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.

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)


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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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