. Patent No. 2,884,916, “Fuel Supply System,” filed 13 December 1957, patented 5 May 1959, and U.S. Patent No. 2,888,000, “Fuel Supply System,” filed 27 February 1957, patented 26 May 1959; and Chrysler Corporation, Engineering Division, Technical Report No. 4406.530, 30 May 1959; Technical Report 4511.28, 1 October 1959; Technical Report 4511.33, 1 June 1960; Technical Report 4809.10, 7 May 1962; and Technical Report 4809.11, May 1962 (obtained via the Chrysler 300 Club website).



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  1. Great article

  2. I’ve heard that at least at first, Bosch sold Volkswagen the D-Jetronic system at cost because they wanted to get field experience with it. Do you know if that’s true?

    1. I haven’t read anything regarding how much Bosch charged Volkswagen for the early D-Jetronic systems, and I don’t claim to have any idea how their contracts were structured (which I suspect both Bosch and Volkswagen would be reluctant to divulge). However, I’m skeptical because that assertion is hard to reconcile with the scale of Volkswagen’s production commitment. Volkswagen saw themselves as up against the wall in a regulatory sense, so they didn’t dabble. Their initial orders were for 10,000 systems per month, with what I have to assume were pretty ironclad delivery deadlines! This wasn’t a matter of buying a few early ECGI systems to offer optionally in high-end models for familiarization purposes; Volkswagen was making D-Jetronic standard equipment on all U.S. Type 3 models as means of regulatory compliance (without which those models would have to be withdrawn from VW’s biggest export market). Also, given the magnitude of the investments Bosch had to make in development and manufacturing capacity, plus the Bendix royalty situation, even determining what “at cost” might mean under the circumstances would seem to be a complicated and subjective question.

      The only specific figure I have for the cost of the system was what Volkswagen charged for D-Jetronic as an option on the German 1600 TL, which was initially 600 marks. This was at a time when the exchange rate of the Deutschmark to the dollar was still fixed at 4:1, so that’s the equivalent of $150 USD, which does admittedly seem very cheap even for the time.

    2. I was thinking about this, and it occurred to me that this might be conflating the production D-Jetronic systems with the 40 preproduction prototype systems Bosch built in the autumn of 1965. Bosch retained some of those for testing and provided some to Volkswagen for evaluation and familiarization. I can readily believe that Bosch may have sold those systems to Volkswagen for a nominal cost, which is a different matter than the regular production orders that began two years later.

  3. Ridiculously comprehensive, as usual!

  4. Anecdotally, I worked on T3s in the mid-70s for about five years at an independent shop and a couple of dealers. D-Jetronic was extremely reliable except for leaky injector lines, the ~3 inch fabric covered rubber lines that are part of the injector. We’d simply cut off the integral swage and put on a new line using a small hose clamp.

    The most reliable component was the analog computer. As I recall there wasn’t a single electrolytic capacitor used. Rather, much more reliable tantalum capacitors were used which were much more suitable for automotive use, more resistant to temp swings and vibration. I probably worked on a couple thousand T3s and don’t remember replacing a single computer. I did replace a few fuel pumps and manifold pressure sensors.

    That was a long time ago so I might not remember exactly; I do remember customers praising their T3’s gas mileage compared to their carbureted T1s.

    1. According to Hermann Scholl’s remarks, the most persistent issue Bosch faced with the ECU was its wiring harness and connectors rather than its individual components, although the large number of the latter was a headache from a manufacturing quality control standpoint, and drove up the price. Other comments I’ve heard suggest that the aneroid bellows were the weak point of the MAP sensor — over time, the rubber of the bellows would crack, and the resulting air leaks would cause the sensor to malfunction, since it was set up with the assumption that the pressure inside the aneroids was effectively zero.

      1. I thought the T3 MPS sensor was a bit more sophisticated than a modern-day MAP sensor in that modern FI systems have downstream sensors – 02 sensors in particular – that provide additional info to the ECU. Maybe I’m wrong.

        As far as reliability, I wrenched T3’s in the humid Midwest. Perhaps the bellows were prone to crack in drier environments. And of course that wrenching was done 50 years ago. Ten years after that it’s likely a higher proportion of those diaphrams developed leaks.

        1. There’s a lot of detailed technical and troubleshooting information on D-Jetronic in Paul B. Anders’ 914 pages at https://members.rennlist.com/pbanders/ — Anders is an electrical engineer (which I am not!) who has also spent a lot of time wrenching on 914 systems (which I have not). He mentions that the MPS aneroids would eventually crack with a lot of full-load operation (see https://members.rennlist.com/pbanders/manifold_pressure_sensor.htm). It does seem reasonable to surmise that this might be exacerbated by aggressive driving styles and hotter/drier conditions, although Anders sees it as a design flaw, which also seems fair.

          The D-Jetronic MPS was unquestionably more sophisticated than the MPS in the Bendix Electrojector system, which wasn’t contactless, responded only to differential (not absolute) manifold pressure, and had a tendency to move to the extremes of its travel (something the Bendix patents note) rather than providing a really progressive response. However, the D-Jetronic sensor was still analog, it was mechanically complicated compared to a modern capacitive or varistor MAP sensor, it didn’t have its own temperature sensors (requiring separate correction for intake temp), and it didn’t have any kind of self-diagnosis capability. So, it was a step forward, but it definitely wasn’t the last word even for speed-density metering systems.

          It’s definitely true that the MPS was substantially more critical for D-Jetronic than the MAP sensors in later digital systems. D-Jetronic (and early L-Jetronic systems) had hardwired air-fuel maps, and they didn’t have memory in the way modern engine computers do. With digital controls, you can potentially store several sets of air-fuel maps as lookup tables and use those along with other sensor input data (coolant temperature, throttle position, lambda information from the O2 sensor) as a supplement or fail-safe in the event of sensor malfunction; the computer can also self-adjust for variations in volumetric efficiency due to age or state of tune. D-Jetronic couldn’t do any of that, and so it was heavily dependent on the proper function of the MPS, and on the engine’s volumetric efficiency remaining pretty close to the expected values.

  5. Thank you for this (well researched, as always) article. It answers a question that has puzzled me since the 1970’s- why didn’t Detroit go immediately to EFI in the 1970’s? The malaise era Detroit Carburetored engines were a such disaster and fuel injection was such an obvious answer. The answer as to why not, it seems, is Bendix. As the (then) owner of a mechanically fuel injected 1974 Alfa Romeo, I knew that fuel injection was the answer to fuel economy, drivability, and emission concerns, and I also knew that mechanical fuel injection was already obsolete. EFI was obviously the answer but “no one” adopted it.

    I had always thought that it was merely the big 3’s stinginess that kept them wed to carbs. VW had shown that EFI could be used economically and ‘reliably’ on inexpensive cars. However I didn’t know of Bendix’ stranglehold on the U.S. market. So while I was correct that it was old cigar-smoking pennywise, pound-foolish bean-counting fools, I misplaced them – they were at Bendix.

    1. I also came away feeling like Bendix really flubbed the whole thing: They pushed this technology to production before it was ready, alienated at least two major U.S. automakers in the process, and were then apparently prepared to just sit on their jealously guarded patents until the clock ran out. Even when they had a new customer waving money at them, they remained so reticent about making any big investment that it kept their costs and prices prohibitively high.

      That said, it isn’t the whole story. As Michael Porter notes, U.S. manufacturers had significant sunk costs in carburetor development and manufacture, and so from a capital investment standpoint, it was cheaper for them to keep modifying carburetor designs for emissions compliance than to switch to even single-point injection. Volkswagen was an unusual case because they decided their backs were to the wall AND they were prepared to eat more of the cost than most U.S. manufacturers would have deemed acceptable in order to maintain their price point. This is something that became a growing issue for Volkswagen during the waning days of the air-cooled era, as Bernhard Rieger discusses in his 2013 book The People’s Car: VW recognized that they needed to make improvements, but they also had to hold the line on price, so their profit margins began to shrink precipitously.

      The situation in Japan was perhaps more broadly representative. By the mid-seventies, Japanese automakers were also facing significant challenges in emissions compliance (their domestic standards were tougher than ours by 1978), so they were very interested in electronic fuel injection, but they weren’t prepared to swallow the significant price premium (especially since local manufacture was still royalty-encumbered). As a result, JDM adoption followed a pattern similar to what eventually happened here: Senior grades got fuel injection first, and it gradually spread downward, not becoming universal until much later. Some lower-grade models still had feedback carburetors well into the nineties. Their domestic trend was a couple of years ahead of ours, for a number of reasons, but the trajectory was roughly the same.

      The other oddity here is that Bosch was extremely successful for years with K-Jetronic, which arrived about five years after D-Jetronic and came very close to killing the Bosch electronic systems. K-Jetronic was a clever piece of work, much less complex than the older Bosch mechanical systems or the SPICA system in your Alfa and yet precise enough for emissions compliance, particularly with feedback control. Many European manufacturers traded D-Jetronic for K-Jetronic, even Mercedes and Porsche, and stuck with it for a surprisingly long time. Mercedes stuck with the electromechanical KE-Jetronic system through the early years of the R129 SL-Class, on which cost was presumably not a big issue. (I think the reason they finally switched to LH-Jetronic was that Bosch was phasing out the electromechanical systems, although OBD-II requirements would have forced the issue eventually anyway.)

    2. The other consideration is that many of the factors that have made modern electronic fuel injection so useful depended on the availability of relatively cheap, reliable digital processors. The earlier analog systems, even with closed-loop feedback control, didn’t have a memory, were only programmable by making physical changes to the control circuitry, and had little to no self-adjustment capability. Sixties digital electronics were not yet up to the task (the early Autonetics VERDAN computer used by the USN had a mean time between failure of only 15 minutes!), and while the technology evolved very quickly in the late seventies, I can’t really seeing it being successfully implemented in series automobile production much earlier than it actually was (which started around 1979–1980).

  6. Thank you, Aaron, for this discussion of the Bendix Electrojector system and its influences. My interest stems from back when I owned a Chrysler C300 many years ago, and as a member of the Chrysler 300 Club, read about this system. I always wondered about it, especially since its influence has become so widespread in the automotive world. I wondered, ‘What went wrong with the Electrojector?’

    As you describe it, the first implementations by Bendix were crude. But, the carburetor is a crude device, too, and the Rochester mechanical system was not so far removed from a carburetor, using venturi vacuum signals and metering rods. It was crude, too. But both the Bendix and the Rochester systems offered the ability to improve on air/fuel distribution, and there’s not much reason why the Bendix couldn’t have been successful in performing this task, if not successful in the market, like the Rochester was, more or less.

    As a general observation, I think that Detroit’s developmental weaknesses are highlighted by your description. This is especially due to the dismal performance of so many electronic aspects, such as the first HEI modules. Not much learning took place there, as I had an early Ford Taurus that was overall a good car, except for the TFI ignition module, which consistently failed.

    Bosch and Volkswagen seem to have tried a little harder, and stuck with the problem a little more. I would guess that Volkswagen customers in the late 60s and early 70s might have had a stronger affinity for the marque, as well. I recall that it was common to replace the Bosch system with carburetors back in those days.

    The Japanese seemed to do a better job at this, which was reflected in the marketplace. (The Acura/Sterling comparison is an interesting aside to this: taking a very reliable engine and making a disaster of it also demonstrates how car makers can be tripped up by electronics.)

    Even in my old Volvo/ Bosch S60, there are glitches in the computer operation that should have been worked out, but were passed on to the consumer, even though my car does work fine as long as I observe the limitations.

    I also found your mention of the aftermarket Conelec system interesting. I recall seeing Conelec fuel pumps available on the aftermarket decades ago, and wondered why this odd name popped up to compete against traditional brand products. Now, thanks to your thorough research, I know!

    Great article, thank you

    1. The conceptual challenge presented by moving from carburetion to electronic fuel injection is akin to the difference between learning to walk and trying to create a mathematical model to make a robot walk. This was particularly troublesome with starting (and especially cold start), which I sort of skimmed over, but was a big development hassle: You know you need a richer mixture for starting, especially when cold, but exactly how much for how long? And what do you do if the extra enrichment is fouling the plugs? It was a matter of trying to precisely define factors that previously got by with workable approximation, without the benefit of sensory feedback to allow self-correction or the ability to remember what did and didn’t work last time.

      Where the Electrojector really fell down was in the difference between theoretical models of electrical circuits and the more complicated physical realities. In theory, the injector valve operation was quite simple (energize the solenoid to open the valve, hold it for the requisite duration, and then cut the current and let the spring push the valve closed), but that didn’t take into account things like eddy currents generating enough of a residual magnetic field to keep the solenoid partially energized for too long. Even Bosch, which had extensive experience with mechanical injection valves for diesel engines, struggled with that at first, although they got it sorted more quickly than Bendix had.

      I don’t know that I’d call the Rochester Ramjet system crude; it’s not as intricate as the Bosch jerk-pump mechanical systems, but it’s a clever approach to mass airflow metering. It seems to have been designed as something that could eventually be mass pass produced relatively cheaply, although it would likely always have been more costly than a carburetor, and low volume kept it expensive.

      There’s no question that automotive electronics have had a rough learning curve. The environmental conditions are difficult (heat-cycling, vibration, dirt), and since the adoption of the technology has often been driven primarily by regulatory compliance, certain performance metrics have to be prioritized over all others. For obvious reasons, this has tended to be a bigger problem during periods where the regulatory requirements (usually emissions-related) are a moving target. A lot of what’s made such a difference in recent decades is integrated digital electronics with greater fault tolerance — both of faults with the electronics themselves and of mechanical variance — and the ability to learn and self-adjust. To return to my original analogy, the reason toddlers are able to learn to walk is not that they become mathematical geniuses, but that they’re able to adjust based on feedback and experience; they may still wobble and sway, but as they learn to compensate, they fall down less and less.

      1. Your pointing out the difference between learning to walk vs programming a robot to walk is well-taken, especially without feedback systems. The cold start issue, I also see now and take into acount.

        I would have done better to ponder the intricacies of injectors regarding magnetic properties that evidently tripped up early development efforts.

        When I used the word “crude” regarding the Rochester injection, I perhaps could have chosen my words better. I was thinking in terms of carburetion — which in one sense are simple analog mixing devices with provision for acceleration and cold start (and maybe a few others, depending on the implementation) — but in another sense do have complexity in those simple concepts which, when refined, can make for a pretty capable system. The Rochester uses the same analog systems and signal concepts, but rather than, say booster venturis and emulsion tubes, uses a straightforward constant injection into the port.

        Comparing this with later port injection systems with lots of signal inputs and a fairly complex computer program (which also incorporates spark control, an additional advantage), my comparison was in the vein of so many electronically controlled devices of today compared to manually of mechanically controlled analog devices from the 50s and before.

        You are right about the price of the Rochester system. As I recall from the 60s, many took it off for carburetors, while my neighbor would buy the systems for small sums and run them on his Chevys with performance and economy simultaneously. He claimed that it was only a matter of following the service manual correctly to achieve this — no surprise there!

        re: electronics, HEI only replaced points in its early ~1975 iteration. I recall it being of questionable reliability, such that one might want to keep an extra module in the glove box. However, by 1977, my vehicle with HEI was trouble free. I don’t see the technology changing sufficiently in those two years to justify a “learning curve” if adequate testing was done.

        Certainly not over 10 years later, with my Taurus’s thin film module, which was a failure looking for a place to happen, which it did on a number of unfortunate occasions.

        1. In a 1957 article I looked at, Roger Huntington reported the surly comments of some unnamed Detroit engineers to the effect that all early injection systems were essentially continuous because getting the injector valves in intermittent systems to close completely and on schedule was wishful thinking — not so much on and off as “flow” vs. “dribble.” That was essentially Chrysler’s experience with the Electrojector injectors, so they had a point, particularly given the short duration of timed injection pulses. (Pulse width for the Electrojector in normal driving was supposed to be between 1.0 and 4.5 ms, so you can see how a solenoid injector valve that took 8 or 9 ms to close fully would be a problem!) Also, Chrysler found, as Bosch later determined as well, that it really didn’t matter whether the valves were closed at the time of the pulse, which is why D-Jetronic and the seventies Bendix system triggered their injectors in pairs or groups rather than one at a time. For direct injection, it was useful to time the injection pulse to arrive after the intake valve had closed, so as not to spray fuel back into the port, but with port injection, it turned out not to make a meaningful difference. So, in that respect, timed intermittent injection did not have a particular advantage over continuous injection in sophistication or performance, which is also part of why K-Jetronic remained competitive for as long as it did.

          A key point that’s easy to misunderstand is that fuel injection for passenger car applications has always been computerized, whether it’s mechanical or electronic. A mechanical system is analog, of course, but so is D-Jetronic, and the fact that its computations were based on voltage and resistance doesn’t actually make them more computerized. This becomes especially apparent if you look at the workings of the early Bosch mechanical systems, which had a complex assortment of different mechanical sensors. They did the same things as the analog electronic sensors in the Electrojector, just not quite in the same ways. The advantage of the electronic system was ultimately in growth potential: It could be more readily adapted to incorporate digital memory and additional input parameters, although none of that was present in the early systems.

          The seventies were a time of very rapid development in electronic components, so there were sometimes significant differences in the span of two or three years. I haven’t studied HEI systems in any detail (there was an in-depth three-part article on Curbside Classic a couple years ago that covers the subject well), but early systems were dubiously reliable in ways that were worked out in relatively short order.

          The challenge of “adequate testing” during periods like the seventies and early eighties is that automakers were on a tight development schedule for regulatory compliance, which was a moving target. For instance, between 1975 and 1977, federal standards for oxides of nitrogen were lowered from 3.1 g/mi to 2.0 g/mi, while California NOx standards went from 2.0 to 1.5 g/mi and HC fell from 0.9 to 0.41 g/mi. Powertrain engineers were rushing to certify powertrains that met one set of standards while also scrambling to revise the hardware to meet the next set of standards, which meant there were a lot of essentially interim features that worked well enough for shorter-term needs, but weren’t going to be continued for long. This is the conundrum of regulation-driven change: It resulted in many headaches, but without it, a lot of the ultimately beneficial improvements in engine technology would never have become universal; cheaper cars would probably still be carbureted and have breaker-point ignition. I don’t think automakers necessarily handled these challenges well, but it would be a mistake to overlook how much of a challenge it frequently was.

  7. Excellent and fascinating article. I enjoyed the article so much I sent you $. Haha. The thing I find amazing is Bendix or Chrysler didn’t consider just running two larger injectors (instead of the 8 port injectors) at the throttle body. This would have slowed down the injector pulse width dramatically. Likely to a speed the fairly primitive control unit could have handled. As you seem to suggest they got pretty close then maddeningly just basically gave up

    1. Bendix did definitely consider throttle-body injection — in fact, the first illustration in their most important electronic fuel injection patent is of a throttle-body injection iteration of their concept. Throttle-body injection was discussed and proposed throughout the fifties, but nobody put it into production because the cost-to-benefit ratio just wasn’t worth it. Once you put mixture formation back into the throttle body, you lose most of the actual performance benefits of fuel injection: The manifold isn’t dry, it still needs to be heated (except for pure racing applications), and mixture distribution isn’t much better than with a carburetor. Single-point injection (i.e., one injector per bank) provides better fuel vaporization and more precise metering, which is better for emissions than carburetion, but that wasn’t very high on the agenda in the late fifties, and it was not enough to justify what still would have been a $200+ price premium. It would also have had much poorer performance than contemporary mechanical injection systems.

      The problem with the Electrojector was not that the control unit couldn’t handle the speed required for the pulse width range involved (although there were early problems getting enough amplification), it was that Bendix and Chrysler had very great difficulty getting the solenoid injector valves to close fast enough and completely enough to make the calculated pulse width values meaningful. Chrysler eventually got the closing time down to 0.8 ms, which was an order of magnitude improvement over the valves they initially got from Bendix, but the production tolerances were still so poor that they had to basically just hand-select matched sets of injectors. Having fewer injectors would not have helped that, but it would have meant that there wasn’t even a nominal performance benefit to the injection system.

      The Electrojector had some design limitations, but its principal failing was that getting the relatively straightforward concept to work reliably ended up being a lot more difficult than anticipated. Even Bosch, which had lots of experience with diesel injection valves, struggled with it, although the pressure of their sizable production commitments gave them strong incentive to work it out.

  8. My father bought my mother a 1 year old ’76 Seville in ’77. They loved the looks and didn’t want to hear my brother’s and my criticism of it’s ox-cart suspension and Nova roots.
    In any case, expecially for the era, the advantages of the EFI were immediately apparent. The engine started immediately with no need to “set” a choke, it never stumbled or hesitated, and considering the weight of the car, it got pretty good gas mileage and was reasonably fast. I recall burying the 85MPH speedometer so the pointer completely disappeared inside the dash and then set the cruise control.
    It did need to be towed a couple (several?) times due to not starting. It seems to me that I heard it was the HEI, not EFI that kept failing. I can tell you this though, my parents were not impressed when one of those tows was when I was using the Seville, when home from college on break, and it wouldn’t start in front of a liquor store about 1 AM on a Saturday morning….THAT I clearly remember.

    1. And I completely forgot to compliment on a wonderfully written and very informative story. I had wondered for a long time why AMC and Chrysler ended (or aborted in AMC’s case) their Electrojet option, and then, why it never reappeared.
      BTW, Bendix had a manufacturing facility in Towson, MD, which I believe made radar and radio systems. By coincidence, I work next to the old plant. In any case, I heard stories about 20 years ago, that they made the original EFI systems at that plant – I’d say that was nothing more than a story.
      Fantastic article!

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