In the first and second of installment we examined the evolution of transistor ignition from being a high performance or fleet oriented option, into being a mainstream ignition to help meet the ever tightening emissions regulations of the early 1970s. Although, General Motors was one of the pioneers of electronic ignition and it had the most advanced ignition designs with the most variations, it was the last of the big three to bring its electronic ignition to the mainstream. Nevertheless, GM had the most extensive experience with electronic ignition, so when it went mainstream it brought the most advanced ignition system of the big three to the market – the High Energy Ignition (HEI) system (also discussed in detail by our own Daniel Stern).
GM sales literature for 1975 boasted about the new HEI system.
The HEI system was introduced in late 1974 on some GM cars, and was used across the entire GM product line in 1975. This new ignition had a significantly higher output and longer spark duration, assisting GM meet the ever tightening emission standards. The HEI design team had several objectives for the ignition system. These were:
- A maintenance free distributor, coil and electronics
- Extended spark plug life
- Improved combustion of fuel mixtures by increasing spark duration by 50% and spark voltage to 35 kV
- Improved reliability and improved insulation materials
Several of the design innovations used on the Delco-Remy Unitized ignition were carried forward. The success of the Unitized Ignitions integral design meant that from the beginning it was planned the HEI system would also be an integral design. The advantage of the integral design was that it allowed for testing the ignition system prior to installation in the vehicle, improving quality control and production efficiency. Vehicle installation was also simplified, requiring only connecting the spark plug wires, the 12 volt power supply and adjusting the timing.
The HEI distributor was similar to Unitized design, and continued to use the same basic design for its magnetic pickup that Delco-Remy designed in the early 1960s. The HEI distributor increased in diameter, which was required to prevent cross fire due to the higher voltage. New improved insulating materials were used for the distributor cap and rotor to help withstand the extra electrical stress. The larger diameter distributor allowed for the module to be placed inside the distributor under the cap, rather than outside of it as on the Unitized Distributor.
Most of the HEI system was just an evolution of past Delco-Remy designs, but ignition the module was a revolutionary component. Before we examine the HEI module, it’s important to look at the weaknesses of the previous transistorized ignitions. Due to the high stresses from the extreme conditions that an automotive ignition endure, it wasn’t possible to make full use of the transistors capability in previous electronic ignitions. Unlike electro-mechanical parts (such as ignition points), the transistors used in ignitions were not capable of handling any undue stresses caused electrical current spikes. These spikes can occur when starting a car, in the brief period when the engine started but the ignition switch is in the “run” position. Electronic components can immediately fail under these extreme conditions. Therefore, a significant safety margin well below the components capability was engineered in place. This was typically done through a reduction in power through a resistor. As a result, while transistor ignitions were often more capable than standard breaker point ignitions in most circumstances, the margin overall improvement in performance wasn’t always as big as one might assume.
The 6 cylinder and 4 cylinder distributors had separate coils due to their smaller size.
For the engineers to meet the performance goals required a solution that would allow for the electronics to cope with the electrical spikes. That solution was current regulation. The new HEI module regulated the current to a maximum of 5.5 amps. This prevented the transistors from being damaged from excessive current and allowed for the transistors to perform near their maximum capability.
This shows the current limiting of the HEI module. This is a later model HEI module which was regulated closer to 6.0 amps.
One of the major reasons that an ignition coil has poor high RPM performance is caused by the resistance in the primary circuit. Breaker-point ignitions uses a coil with high primary resistance to limit the current at lower engine speeds, but it comes at the cost of high engine speed performance. The HEI system used a new low resistance coil, with a resistance value of 0.5 ohms (compared to a 2.6 ohm coil for a typical breaker-point ignition). The lower resistance coil also allows for much faster charging of the ignition coil and it can create more voltage with less amperage. To compare, a standard 2.6 ohm coil would require 11 amps to produce 35kV, while a 0.5 ohm coil produces 35kV with only 5.5 amps.
HEI system integral ignition coil design.
The coil was also redesigned to be more like a traditional transformer than the old canister style coils. The new “e-coil” had the primary winding wound around the inside and the secondary windings on the outside, the opposite of a canister coil. This allowed a low primary resistance with a reasonable size of wire. The entire assembly is potted in epoxy to better protect it against moisture and degrading effects compared to an oil filled coil.
This is a comparison of an HEI coil compared to the standard breaker-points coil. Note how much faster the current builds in the low resistance HEI coil. This also shows the current limiting of the HEI module.
The current limiting ignition module is what works hand in hand with this low resistance coil. The module ensures that at low speeds the current is limited to prevent excessive current stress, while the low resistance coil drastically improves ignition performance at higher engine speeds.
HEI has significantly higher voltage than a breaker-point ignition, but its voltage starts to reduce at about 3100 RPM (for first generation module).
The HEI module also had one further revolutionary feature, automatic dwell time control. Unlike past ignitions that had a fixed dwell time, the HEI module was designed to turn on the coil current when there is just enough time for the coil to reach full charge. By minimizing the dwell time to just what is required, this function eliminates excessive power dissipation, which in turn reduces the module operating temperature and increases its reliability.
This is the AC signal from a HEI pickup coil. The module as programmed to determine when to “turn on” the coil charging depending on the engine speed. Note that at higher engine speed the coil is turned on earlier to increase dwell time.
The module turns on the coil current to charge the coil when the pickup coil in the distributor is creating a the slower positive portion of the AC wave form. From this portion of the wave form, the module anticipates the next ignition pulse. The module adjusts its turn-on point so there is just enough time for the coil to charge before the primary circuit is opened. So, the coil turn-on occurs just prior to ignition at low speed and advances toward the previous ignition pulse at high speed (as seen in diagram above). The result was the ignition produced a consistent 35kV of output voltage up to 3100 RPM (where it begins to decrease) and 30 kV of output voltage during cranking with battery voltage as low as 6 volts.
The HEI module has been adapted to many other ignition systems, and can work with a Ford or Chrysler electronic distributor.
The HEI system met all of its design goals and it was the most advanced of all of the ignition systems to come from the Detroit Three in the 1970s. The HEI system allowed for significantly longer spark plug life and wider spark plug gaps, improve starting, reduced emissions through more complete combustion, and reduced maintenance with consistent ignition performance over longer periods. Today, although HEI has long been superseded, it remains very popular to retrofit an HEI module in all sorts of other ignition system, as we saw in tbm3fans’ 1973 Polara. Further, the distributor design has been copied many times over in the aftermarket for countless applications, allowing for simply “one wire” ignition installations on all kinds of engines, including many non-GM engines.
Chrysler was first to offer a mainstream electronic ignition system, but it wasn’t long before this system was further enhanced when it was incorporated into Chrysler’s Lean Burn ignition. Although the ignition was a key component in Chrysler’s Lean Burn System, it also involved several other components. These were a specially designed Carter Thermo-Quad carburetor and numerous sensors for throttle, air temperature, manifold vacuum, and coolant temperature. Controlling this entire system was the Spark Control Computer, which was attached to the side of the air cleaner. Inside the computer were actually two modules, the ignition control module and the program schedule module.
A first generation Lean Burn distributor with the dual pickups.
At first glance the ignition system for a Lean-Burn car didn’t appear much different than that the Chrysler EIS. However, the distributor was significantly changed. The vacuum advance was eliminated and the distributor used two pickup coils. Instead of the slower and less accurate vacuum advance canister controlling the ignition advance curve under cruising conditions, this was job was controlled by the timing circuit in the spark computer. Through the readings the computer obtained from the various sensors the ignition timing could be precisely controlled to help burn lean and cleaner fuel mixtures.
The Spark Control Computer was initially two separate components, the ignition control module and the program schedule module. These were combined into one unit for the second generation system.
Each of the two pick-up coil in the distributor had a specific purpose. One pick-up coil was used for starting the engine and the second was used for when the engine was running. The start pickup uses a fixed timing setting only. Once the engine starts, the “run” coil pickup takes over and it is controlled by the spark control computer which can control the ignition advance almost instantaneously. If the “run” pickup ever failed, the engine could operate solely off the “start” pickup, although the timing would be fixed.
The program scheduler module controls the ignition control module, which in effect can then advance or retard timing as needed.
The Spark Control Computer’s program schedule module determines the optimal ignition timing that is required based on all the input from the sensors. It provides the correct amount of ignition timing required for the engine under its current operating conditions. The other half of the Spark Control Computer is the ignition control module. This controls the ignition’s primary circuit at the coil, just as it did in the Chrysler EIS. The program scheduler alters the timing of when the signal is sent to ignition control module to interrupt the ignition coil’s primary circuit. By controlling the timing of the signal for opening the primary circuit, the Spark Control Computer can advance or retard the timing as required, and can do so much more quickly and precisely than a vacuum advance canister. It should be noted that the spark control computer didn’t have absolute control over the timing advance, as the distributor still used a centrifugal mechanical advance.
The second generation Lean Burn System
Chrysler introduced the Lean-burn System for the 1976 model year of the 400-4bbl engine in intermediate and full-size cars. In 1977 the second generation Lean Burn was released and it became available on all V8 engines. It had a few revisions that made the system a bit simpler. Chrysler eliminated the dual coil pickups in the distributor and went back to a single pickup. It also combined the two modules in the Spark Control Computer to be one unit. And finally the Spark Control Computer was give full control over the timing curve, as the mechanical advance was eliminated from the distributor.
The vacuum advance canister cannot adjust timing as quickly as the Spark Control Computer.
The Lean Burn System did not increase the overall ignition energy over the previous EIS. However, it was the first US-made ignition to offer precise computer control of the advance curve. While previously an ignition system could only control its advance via engine speed, and load, the Lean Burn system allowed for input from eight sensors to determine the optimal timing for more specific conditions, which in turn permitted a leaner cleaner fuel mixture to be burned. The end result was reduced emissions, with less rudimentary external emissions devices. However, as it was later discovered, Chrysler’s idea of mounting the Spark Control Computer on the air cleaner proved to be a poor idea for the primitive electronics within and the system did not hold up well over time. Reliability was definitely not the strong suit of the Lean Burn System, but it still should be remembered for pioneering such advanced technology for the era.
A DuraSpark II system and all the components. It was very similar to Ford’s Solid state ignition, but used a large diameter distributor cap like GM’s HEI.
Ford’s Solid State Ignition introduced in late 1973 was not cutting edge in anyway, being very similar to Chrysler’s EIS. Ford “refined” the ignition system on an annual basis between 1974 and 1976, but only after three years of Beta testing did the introduce the final product in 1977 – the DuraSpark. Ford released two variations of DuraSpark in 1977, DuraSpark I, used exclusively in California and DuraSpark II used for the remaining cars. While each system was similar, there were a few noteworthy differences.
Wiring diagram for Ford DuraSpark II
The much more common DuraSpark II system was very similar to the Solid State Ignition that preceded it, but it had a number of improvements that improved performance. Ford reduced the primary resistance in the resistor wire which increase the primary voltage. This resulted in higher secondary voltage, improved ignition performance and increased overall ignition energy. This in turn helped produce a cleaner burning ignition system. The internal distributor components were unchanged, but Ford increased the diameter of the distributor cap and switched it to male terminals. Like GM’s HEI, the larger diameter was used to help prevent crossfires due to the higher voltage of the ignition system. Ford carried over the same ignition module and coil from the 1976 Solid State System, both of which remained in use for the life of DuraSpark II. Although an improvement over the Solid State ignition, DuraSpark II was not as powerful as the GM HEI system, and did not have advanced features such as an ignition module with current limiting or dynamic dwell. It did however, incorporate some basic timing control, and allow the ignition timing to be retarded when the car was being started, to allow for easier starting.
DuraSpark modules are identified by the wiring block or strain. This is has a blue wiring block, which was used with DuraSpark II. It was the most common and arguably the most reliable module.
Due to the much more strict emissions in California, Ford designed a more advanced ignition system, solely for that market – DuraSpark I. This ignition had the same basic design and components of the DuraSpark I, but had several important changes. First, like GM’s HEI system, Ford eliminated the resistance wire allowing a full 12 volts to be applied to the coil which increased the primary and secondary voltage. Ford also added a low resistance coil, 0.70 ohms and a special module incorporated dynamic dwell. With these changes, the DuraSpark I system was more similar to the GM HEI system, with the exception being that it was not an integral design.
DuraSpark I was short lived. After 1977, only 302 powered models in California used this ignition as Ford was able to make the other engines pass emissions using the less costly DuraSpark II system. After 1979, DuraSpark I was dropped. Further, DuraSpark I proved to be not the most reliable ignition in the field. DuraSpark II, on the other hand, remained in use though until 1986. Ford did make several varieties of modules, some for special applications like high altitude, but most used the common and reliable “blue strain” module. DuraSpark II proved to be a reliable ignition, and today many Ford enthusiasts retrofit DuraSpark II to their older vehicles.
With that, we’ve reached the end of the decade and the end of the series. These last ignition systems represented the most advanced non-computer controlled ignitions (save for the Lean-Burn). GM’s HEI, Ford’s DuraSpark and Chrysler’s EIS all remain commonly used today by the old car enthusiasts due to their improvement over a points ignition and simple, reliable designs compared to aftermarket ignition. In the next decade, computer control ignitions moved to the forefront and each of the Big Three’s ignitions were adapted. The GM HEI System and Ford’s new DuraSpark III system would incorporate computer controlled timing, while Chrysler’s lean burn was upgraded from analog to digital control. All three would work with computer controlled carburetors, knock sensors and oxygen sensors. However, the writing was on the wall, and distributor controlled ignitions quickly became obsolete and eventually would be replaced by distributorless ignition systems that remain in use today.
A special thanks to Daniel Stern for supplying some of the research material on vintage ignition systems
Ugh… Lean Burn. A very neat idea that was a nightmare as it aged. I had the whole system stripped off my 87 Fury and had it converted back to using an earlier version of electronic ignition. When I first got the car, it would stumble and die taking off from a dead stop and after the Lean Burn was removed it drove SO much better!
I will echo Pioneer Fox. I remember how crazy everyone was for Lean Burn when it came out – it really did seem to solve some of the starting and driving problems that had plagued Mopars during the emissions era.
We got one when it was about 5 years old and the car never really ran right. More than once it went into the dealer service bay to diagnose and replace a component here or there. I finally had enough after I was told the car had two burned valves and had the Lean Burn removed and a 1972-era EIS put in its place.
This was an interesting era with a lot of change. I had a decent working knowledge with points systems and later became conversant with Ford’s EEC-IV of the 80s. But these early electronic systems made my eyes glaze over and in those pre-internet days never took the initiative to understand them and work on them myself. Perhaps this was one reason I owned but a single car built between 1972-1982.
Kudos on this deep dive into ignition systems!
My parents had a new ’78 LeBaron with the 318 Lean Burn. Gutless as H,
(2.45 axle didn’t help), knocked and pinged all the time, and for the first few months would leave you stranded. Always the same pattern, intermittent misses at first, followed by a total conk-out. Sometimes it would restart after a cool-down.
One time it was a bad ground wire for the computer, other times I can’t remember. It wasn’t just that, the whole car was a disaster, a wheel bearing even failed and front wheel flew off!
The concept of Lean-Burn was good, execution not so much. Unfortunately the system didn’t prove to be very good despite the potential. But like I said, it was quite advanced for it’s day. I just think that Chrysler was so hard up for cash at the time, it probably didn’t invest as much in the engineering as it should have.
For the Ford systems, EEC was not actually the ignition. EEC, Electronic Engine Control, was Ford’s name for it’s various versions of computer controlled engines, and involved more than just the ignition. There were numerous versions of EEC. Dura Spark III was used with EEC-III and later EEC-IV saw the introduction of the TFI igntion – Thick Film Ignition. TFI used an highly efficent e-coil and also used an integrated module.
As for Chrysler, it is my belief that by the mid 1970s that company had been so hollowed out that it was no longer capable of the level of engineering necessary to remain competitive. I think there were still some good engineers there who had really good ideas, but they had zero support from anywhere else in the organization. After about 1970 Chrysler was one example after another of “great idea, bad execution”. The 1981 Imperial with its fuel injection may have been the ultimate sign of this rot. That the L and K body cars came out as well as they did is a miracle – and even then there was a big assist from the proven guts of the Simca.
Chrysler of 1979 was like the old alcoholic lawyer who still thought he could win trials like he could 30 years earlier but was no longer even remotely capable. Reputation and reality are not always the same thing.
I’ve had the (dis)pleasure of working on many of these systems.
To me the GM HEI was a positive step in electronic ignition evolution, as long as heat conductive grease was under the module. Basically everything in a neat package.
The Dura Spark system was a distant second.
The Lean Burn and Ford’s EEC-II (with or without feedback) were ABSOLUTE garbage.
I found the EEC-IV to be a very reliable system.
Such are the joys of owning and/or repairing cars.
And of course the less said about the Prestolite system adopted by AMC the better…
Thank my lucky stars I never was exposed to it.
During this time, what was AMC using?
In late 1974 AMC adopted a Prestolite made system, which they called BID (Breakerless Inductive Discharge). It was a variation of the Prestolite electronic ignition used on 1974 International Harvester engines. The ignition system was not designed in house and in itself was nothing revolutionary. Like the Chrysler and early Ford systems, it used an external Electronic Control Unit and it offered little energy increase over a breaker-point ignition.
The big difference was the design of the trigger mechanism inside the distributor. The Prestolite distributor was not like Big 3 designs, which used a magnetic pulse type design that produced an small A/C current. The Prestolite distributor consists of a trigger wheel with the same number of legs as cylinders and a sensor assembly. Its sensor, which is a small coil wound of fine wire, receives an AC signal from the electronic control unit. As the leading edge of the sensor wheel leg enters the sensors electrical field, it cause a reduction in the sensors oscillation strength. The continues to diminish until it reaches a predetermined level which triggers the ignition. Once the leg passes the sensor returns the sensor oscillation strength to normal.
In 1978, AMC abandoned the BID system and adopted Ford’s DuraSpark II, but used a small diameter cap. It also later used GM HEI on some engines as well.
Here is a picture of the internals of a Prestolite distributor: Note the trigger wheel and its legs that pass by the sensor.
The Prestolite system was actually designed by Holley. The trigger method is actually called pulse inductance the same principle as used in some metal detectors and the coils of wire in the road that control traffic signals.
On (most) carbureted cars, the air cleaner housing is a large and relatively heavy item that is attached to the car via a single long, spindly, 1/4-20 bolt. I can’t begin to understand why Chrysler engineers thought it would be a good idea to attach the ignition computer to that.
Eh?
Vibration-induced mechanical failure was not a significant problem; heat was, with the module right atop the stove. Chrysler apparently knew this; at least some police cars had the modules in a cooler location, with underhood configuration otherwise substantially identical to civilian models.
Other problems with the system included the primitive nature of electronic components affordably available at that time, mechanics’ unwillingness to update their knowledge and skills and diagnose and service the system correctly, and—more broadly—the fact that Lean Burn was the wrong answer. Fuel injection was the right answer, and the whole of the US auto industry fully well knew that by 1975. But they were involved in a cynical effort to kill vehicle emissions and safety regulation, which they viewed as nothing more than a needless, pointless, passing fad. They invested a whole lot of money and effort into fighting each and every provision of each and every regulation. If that money and effort had been put into the cars instead, results would’ve been much nicer (viz Bosch D-Jetronic and then K-Jetronic, for two examples), but cheap and nasty compliance was one of their primary tools in the war against regulation. “Oh, gosh, gee, Mr. and Mrs. Carbuyer, you say your new car runs poorly and gets lousy gas mileage and won’t stay fixed? Gee, »tsk« what an awful pity. Not our fault; the Government made us do it. Guess you’d best run get busy writing to Congress.”
Okay, so they knew (for whatever reason) that the air cleaner was not the best place to put a computer, but they did it anyhow, unless you were a cop. I suppose it probably saved 11 cents of wire per car.
Fuel injection made for smoother operation, but was still fairly primitive. A 1975 Volvo 3 liter had about the same HP as a 5.2 liter Dart, but they got about the same MPG.
Sorry, Evan, I must’ve misunderstood you. I took your mention of the single 1/4″-20 air cleaner stud as an allusion to vibration (and thence vibration-induced failure of the Lean Burn module).
Fuel injection did a whole hell of a lot more than make for smoother operation. SAE papers and SAE Journal articles of the time go into great and lengthy detail on the impressive improvements to starting, driveability, fuel economy, emissions, durability of tune, etc—notably with regard to the 1976 Cadillac Seville.
As for Volvos, the ’72 greenbook says a carbureted 164 is in correct tune at 2.5% CO in the exhaust at idle, while a fuel-injected 164E is in correct tune at 1.5%. That’s a 40% reduction in carbon monoxide and more horsepower and better driveability and (etc).
Fuel injection was still fairly primitive in 1975…? Uh, sure, compared to a fuel injection system of 1985 or 1995 or 2005. Compared to a carburetor? Not even close; the ’75 fuel injection trounces a carburetor from 1975 or 1985.
Electronic fuel injection really wasn’t practical and durable until digital computer chips became available that could take automotive heat, vibration and voltage spikes. The technology simply didn’t exist at consumer prices until the mid-80s.
I once tried to cure a 1970-ish VW Squareback with Bosch D-Jetronic analog EFI that was only about ten years old. It was a nightmare that I ultimately gave up on. Analog components drift as they age, so it was totally out of whack. (Bits don’t drift.)
Nice link to “Manifold Destiny”. A stove indeed.
You and I would probably quarrel over what constitutes (and constituted) practicality, but I’ve got seeds and plants to put in the ground, so I’ll keep it to this: ’70s EFI wasn’t as good as ’80s-’90s EFI, but ’70s EFI was better than ’70s-’80s carburetors. Components drift? Yep, and they’re also replaceable. Old radios work a lot better when their capacitors and resistors are replaced; the same is true of a D-Jetronic brain box. Often the problem with a D-Jet car that wouldn’t run right was an accumulation of previous-owner and previous-mechanic foulups so thick as to require starting over from scratch.
Yes, certainly ’70s EFI was superior when it was new, it just didn’t age well. But by the time that would have mattered in most cars it was junked for other failures of longevity, such as rusted sheet metal. Most cars weren’t expected to last much more than ten years in those days.
Even digital electronics don’t last forever but unlike mechanicals they can be nearly impossible to restore or replace. About all you can really do is hope to find a junkyard board that still works. They get fewer as time goes on. Worn-out electronics is an issue that looms over the old car hobby.
I think both Mike and Daniel make great points. While I think that Daniel is on the money about EFI would have solved a lot of issues had it been adopted earlier, I can’t say that the systems from that era were all that great in terms of longevity or reliability. This is especially true when compared to some of the good carburetors of that time, like the Q-Jet or the Motorcraft 2100.
One American make did have EFI in this era. Cadillac did adopt EFI with the Cadillac 350 Olds powered Seville, but it was also optional on the 500 and 425 Cadilllac engines. The EFI engines made more power and I am sure burned cleaner than the carburetor versions (although they still used HEI ignition and catalytic converters). It’d be interesting to compare the emissions for each version of the engine. These early Cadillac EFI systems weren’t known for their reliability and personally I’d take a Q-jet over that system any day, for the better reliability and simplicity.
Chrysler Lean Burn wasn’t the best solution, but the concept of computer controlled timing based on multiple sources of data was adopted by all cars, and did become mainstream even with EFI. So like I said, it does hold some historic importance. I agree with Daniel that the primitive electronics and the harsh environmental conditions resulted in it being a poor system though.
I personally have no issue with these late 1970’s engines that run a carb and decent electronic ignition. As an old car owner, I’d take this setup any day over a Bosch EFI setup – but that’s me. And I can say that as some one who literally just drove a never been touched 43 year old HEI and carb setup tonight (the carb does need a rebuild though). Where things jumped the shark for me, was the electronic carbs. Just absolute half-assed solutions that never should have happened. GM had Digital EFI on Cadillac in 1980 (a basic TBI system). There was no reason it couldn’t have been rolled out shortly thereafter across the board, but they chose to run feedback carbs that was just enough to pass the sniffer test. While Chrysler and Ford ran these carbs too, GM was the worst, using them all the way to 1990, and ironically one of the last cars was a Cadillac!
Here’s a picture of one of the D-Jetronic’s two circuit boards. They both look like this. Not something I’d like to restore. (Though there’s at least one site with diagrams, scope traces and everything if you’re truly masochistic enough to try.)
Sometimes technology that’s ahead of its time is ahead of its time for a good reason.
I’d be on super thin ice saying anything akin to “Meh, what’s so daunting?”, for a good collection of reasons including that I’m a menace with a soldering iron. But I know people, non-masochists, whose eyes light up at the notion of a project like this and can
play a guitarwield a soldering iron just like a-ringin’ a bell. That same site you linked also has a dissertation on the manifold pressure sensor, which is highly application-specific.Ahead of its time? Well…h’mm. The Bendix Electrojector in ’58 Chrysler products was surely ahead of its time in all the good and bad ways, but I don’t think D-Jetronic was ahead of its time. It was a first go, a start at the art, with all the implications that entails both on the design-specify-build side (component suitability, circuit and hardware configuration, etc) and the service-maintain-repair side (steep learning curve for anyone who even thinks of touching it, etc).
After over 40 years a penny just dropped. I always wondered why Ford went to those
smaller-diameter, unpainted aluminum air cleaners starting in ’77. FoMoCo buffs will know what I mean. I just now realized it was to clear the bigger distributor on the Dura-Spark. Only the 460 didn’t get them, I guess the 385 series had enough clearance for it.
That was my thought as well Roger. FWIW, on my 400 that I built, it now uses a DuraSpark distributor with a HEI module. It clears the OEM air cleaner, but I also have slightly more than stock clearance due to the Edelbrock intake being slightly taller than a stock manifold. I suspect it wouldn’t clear if I used the OEM manifold.
Well and the aluminum air cleaner represented something like a 50% weight savings over the old steel units. The cams also were at the point by that time that most of the engines just couldn’t ingest near the same volumes of air as their older brethren.
VW was still using points distributors right up until the 1980 model year, but used k-jetronic FI on water cooled models starting in ’77 some ’76 Scirocco’s (S models) got it earlier. Apparently the FI was efficient enough that points could still be used and pass emission standards. This has been a really interesting series, great read.
Thank you for your kind words. I think this goes to show there were two approaches to dealing with emissions in the 1970s. Using a carb, with cleaner burning ignition (and a catalytic convertor in most cases) or FI with a more basic ignition. Regardless by the mid 1980s most went to EFI and computer controlled ignition systems as emission standards continued to rise.
Up here in Canada we had looser emission standards and until 1988 and many of our cars still used mechanical carbs and non-computer controlled ignition systems. That meant our cars often had no ECMs in them even in the mid 80s.
Very informative, Vince. This has been a great series.
So my ‘79 Futura had the DuraSpark II.
I only ever had one problem with it. The Ignition Module failed on me in a weird intermittent way. The car would start running impossibly rough, then cut out. I’d let the car cool off, and it would start again and run fine.
Eventually I got a new box, mounted it and plugged it in, and never had a problem with it again. The 200 cu in Six had a little one barrel carb that gave me some trouble (screws kept coming loose) until I fixed that with some Loctite 232.
I think I replaced the rotor and cap once when I did the wires and plugs, but after reading this, I probably didn’t have to do that.
Years later, my then 9 or 10 year old ‘88 T-Bird (5.0L V8 with EFI) acted the same way on me, but by then I imagine it was a different ignition system all together. The second time it let me down, I called for a tow, and by the time the flatbed showed up, I was able to start the car and drive it onto the tow truck myself. Had it fixed, and traded the car in on a ‘97 T-Bird shortly thereafter. My 5.0 had 236K on the clock when I let her go. The only car for which I shed a tear upon trading it. I imagine I’ll feel the same when it’s time to let the Mustang go. 😢… but not yet… 😀
Thanks Rick, I appreciate your words. I had experienced a similar type module failure on a newer computer controlled HEI ignition on my Oldsmobile. It only would misfire when it got hot but was fine otherwise.
Your later model T-bird would have used. TFI ignition which had a module mounted on the distributor itself. These ignitons were computer controlled but still required a module to work properly. So it could have also been the failure point on that car too, despite being a different design.
In 1980, I was about to head off to grad school and needed a new car. My 1975 Pontiac Astre, the first car I ever owned, had failed on me (yes, as a matter of fact, it DID overheat and warp the cylinder head—how did you know?).
Anyway, my Dad and I shopped for something cheap and sort of reliable and came up with a 1976 Mercury Cougar XR7. A friend of my Dad’s who had been in the car business suggested something to me: “Be sure you get a spare ignition module, wrap it in bubble wrap and keep it in the trunk. One morning you’ll come out and put the key in the ignition and nothing will happen. It will just be dead. Put that spare ignition module in and you’ll be fine.”
I did just as he said, and sure enough, a couple of years later, that exact scenario occurred. I put in the spare module and drove away. The module looked just like the Motorcraft item pictured in the post.
I didn’t much care for the Cougar, given that it was a malaise-era brougham-y coupe with a vinyl Landau roof and an automatic, but it was reliable enough (if you had a spare ignition module), and had a bench seat, which my then-girlfriend and now wife really liked.
Interesting series — a lot of this I don’t well understand, so I appreciate the primer!
I’d be interested to see a piece on the ubiquitous European combination of the time: electronic ignition combined with Bosch K-Jetronic injection. That was often the top-of-the-line setup until European markets started getting serious about emissions controls, at which point electronic L-Jetronic injection and its various descendants became the norm.
Thank you, I am glad you found it interesting. As for the Euro stuff, that’s not something I have a lot of knowledge or resources about, but I agree it would be interesting.
Basically, a number of manufacturers basically did a belt-and-braces approach with K-Jetronic, which was a mechanical fuel injection system (also known as CIS, for Continuous Injection System — the K was from the German word for continuous), but was married to various electronic bits. I don’t know much about the electronic ignition system, but there was also the Bosch “Lambda Sond” O2 sensor feedback system.
The first GM “computer” ignition system came on ’77 Toronados. It was called Misar. This is roughly comparable to the Chrysler “Lean Burn” system–primitive electronic spark advance. Spark timing was based off of a crankshaft position sensor, with electronic “centrifugal” and “vacuum” advance. Most of the electronic bits were safely installed in the passenger compartment away from heat. Interestingly, the GM publication describing the system refers to it’s use of a pair of “vacuum tubes”.
What they meant, of course, were the vacuum HOSES routed through the firewall; one attached to manifold vacuum, as a load-sensing system for use by the spark advance system. The other was “open” to atmosphere as a barometric pressure source.
The GM publication I have does not refer to Misar use in ’78; and in ’79 the Electronic Spark Timing (EST) system was in place.
Misar was doomed for various reasons, among them the fact that they were installed on few vehicles. One or perhaps two model years, of a single upmarket, low-volume carline. Dealership and independent shops wouldn’t have seen enough of these vehicles to make proper and thorough technician training worthwhile.
I am not sure, but I think that Motorola made the electronics for Ford’s various electronic ignition systems. Some time in the mid-1970’s, Motorola began selling retrofit electronic ignition systems under their own label. I bought one for my Mom’s 1972 Maverick for only $20 at a Zayre department store where it was on sale for half off. I found out why they were on sale when I got it home. The four (4) wires exiting the potted electronics module were nicked just above the potting compound. I returned it for exchange, and the young clerk (a fellow teenage gear head like myself) allowed me to open the box to check to see if the wires were O.K.. I think I went through over half a dozen boxes before I found one that had intact wires exiting the control module! The kit had a small pickup coil assembly that replaced the breaker points and an assortment of adapter plates, to mount the coil to the distributor. The control module was screwed to sheet metal under the hood (ours was mounted on the driver’s side shock tower), and power came from the ignition coil. It worked so well that we kept that system installed until the motor finally threw a connecting rod and the car went off to the junkyard five (5) years later!
Here’a link to the Motorola kit on eBay. Mine was packaged in a box for retail sale, and this one appears to be from dealer stock or for professional mechanics to install, but it has all of the same pieces as my $20 version back in the day!
https://www.ebay.com/itm/126240512503?chn=ps&norover=1&mkevt=1&mkrid=711-213727-13078-0&mkcid=2&itemid=126240512503&targetid=4580153139072956&device=c&mktype=&googleloc=&poi=&campaignid=437225723&mkgroupid=1224856224320864&rlsatarget=pla-4580153139072956&abcId=9300907&merchantid=51291&msclkid=0d9c4b512e8e15ed937d2d4d9d3a5c59
Hello, I’m hoping someone has knowledge of an issue I had with my ’78 T/A last week – it has the stock HEI set-up. When I tried to start the car after running errands, my starter was acting tired and through trying several times I smelled burning wires and almost fried my dash. When I took everything apart I found the wire that got hot was the BrW 24 gauge single strand stainless steel wire running from the ignition switch connector to the bulkhead connector, most likely caused by an internal short in my alternator (the wire is apparently called the exciter wire because when the key is on, a low voltage signal travels from the switch to the alternator post, telling it to start charging); however, the larger gauge wire on the engine side to the alternator is undamaged.
Can anyone here corroborate what I found out about that BrW wire? I’ve attached pics, in multiple replies as it seems I only get one at a time, and most importantly, I need to know why GM used stainless steel for that wire, and where to source some replacement – I don’t care if the color matches, but so far all I can find is wire without insulation. I’m thinking stainless steel was used for it’s resistance values, but I can’t be sure…the wire is 50 inches long, give or take an inch…any help would be appreciated!
I buy Genuine GM service manuals for every vehicle I own. Almost all of them have come from eBay, used, at very advantageous pricing.
I have gotten service manuals on DVD; which works pretty good except the files are in .pdf format, and the files are so gigantic that the scroll-bar is useless. A deliberate touch of the scroll bar moves fifty pages instead of two or three. OTOH, the .pdf files can be searched which is sometimes handy.
Anyway, the answers you need are in the service manual set for your vehicle; and readily available on CD-ROM or DVD if not the actual paper books.
For example:
https://www.summitracing.com/search/department/books-videos-software/year/1978/make/pontiac/model/firebird/brand/bishko-automotive-literature/part-type/reference-books?fr=part-type&SortBy=BestKeywordMatch&SortOrder=Ascending&keyword=Service%20manual
I do have the service manuals, along with Haynes manual and a stack of articles, but the electrical sections are only basically helpful, without enough detail, with the exception of the wiring diagram, but even that doesn’t why that isolated wire is different from the rest…
…second pic:
…third pic:
…and a pic of the alternator post, which is wiggly loose because the plastic bushing has burnt and cracked…the thing was installed just last fall!
I await the next installment in this series with breathless anticipation! The next steps of course, were Throttle Body Injection (TBI) in the early 1980’s, to be followed by true Multi-Port Injection by the end of the 1980’s. As computing power increased and high-voltage transistor technology improved, the distributor disappeared in the late 1990’s, followed by integration of the ignition control, fuel injection controls and transmission controllers into a single control computer. The final step was coil on plug systems when the spark plug was moved from the side of the cylinder head to the top of head, when multi-valve cylinder heads became common place. Traditional OHV V8’s got a dedicated coil for each cylinder, with each coil mounted on the valve cover, but with a short length of high tension wire to connect the spark plug to the coil, since the side-mounted spark plug made mounting the ignition coil directly on the plug itself impractical.