Electrojector and D-Jetronic: Early Electronic Fuel Injection

Summary

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)

IMPORTANT AUTHOR’S NOTE

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 delivered. 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.)

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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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