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.

EFI Aftermath

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

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

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

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

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

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

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

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

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



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Kennedy, U.S. Patent No. 2,018,159, “Electrical Fuel Injection System for Internal Combustion Engines,” filed 20 June 1934, patented 22 October 1935; Harry Walton, “How Good Is Fuel Injection?” Popular Science Vol. 170, No. 3 (March 1957): 88–93; Gary Witzenburg, “Driving the 1980 General Motors model,” Popular Mechanics Vol. 152, No. 4 (October 1979): 97–99, 236–241; Tom Yates, “How GM’s throttle body fuel-injection system works,” Popular Mechanics Vol. 155, No. 2 (February 1982): 66, 68; Anthony Young, Chevy Classics 1955 • 1956 • 1957 (New York: Barnes and Noble Books, Inc., 1999); and Richard Zechnall, Günther Baumann, and Hermann Eisele, Robert Bosch GmbH, “Closed-Loop Exhaust Emission Control with Electronic Fuel Injection,” SAE Technical Paper 730566 (Warrendale, Pa.: Society of Automotive Engineers, 1973).

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

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



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  1. Great article

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

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

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

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

  3. Ridiculously comprehensive, as usual!

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

    Great article, thank you

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

  9. Great article. I’m wondering, if VW was forced to adopt D-jet on the Type 3 for CA emissions, why did the beetle and bus stay carbureted through 1973/1974?

    Also, a small nit-pick. In the photo of all the D-jet components you have an ignition coil labelled as a fuel pump

    1. The Type 2 was a light truck, and as such I think initially in a different category. The Type 1 was probably able to get by in 1968–1969 by switching to the 1500 engine with the throttle positioner device; the Beetle was about 300 lb lighter than the Type 3, and the larger engine probably did better than the 1200 or 1300 on HC and CO emissions as a percentage of total exhaust volume, even though its total emissions per mile were higher. The federal standards were also more generous for engines under 1,600 cc, and I think they ended up temporarily preempting the California standards for 1968–1969. Once that changed, and the standards switched to emissions per mile, some versions of the Beetle and Type 2 did end up with air injection or EGR.

      Thanks for the correction. I fixed that and another error in the photo captions.

      1. That makes sense, thanks! Though I’m not sure about the Bus being a light truck, at least in all cases. A single or double cab truck would be, as well as a panel van (all rare at this point due to the chicken tax). But the majority of Buses in the US at this point would have been regular passenger models (which VW called Station Wagon often), or campers. Would those have been classified as trucks?

        1. Quite possibly: The conceptually similar Ford Econoline and Corvair-based FC95 models were treated as trucks and sold through Ford and Chevrolet truck dealers, as were the Ford Ranchero and Chevrolet El Camino, although those were even more obviously car-based and probably used more as cars than pickups. As we’ve subsequently seen, the real definition of “light truck” is “whatever de minimus pretense will get us special dispensation on motor vehicle regulations.”

          How that applied in the sense of the early California exhaust emissions standards is less clear. The problem I ran into is that California does not, so far as I’ve ever been able to find, maintain any unified searchable repository of superseded laws and regulations — this is in contrast to the feds, where that stuff IS online, it’s just very difficult to find any of it unless you already have a specific reference.

          However, judging by VW’s actions, it appears that they figured they could get the Beetle under the California limits by switching to the 1500 engine with the throttle positioner, that they weren’t initially too concerned about the Type 2, and that their biggest problem was figuring how how to get the Type 3 to comply with the California limits of 275 parts per million (ppm) hydrocarbons (HC) and 1.5 percent carbon monoxide by volume.

          The other day, I did find an excerpt of a transcript of a 1967 Congressional hearing where a VW engineering official said they’d decided they could use an air injection pump, but as best I could determine, they didn’t actually do so until the early seventies. The federal regulations that took effect for 1968 provided more generous limits for smaller engines:

          • For engines over 50 cu. in. (0.8 liters, but under 100 cu. in (1.6 liters): 410 ppm HC and 2.3 percent CO
          • For engines between 100 and 140 cu. in. (1.6 and 2.3 liters): 350 ppm HC and 2.0 percent CO
          • Engines over 140 cu. in. (2.3 liters): 275 ppm HC and 1.5 percent CO, the limits previously established by California.

          The initial federal regulations, which preempted the California ones for 1968 and 1969, applied to motor vehicles and motor vehicle engines greater than 50 cu. in. displacement, but did not yet apply to motorcycles or to commercial vehicles above one-half ton. All that eventually changed, but the intersection between federal and state law effectively bought VW more time to sort it out. So, the Type 2 eventually got an air injection system, but I believe not until 1972.

      2. I believe the 2nd row of the component photo caption also needs to be corrected. Here is what I believe is correct, “Second row, left to right: throttle-valve switch, fuel pressure regulator, crankcase temperature sensor, cold-start valve, cylinder head temperature sensor, aux-air regulator”. I checked this against the component images from “Volkswagen Fuel Injection Technical Manual” by Henry Elfrink

        1. The caption was still wrong, but not quite like that. As you may surmise, the photo as I got it from Bosch was not labeled, and so I tried to decipher it by comparing it to the line drawings in the labeled diagram, which turned out to be somewhat misleading. (For instance, the line drawing shows the auxiliary air device housing, not the actual valve inside of it.) What I SHOULD have done was compare it to the Bosch D-Jetronic service manual, although that often shows the components from different angles that make them harder to identify. In any case, the top left component is in fact the fuel pump; the top right component isn’t shown in the service manual or diagrams, but it is, as you correctly noted the other day, a Bosch ignition coil. On the second row, the thing at the far right is the auxiliary air valve, as you say. Of the three objects to the left, the silver thing in the middle is indeed the cold start valve. The brass items flanking it look to be temperature sensors; comparing them to the line drawings in the service manual, I’m reasonably sure the one on the left is the intake manifold temperature sensor, whose shape is more distinctive, which means the one at the right is the head temperature sensor. Since there is a cold start valve, the components are for a later system, so there’s an intake manifold sensor rather than the crankcase temperature sensor on early systems (which did not have the cold start enrichment valve and suffered for it in cold weather). I think that should be right now.

  10. Yeah that makes sense, very informative, thank you. I knew there was some weirdness with getting things classified as trucks post-CAFE (like the PT cruiser being classified as a light truck due to load floor space despite being a tall Neon), but I didn’t know it went back so far. According to my bay window Bus Bentley service manual (1969-1979) ” All the engines covered by this Manual have closed PCV (positive crankcase ventilation) systems. Single carburetor engines have a throttle valve positioner — supplemented, on 1971 models, by a throttle valve damper. Dual-carburetor engines have the throttle valve damper only. Fuel injection engines have a deceleratior air enrichment valve. Exhaust gas recirculation is used on 1973 and later models. An air injection system for exhaust afterburning is used on 1973 and 1974 dual carburetor engines. Some fuel injection engines have an catalytic converter for emission afterburning, and the 1979 and later California models have an oxygen sensor system.” This seems to bolster your supposition

    1. The trap I’m trying to avoid is conflating the way California and federal law currently distinguish between passenger cars and commercial vehicles with how it was established in the sixties, which may not necessarily be the same. (I really wish I had either copies or a coherent summary of the original California rules, but it seems like the only way I could get that would be to go to the central library and see if they still have physical copies of the bound volumes with the old statutes, and I’m not sure those include regulations.)

      The other consideration with the Beetle is that it may have been enough lighter than the Type 3 to fall into a different inertia weight class. The emissions tests were done with a 7-mode dynamometer test, simulating road load at 50 mph. The amount of weight added to the test flywheel and chassis dyno was based on the estimated loaded weight of the vehicle, but rather than being progressive, it was divided into tiers. For the federal regulations, a loaded weight (which was shipping weight plus 400 pounds) of more than 1,750 lb but less than 2,250 lb got 2,000 lb on the flywheel and 1,500 lb on the dyno; if loaded weight was over 2,250 lb (even by a pound) but less than 2,750 lb, it got 2,500 lb on the flywheel and 3,000 lb on the dyno. So, the Type 3 being in a higher inertia class meant that it had to work significantly harder on the dyno when undergoing certification testing than the Beetle did; you can see how that would have put it in a less-favorable position.

      That still doesn’t address the Type 2, which was also obviously heavier than the Beetle. I don’t think the Type 2 was exempt under federal standards in 1968 or 1969, although with the 1500 engine, the more generous federal limits for CO and HC presumably let it get by. Whether it would have been required or able to comply with the California rules for 1968 or 1969, I’m still not sure, although obviously it ended up being a moot point.

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