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The Chrysler Lean Burn engine control system: first onboard auto computer

The Lean Burn system was an early spark advance control system (introduced in 1976 and continuing to the 1980s) that was troublesome due to the nature of the contemporary electronic components, as well as the yards of vacuum hose and competent mechanics needed to keep it working. Materials technology eventually caught up, but many mechanics did not, and many owners simply switched to conventional carburetors.

Auto part Engine Automotive engine part Diagram


Chrysler boasted, "Electronic Lean-Burn System, with its electronic spark control, is one of the most important developments in engine control since the 1920s and early 30s, when manual spark control was replaced by the automatic spark advance. Eight sensors and an electronic computer combine to adjust spark advance correctly for all driving conditions." (This turned out to be true in the long term; every car currently made uses electronic spark and fuel control.)

Auto part Technology Electronic device


The second generation system, described below, came out a single year later, in 1977. It was similar but integrated electronic ignition and eliminated the centrifugal advance flyweights and one of the two pick-up coils from the distributor. In 1978 it was expanded to be used on most Chrysler V8s. By this time, Chrysler's related inventions - electronic ignition and the electronic voltage regulator - were already standard.

Auto part Diagram


The 1978 description of the second generation notes, "This new computer consists of one integrated circuit board which computes all vital information for controlling the ignition system. It eliminates the starting pick-up coil and the centrifugal advance flyweights from the distributor and performs these functions electronically.
The spark-control computer also includes the electronic circuitry for the electronic ignition-thereby eliminating the separate control box for the electronic ignition."

Auto part Automotive lighting Diagram


Randy Miller wrote: Most people did away with Electronic Lean Burn, I think, because it was new technology and fear of "that electronic black box."

Back then, mechanics were being introduced to electronic devices never seen before in the automotive industry. I, on the other hand, was into electronics, and it fascinated me to know what was in that black box. I studied the system, learned how it worked, and eventually had local mechanics call me whenever a car came in with this system. Most of the problems turned out to be normal ignition or fuel problems, but, because it had "that black box," it must be the problem.

As years have gone by, I have found some problems with the computer itself. For example, I started my 1977 Chrysler Newport (with the original 400 Lean Burn engine) on morning and it was running fine and then for no reason it died. I started it again only to find it died a few second later. I traced the problem to the spark computer.

I took it apart, digging out the potting silicone to reveal the circuit boards. After some cleaning, I found a bad solder joint on one of the circuit boards. I got to thinking, what is the biggest problem with electronics in this application? Heat and vibration.

I retouched all solder joints, replaced the electrolytic capacitors, and repotted the boards back into the housing with potting silicone. The silicone was not cheap, but it put the unit back the way it was produced. After reinstalling it, the engine started and ran fine.

If Chrysler had mounted the unit on the body instead of the air cleaner as they did in production, I think a lot of these problems could have been resolved.

Chrysler broke the ground for the first computer controlled engine and I think they would not have had the problems they did back then if they would have taken a few extra steps. All car engines are now computer controlled thanks to their engineering team. Heat and vibration don't mix very well with electronics.

Yes, my old Chrysler still runs with the original ELB system!

Chrysler's Electronic Lean-Burn System, with its electronic spark control, was cited as providing:

  • Smooth engine warm-ups
  • Improved engine performance
  • Improved smoothness of engine operation
  • Controlled emissions-even before they reach the exhaust system
  • Less emission-control "hardware": several responsive sensors feed information to an electronic computer to keep the lean-burn engine performing efficiently.

The system measured:

  • 1. Engine speed (r.p.m.). As engine speed increases, spark plugs must be fired sooner for the engine power and efficiency needed. This sensor reads engine speed and signals the computer to adjust spark timing accordingly.
  • 2. Engine load. This sensor signals the computer to advance the spark for optimum fuel economy at part throttle.
  • 3. Throttle position. This electronic sensor reads accelerator pedal position and signals the computer to advance the spark under conditions when speed and load alone do not give the correct signal.
  • 4. Speed of throttle movement. This sensor signals the computer to advance the timing briefly in anticipation of the desired acceleration. The faster the acceleration, the longer the duration of extra advance. There is no lag.
  • 5. Air temperature entering the engine. As outside air enters the engine, its temperature is monitored by a sensor which signals the computer to advance the timing at cooler temperatures to enhance fuel economy and retard it at warmer ones to protect against destructive detonation or pre-ignition.
  • 6. Engine coolant temperature. This sensor tells the computer to limit spark advance during engine warm-up while the choke is on. This helps control emissions.
  • 7. Carburetor throttle open' or closed. This sensor operates a timing counter which remembers how long and how often the throttle is open or closed. It allows full spark advance at highway speeds but in city driving spark advance is modulated to control exhaust emissions.
  • 8. Engine starting. This sensor tells the computer when the engine has started and advances the timing for about one minute to cut down on engine stalls.

The electronic spark-control computer responds to data from all sensors and instantly adjusts the timing of sparkplug firings. Since conditions are constantly changing, the computer is constantly making instantaneous adjustments in spark-plug firings.

This second-generation spark-control computer consists of one integrated circuit board which computes all vital information for controlling the .ignition system. It eliminates the starting pick-up coil and the centrifugal advance flyweights from the distributor. Information for these functions is programmed into the spark-control computer and is performed electronically. The electronic circuitry for electronic ignition is also contained in the spark-control computer.

Examples of the system in operation:

1. The engine is cold. The coolant sensor tells the computer, which retards the spark so the engine isn't putting out a lot of pollution while the choke is on.
2. The engine coolant warms up. The sensor reports to the computer and the spark is advanced.
3. The engine is started in the morning and the car is driven away. Sensors tell the computer to provide spark advance to get you going.
4. Driving up a hill or pulling a trailer. The engine load sensor reads manifold vacuum and tells the computer whether the engine needs less spark advance to prevent detonation when pulling up the hill-or more spark advance going down the other side. Responsive spark timing does the job.
5. Driving on an interstate highway. The spark is advanced.
6. Rapidly depressing the accelerator. The sensor signals the computer to instantly advance the spark for more power to accelerate the car. There's no lag in spark advance like you get in ordinary engines.

The invention

The patent was granted in August 8, 1978, listing Gordon Fenn as the inventor. Marc Rozman told us that Gordon Fenn had come up with the system very quickly, and had also worked on substantial improvements to the 1980-81 Imperial electronic fuel injection system (after its introduction, to make it workable on vehicles in the field).

Auto part Engine


According to the patent, signals used to control spark timing included "a throttle advance signal, a programmed vacuum advance signal, a break-idle advance signal, an engine start advance signal, an engine speed advance signal and a fixed timing signal. These signals are algebraically summed together to develop a resultant spark timing signal representing desired spark timing. Individual signals are derived from transducer circuits which are responsive to various engine operating and/or ambient conditions."

The throttle advance included both throttle position and rate, increasing advance as the throttle opened; it was attenuated as the ambient air got hotter.

"The break-idle advance signal provides momentary advance when the engine throttle is displaced from the idle position. The engine start advance signal provides advance for a short interval after the engine has been started. The engine speed advance signal provides increasing advance as the engine speed increases. The fixed timing signal provides fixed timing which is used to adjust the basic timing for a given set of engine operating conditions. The control system is particularly advantageous when used in an engine which uses a leaner fuel-air mixture (17-18:1, for example) in comparison to presently used mixtures (15-16:1). Improvement accrues by way of reduction in exhaust emission products and better fuel economy."

An electronic feedback carburetor was used in 1979 on California cars with the one-barrel 225 and automatic. A digital microprocessor was included in 1980, replacing the analog system used in 1976-79. In 1980, a detonation suppressor system was also used on California V8 cars. The computer gained an adaptive memory system in 1982 for some four-cylinder cars.

Bill Wetherholt wrote:

Lean Burn was the start of the computer age. We had a 1977 Chrysler New Yorker, the first year for Lean Burn. It was a great car for the first year. But she was on the way to work one morning, and it just quit, the Lean Burn module had burned out. They replaced it with a rebuilt one, and the car never ran right after that. Once, I was trying to pass this guy in a Cadillac, he was going about sixty miles-an-hour, and I wanted to drive at seventy miles, so I go to pass him, and he would speed up a little bit. But my car wouldn't go any faster than his car. It just bogged down. Then it started running like it only had two spark plug wires hooked up, jerking and shaking, and it just quit on me.

I went back to standard ignition, the standard distributor and all that, and it still ran, but it didn't run well. It was beautiful, in fact that New Yorker in 1976 was an Imperial, then they dropped the Imperial name and upgraded all the other cars. What was an Imperial, they made it a New Yorker, because I said I'm not the kind of guy that would drive an Imperial, but I am the kind of a guy that would drive a New Yorker.

Tannon Weber wrote:

My 1978 Chrysler Cordoba came with a Lean Burn-equipped 360/2bbl. At
the time I got it (December 2001, with 107,000 miles), the system
wasn't working very well, and didn't have any kind of sensor failure identification system that I could find. Given the lack of
performance options with the system as well as the general lack of
availability of parts and diagnostic equipment (I went to the oldest
Mopar dealer in town, which still has their Plymouth and Pentastar
signs up, and even they laughed at my suggestion of putting it on the
scope) I retrofitted to a standard carburetor system with conventional electronic ignition, splicing into the wiring harness,
replacing the distributor, and jury-rigging an electronic ignition module to the firewall. I saw about a five mile-per-gallon fuel
economy improvement with the change, and I still pass emissions tests.

A friend of mine has a 1978 Magnum with a 400/towing package setup
that also came Lean Burn-equipped. When the car was new he removed
the Lean Burn, fixed the wiring harness, and converted to standard.
In his estimation the conversion to a stock electronic ignition made
no appreciable difference in power compared to Lean Burn.

It would appear that when Lean Burn was new, if it worked properly
from the start it was fine. In my experience it ages quite poorly
though, and due to a combination of a lack of available replacement
parts and a lack of performance upgrades it's not worth trying to
maintain.

Keeping Lean Burn

Lean Burn can be made to work correctly, often with just a little work. It is usually good to try to fix it, before replacing it, because it does more good than harm when working.

Lean Burn diagnostics

Willis wrote,

After I bought my 1980 Newport, I added a set of Borg-Warner KoolWire II wires, (magnetic suppression, lower resistance). The car ran as expected for a 360 with a 318-size Carter BBD on it (the only year like that). As I got the carb idle system issues taken care of, it developed an intermittent "skip."

If I was sitting in a drive-thru at idle in gear, if the idle suddenly got a little rougher, but not much; as soon as I throttled into it to move, it'd start running very rough. One day, while idling, I noticed the idle get a little rougher. Just a little more quiver. But as soon as I eased forward, it really acted flaky. More throttle made it worse. The word "gutless" would have been too nice for the way it was running. I'd manually upshift it from 1-2 so that the rpm in 2 would not be too low.

I got it up to about 50 on the flat, in 2, but any small incline might have just as well be a full blown mountain. It was a struggle with massive amounts of throttle just to try to maintain 40mph on the overpasses. But I got it safely in the shop and then shut it off. I tried the restart and it immediately started and ran as if nothing was wrong . . . or had ever been wrong. Then it all fell in to place. Killing it and then restarting had reset the computer. I could have done that before coming to the shop!

In that short drive of about 15 miles, it managed to use about 1/2 tank of gas!

I looked in my service manuals for possibilities of what the problem might be. My Chrysler contacts recommended I check all of the wiring harness grounds, which I did, scraping paint and such for a better contact . . . no change.

I checked the spark plugs, for general principles. When I pulled the #1 spark plug boot off, the terminal stayed on the spark plug, yet the boot and wire were in my hand. It looked as if it hadn't been fully crimped from day one. I got some silicone spray and pushed more of the wire through the boot and reterminated the wire with the old terminal. Put everything back together and put it back on the spark plug. Nothing wrong with the way the plugs looked. I checked a few others and determined them to be good. Reterminating that wire solved the problem. I guess that as the engine shook a little at idle, sometimes if it shook just right, the connection would arc and send a back-feed to the distributor and computer and it'd go into Limp In mode.

I used to get amused at the many mechanics who would hold up the Lean Burn system as a "Gotta take it back to the dealer" complaint . . . until I found a Chilton book that told how to troubleshoot the system using a volt-ohm meter. The whole thing, like modern computer systems, is based on voltage change and resistance values. It's a more labor intensive process than simply hooking the Chrysler box to it, but it works anyway.

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In 1982 I bought my first car, a 1977 Chrysler Cordoba with a 400 In it and 70k miles. It was a dog from the get go. It ran okay but was no horsepower beast by far. Steep rear gears, 2.42, didnt help either. At 60 mph I averaged 15 mpg and 1700 rpm. At 70 mph, I could get 17 mpg at 2200 rpm. At 1700 rpm, the cam hadn't came in yet.
About a year or two later, it started running worse and would backfire so bad it sounded like a cannon going off just basically idling around town. My uncle that primarily drove and worked on Chryslers said, just eliminate the Lean Burn. So, I went and got a points distributor and installed it. It was the easiest way to convert it without cutting wires. It was at least tunable from there on out and ran better but still nothing spectacular.
Years later, my dad had a 1978 New Yorker with a 440. It was a dog too. Couldn't even power brake it on gravel. The Lean Burn died so I decided to swap it to electronic ignition. I had gained knowledge and skill to do it by then. Swapped in an electronic ignition box. Fairly easy if you know how to do it. I didn't have an old vacuum/mechanic advance distributor to swap in so I just used the Lean Burn distributor with zero advance. Set the timing to about 12* and went with it. WOW, what a difference! You could now power break this monster on asphalt and lay some serious rubber down! It also got 24 mpg on the highway! On a 440 no less! This was in 1990 when 4 cylinder cars were barely getting that on average. It may have even done better had I used an advance distributor.
 

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In 1982 I bought my first car, a 1977 Chrysler Cordoba with a 400 In it and 70k miles. It was a dog from the get go. It ran okay but was no horsepower beast by far. Steep rear gears, 2.42, didnt help either. At 60 mph I averaged 15 mpg and 1700 rpm. At 70 mph, I could get 17 mpg at 2200 rpm. At 1700 rpm, the cam hadn't came in yet.
About a year or two later, it started running worse and would backfire so bad it sounded like a cannon going off just basically idling around town. My uncle that primarily drove and worked on Chryslers said, just eliminate the Lean Burn. So, I went and got a points distributor and installed it. It was the easiest way to convert it without cutting wires. It was at least tunable from there on out and ran better but still nothing spectacular.
Years later, my dad had a 1978 New Yorker with a 440. It was a dog too. Couldn't even power brake it on gravel. The Lean Burn died so I decided to swap it to electronic ignition. I had gained knowledge and skill to do it by then. Swapped in an electronic ignition box. Fairly easy if you know how to do it. I didn't have an old vacuum/mechanic advance distributor to swap in so I just used the Lean Burn distributor with zero advance. Set the timing to about 12* and went with it. WOW, what a difference! You could now power break this monster on asphalt and lay some serious rubber down! It also got 24 mpg on the highway! On a 440 no less! This was in 1990 when 4 cylinder cars were barely getting that on average. It may have even done better had I used an advance distributor.
Hi! I think i have the same problem. I bought a Newport 78 last summer with a 400-4, and 45000 mi on it! All original. When it's cold it run great but after that i need to start very slowly from a stop or it will dye. I can't put the kickdown, it will pinging a lot! I changed the plugs, wires and nothing changed. I was thinking about changing all the vaccum hoses. I know a little about mechanic, can you explain to me what you did to byepass this Lean Burn? Thanks a lot
 

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I remember around 1978 a buddy of mine's dad had a 1977 Newport with a Lean Burn system. It began idling very rough and he asked me to look at it, tune it up. Problem turned out to be the Lean Burn computer electronics. I finally had to swap out the Lean Burn for a conventional Mopar electronic distributor, which solved the problem. Another buddy of ours had also bought a 1977 Cordoba with the 400-4 Lean Burn. While not a rocket by any means, it ran good, and as was mentioned, because of the very steep rear-end gearing it took a while, but would eventually get moving after it hit about 60. The concept was a good idea. The execution of it SUCKED, due to the infancy of using electronics underhood in an extreme heat/cold/vibration environment. Plus, even though Mopar had gone all electronic voltage regulators by then, most of them sucked as well. I can't tell you how many countless ones I replaced in all sorts of models from 1970 up until our 1984 Diplomat. It wasn't just bad internals in the regulators, but I must have scavenged dozens of the 2-prong electrical connectors with a short length of wiring that I often had to splice in to repair a defective connector. i used to look for them any trip to the junk yard, even if I was there for some other part. Always kept a stockpile on hand, just like any knowledgeable Mopar person knew to keep a spare ballast resistor in their glove box.:D
 

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Welcome to Allpar. I would advise against disabling, bypassing or removing the lean burn system. It is a 'system'; all the players need each-other in order to work as a team together. It allowed the cars to meet emissions without a catalyst and burn regular fuel.

Most of the time, the problem isn't even with the lean burn system. It is with the carburetor. A carburetor rebuild may help. Remember that your fuel system is 44 years old.
At 45K, there is no doubt that the car has sat. Sitting for long periods in improper storage conditions can sour fuel and rubber carburetor parts. Moisture can form acids which damage metals.

The early lean burn system was nothing more than a fancy way to control spark advance. It didn't control fuel until 1981.
The more precise spark advance control allowed for fuel calibrations toward leaner mixtures, sometimes too lean if the carburetor was compromised by wear, age or fuel quality.

There was a fuel quality issue. The refineries took back their octane level promise to the automakers after the fact. It was too late to change the fuel/advance calculations. Chrysler introduced a band-aid called the anti-ping valve. It was spliced into the vacuum hose to the computer. It took care of ping, but we still had sag & stumble issues.

Always diagnose first.
 

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The Chrysler Lean Burn engine control system: first onboard auto computer

The Lean Burn system was an early spark advance control system (introduced in 1976 and continuing to the 1980s) that was troublesome due to the nature of the contemporary electronic components, as well as the yards of vacuum hose and competent mechanics needed to keep it working. Materials technology eventually caught up, but many mechanics did not, and many owners simply switched to conventional carburetors.

View attachment 59821

Chrysler boasted, "Electronic Lean-Burn System, with its electronic spark control, is one of the most important developments in engine control since the 1920s and early 30s, when manual spark control was replaced by the automatic spark advance. Eight sensors and an electronic computer combine to adjust spark advance correctly for all driving conditions." (This turned out to be true in the long term; every car currently made uses electronic spark and fuel control.)

View attachment 59822

The second generation system, described below, came out a single year later, in 1977. It was similar but integrated electronic ignition and eliminated the centrifugal advance flyweights and one of the two pick-up coils from the distributor. In 1978 it was expanded to be used on most Chrysler V8s. By this time, Chrysler's related inventions - electronic ignition and the electronic voltage regulator - were already standard.

View attachment 59823

The 1978 description of the second generation notes, "This new computer consists of one integrated circuit board which computes all vital information for controlling the ignition system. It eliminates the starting pick-up coil and the centrifugal advance flyweights from the distributor and performs these functions electronically.
The spark-control computer also includes the electronic circuitry for the electronic ignition-thereby eliminating the separate control box for the electronic ignition."

View attachment 59824

Randy Miller wrote: Most people did away with Electronic Lean Burn, I think, because it was new technology and fear of "that electronic black box."

Back then, mechanics were being introduced to electronic devices never seen before in the automotive industry. I, on the other hand, was into electronics, and it fascinated me to know what was in that black box. I studied the system, learned how it worked, and eventually had local mechanics call me whenever a car came in with this system. Most of the problems turned out to be normal ignition or fuel problems, but, because it had "that black box," it must be the problem.

As years have gone by, I have found some problems with the computer itself. For example, I started my 1977 Chrysler Newport (with the original 400 Lean Burn engine) on morning and it was running fine and then for no reason it died. I started it again only to find it died a few second later. I traced the problem to the spark computer.

I took it apart, digging out the potting silicone to reveal the circuit boards. After some cleaning, I found a bad solder joint on one of the circuit boards. I got to thinking, what is the biggest problem with electronics in this application? Heat and vibration.

I retouched all solder joints, replaced the electrolytic capacitors, and repotted the boards back into the housing with potting silicone. The silicone was not cheap, but it put the unit back the way it was produced. After reinstalling it, the engine started and ran fine.

If Chrysler had mounted the unit on the body instead of the air cleaner as they did in production, I think a lot of these problems could have been resolved.

Chrysler broke the ground for the first computer controlled engine and I think they would not have had the problems they did back then if they would have taken a few extra steps. All car engines are now computer controlled thanks to their engineering team. Heat and vibration don't mix very well with electronics.

Yes, my old Chrysler still runs with the original ELB system!

Chrysler's Electronic Lean-Burn System, with its electronic spark control, was cited as providing:

  • Smooth engine warm-ups
  • Improved engine performance
  • Improved smoothness of engine operation
  • Controlled emissions-even before they reach the exhaust system
  • Less emission-control "hardware": several responsive sensors feed information to an electronic computer to keep the lean-burn engine performing efficiently.

The system measured:

  • 1. Engine speed (r.p.m.). As engine speed increases, spark plugs must be fired sooner for the engine power and efficiency needed. This sensor reads engine speed and signals the computer to adjust spark timing accordingly.
  • 2. Engine load. This sensor signals the computer to advance the spark for optimum fuel economy at part throttle.
  • 3. Throttle position. This electronic sensor reads accelerator pedal position and signals the computer to advance the spark under conditions when speed and load alone do not give the correct signal.
  • 4. Speed of throttle movement. This sensor signals the computer to advance the timing briefly in anticipation of the desired acceleration. The faster the acceleration, the longer the duration of extra advance. There is no lag.
  • 5. Air temperature entering the engine. As outside air enters the engine, its temperature is monitored by a sensor which signals the computer to advance the timing at cooler temperatures to enhance fuel economy and retard it at warmer ones to protect against destructive detonation or pre-ignition.
  • 6. Engine coolant temperature. This sensor tells the computer to limit spark advance during engine warm-up while the choke is on. This helps control emissions.
  • 7. Carburetor throttle open' or closed. This sensor operates a timing counter which remembers how long and how often the throttle is open or closed. It allows full spark advance at highway speeds but in city driving spark advance is modulated to control exhaust emissions.
  • 8. Engine starting. This sensor tells the computer when the engine has started and advances the timing for about one minute to cut down on engine stalls.

The electronic spark-control computer responds to data from all sensors and instantly adjusts the timing of sparkplug firings. Since conditions are constantly changing, the computer is constantly making instantaneous adjustments in spark-plug firings.

This second-generation spark-control computer consists of one integrated circuit board which computes all vital information for controlling the .ignition system. It eliminates the starting pick-up coil and the centrifugal advance flyweights from the distributor. Information for these functions is programmed into the spark-control computer and is performed electronically. The electronic circuitry for electronic ignition is also contained in the spark-control computer.

Examples of the system in operation:

1. The engine is cold. The coolant sensor tells the computer, which retards the spark so the engine isn't putting out a lot of pollution while the choke is on.
2. The engine coolant warms up. The sensor reports to the computer and the spark is advanced.
3. The engine is started in the morning and the car is driven away. Sensors tell the computer to provide spark advance to get you going.
4. Driving up a hill or pulling a trailer. The engine load sensor reads manifold vacuum and tells the computer whether the engine needs less spark advance to prevent detonation when pulling up the hill-or more spark advance going down the other side. Responsive spark timing does the job.
5. Driving on an interstate highway. The spark is advanced.
6. Rapidly depressing the accelerator. The sensor signals the computer to instantly advance the spark for more power to accelerate the car. There's no lag in spark advance like you get in ordinary engines.

The invention

The patent was granted in August 8, 1978, listing Gordon Fenn as the inventor. Marc Rozman told us that Gordon Fenn had come up with the system very quickly, and had also worked on substantial improvements to the 1980-81 Imperial electronic fuel injection system (after its introduction, to make it workable on vehicles in the field).

View attachment 59825

According to the patent, signals used to control spark timing included "a throttle advance signal, a programmed vacuum advance signal, a break-idle advance signal, an engine start advance signal, an engine speed advance signal and a fixed timing signal. These signals are algebraically summed together to develop a resultant spark timing signal representing desired spark timing. Individual signals are derived from transducer circuits which are responsive to various engine operating and/or ambient conditions."

The throttle advance included both throttle position and rate, increasing advance as the throttle opened; it was attenuated as the ambient air got hotter.

"The break-idle advance signal provides momentary advance when the engine throttle is displaced from the idle position. The engine start advance signal provides advance for a short interval after the engine has been started. The engine speed advance signal provides increasing advance as the engine speed increases. The fixed timing signal provides fixed timing which is used to adjust the basic timing for a given set of engine operating conditions. The control system is particularly advantageous when used in an engine which uses a leaner fuel-air mixture (17-18:1, for example) in comparison to presently used mixtures (15-16:1). Improvement accrues by way of reduction in exhaust emission products and better fuel economy."

An electronic feedback carburetor was used in 1979 on California cars with the one-barrel 225 and automatic. A digital microprocessor was included in 1980, replacing the analog system used in 1976-79. In 1980, a detonation suppressor system was also used on California V8 cars. The computer gained an adaptive memory system in 1982 for some four-cylinder cars.

Bill Wetherholt wrote:

Lean Burn was the start of the computer age. We had a 1977 Chrysler New Yorker, the first year for Lean Burn. It was a great car for the first year. But she was on the way to work one morning, and it just quit, the Lean Burn module had burned out. They replaced it with a rebuilt one, and the car never ran right after that. Once, I was trying to pass this guy in a Cadillac, he was going about sixty miles-an-hour, and I wanted to drive at seventy miles, so I go to pass him, and he would speed up a little bit. But my car wouldn't go any faster than his car. It just bogged down. Then it started running like it only had two spark plug wires hooked up, jerking and shaking, and it just quit on me.

I went back to standard ignition, the standard distributor and all that, and it still ran, but it didn't run well. It was beautiful, in fact that New Yorker in 1976 was an Imperial, then they dropped the Imperial name and upgraded all the other cars. What was an Imperial, they made it a New Yorker, because I said I'm not the kind of guy that would drive an Imperial, but I am the kind of a guy that would drive a New Yorker.

Tannon Weber wrote:

My 1978 Chrysler Cordoba came with a Lean Burn-equipped 360/2bbl. At
the time I got it (December 2001, with 107,000 miles), the system
wasn't working very well, and didn't have any kind of sensor failure identification system that I could find. Given the lack of
performance options with the system as well as the general lack of
availability of parts and diagnostic equipment (I went to the oldest
Mopar dealer in town, which still has their Plymouth and Pentastar
signs up, and even they laughed at my suggestion of putting it on the
scope) I retrofitted to a standard carburetor system with conventional electronic ignition, splicing into the wiring harness,
replacing the distributor, and jury-rigging an electronic ignition module to the firewall. I saw about a five mile-per-gallon fuel
economy improvement with the change, and I still pass emissions tests.

A friend of mine has a 1978 Magnum with a 400/towing package setup
that also came Lean Burn-equipped. When the car was new he removed
the Lean Burn, fixed the wiring harness, and converted to standard.
In his estimation the conversion to a stock electronic ignition made
no appreciable difference in power compared to Lean Burn.

It would appear that when Lean Burn was new, if it worked properly
from the start it was fine. In my experience it ages quite poorly
though, and due to a combination of a lack of available replacement
parts and a lack of performance upgrades it's not worth trying to
maintain.

(We've never heard anyone speak up for actually retaining Lean Burn.)

Lean Burn diagnostics

Willis wrote,




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Love this write up. I loved the 1981-1983 EFI Imperial despite the reported discrepancies. Had a co-worker who was a long time Chrysle rfan and bought one of the first Lean Burn 400 ci Cordobas. He was lucky enough to get a knowledgeable tech to maintain the car- nothing but accolades. I still dream of finding a 1981-1983 Imperial with the bugs worked out...
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