Observations on Chryser’s second generation Lean Burn system

73 T&C

Senior Member
FCBO Gold Member
Joined
Mar 19, 2013
Messages
2,048
Reaction score
3,128
Location
Coral Gables, Florida
9AA6A1F1-D5C2-4C14-8FFC-6FC7189E3F8A.jpeg


I know that most of you out there will give not a whit about any version of Chrysler’s Lean Burn Spark advance system.

In fact, most people regularly ditched the entire system fairly early on and converted their cars back to Chrysler’s earlier and indestructible electronic ignition system. And, not to be a hypocrite, I may end up doing the same..... eventually.

But, here goes... at least for posterity....

I bought my NYB with a failing spark advance computer in December of 2017. As I started sorting the car and the ignition, it became obvious that I would be tangling with the lean burn in one way or another.

I was forced, by my very stubborn habit of keeping my cars as original as practicable, to actually learn a bit about the system..... as much out of curiosity as anything.

Unlike the first generation Lean Burn System, the second version is actually much simpler. This later Lean Burn system eliminated both the second reluctor pickup (for the separate starting program in the computer) and the centrifugal advance in the much simplified distributor. Because it no longer ran a separate redundant ignition system just for starting the engine, the computer is also simpler. It has a single plug connecting it to:
Power
Ground
Throttle position transducer
Coolant temp sensor
Throttle idle switch
(Vacuum is measured on the module from a conventional vacuum pickup connected to a rheostat)

The carb is a specific version of the venerable Carter Thermoquad with a few unique changes made to have it produce a very lean mixture (16:1) and give the proper input to the spark advance computer.

These include:
  1. a vacuum operated enrichment circuit for the idle when cold that is governed by a thermal vacuum switch set to close at approx 150 degrees of engine temperature.
  2. Leaner main jets and needles
  3. Idle set screw placed on the right side to contact an idle switch and operate the throttle position and translation transducer
  4. Idle screws have a finer taper at the end for more precise tuning
Once I got it all set up correctly with properly working components together with the aid of the FSM, it actually runs fairly well with a few idiocincracies that are unique to it. These observed traits of the system are worth mentioning:

First... timing....

With no centrifugal or vacuum advance built into the distributor. Base timing is key to the operation of the system. The FSM and the decal on the yoke both call for basic timing to be set at 12degees BTDC. I’ve found that this car is a bit more responsive with about 4 additional degrees of advance. Any more yields pinging. I also run non ethanol premium 93 pump to eliminate this problem.

No vacuum leaks allowed!


With such a lean mix, any vacuum leak will yield exaggerated misfires and rough and unstable idle beyond what we’re used to on more convention earlier systems.

Carb must be very carefully balanced


Those fine idle mixture screws need to be tweeked just so to get as perfect a balance as possible to achieve a smooth idle..... regardless of how rich they are set. Also, richer is not at all better. Richer setting of the idle will force closing of the primary throttle to reduce rpm to spec. Transition from idle to power will therefore be more abrupt and could cause stall or backfire beyond poor responsiveness. I have set mine almost dead even (bit less for the left side) at 1-1/2 turns right now and am still tweeting it DOWN.

You need all 12 volts to make it run correctly...

This system does not like voltage drops much below 11v at any time. Battery, alternator and voltage regulator must we working correctly.

After all the above are done...How does it perform?

Car starts very eagerly with the first turn of the key, warm cold or hot.

Transition idle control and stability from cold to full operating temp is the biggest challenge. Standard choke and choke pull off need to be working correctly as well as carb balance.

Throttle response varies with temp of engine and how it’s driven. The ignition computer advances timing by 10 degrees at initial cold start for about 90 seconds and for about 60 seconds after warm restart to stabilize the temp and mix. Performance at these times is not different from the earlier non lean burn system. Like any cold engine with a carb, it’s a bit less powerful until it builds a little bit of temperature.

The timing advance is completely controlled by the computer. It is responsive to both throttle (transducer and idle switch) as well as load ( vacuum sensor) and, unlike a conventional vacuum/mechanical system, it can more quickly adjusts the advance and retarding of ignition timing.

However, emissions control was also its reason for being and, as such, it has some mid throttle quirks that are not what we’re used to.

The electronic spark advance will not snap the advance of timing back up like a vacuum advance will. Instead it builds it up to its max advance over time (5 degrees at a time) after the throttle is off the idle stop. Once built up, the advance will remain in memory for up to 5 seconds after closing the throttle idle position switch. After that, it will start reducing the advance in memory by the same steps until you get back to basic running timing.

If, for example, you coast to allow the engine braking to slow you down. You will activate the idle switch which will return the advance back to basic timing if you coast long enough. Depending how long you leave the throttle on idle will affect your initial advance upon re-opening the throttle. This can be felt as a momentary lack of power/response at part throttle... it’s not a stumble like a misfire. Just a reduced power level as the computer rebuilds the advance.

This can be a bit irritating but it’s not “wrong”. These ain’t no road runners were talking about. So, although slightly noticeable, the momentary delay in full available power at part throttle is not a deal killer. Should you need it, you can increase throttle to make up the difference or you can give it a little stab which helps bump up the advance based on the transducer signal.

In normal operation, it is really no big deal and, to most people... probably not even noticeable.

Like previous Thermoquad equipped 440’s a push past the primaries will yield both full power and that glorious sound whenever you want or need it. Hit it at the right rpm and speed and you get a nice kickdown and nudge in the rear. (You want a kick in the rear.... get a hemi)

Adjusting the transmission kickdown to get the trans to hold in gear a bit longer also helps both performance of the overall package and allows for a little more revs you may want to have at the ready should you need to mash it good.

I set mine so it shifts to 2nd at 10-12moh and into 3rd at 25 mpg..... taking it old lady easy. A bit more aggressive driving takes the above to 28/29 for second and as much as 60 for third. When I got it, this car was shifting to second in as early as 5mph and third at 15mph. It was crap.

Finally, it took me several months to sort out the car and well over two months to get the lean burn to work as it should. I can see where people could get frustrated very easily as this system is pretty finely tuned. It will not react well to what are minor issues on the previous system of just electronic egnition. I can also see where it can become the focus of symptoms of some other system weakness..... such as weak or faulty wires, plugs and coil as well as an out of tune carb.

Like everything else, KISS is the buzz word for it and don’t think it is the first culprit.
 
Last edited:

mr. fix it

Old Man with a Hat
Joined
Aug 14, 2013
Messages
7,767
Reaction score
8,192
Location
Canada
The Lean Burn runners here thank you for your tenacity and recounting of what you did!:thumbsup:
 

mrfury68

Senior Member
Joined
Jul 15, 2015
Messages
1,451
Reaction score
1,736
Location
Bethel Park PA
Great job by you! Quite a bit of attention to detail, which is required to work on these systems. I'm sure all the guys who have Lean Burn equipped cars are grateful for this post.
 

Pclancy

Active Member
Joined
Mar 27, 2016
Messages
230
Reaction score
129
Location
Washington, DC
Even tho I ditched my lean burn at the first sign of problems, posts like this are why Javier is almost peerless among FCBO members.
 

saforwardlook

Old Man with a Hat
FCBO Gold Member
Joined
Oct 8, 2011
Messages
7,254
Reaction score
12,232
Location
California
I gave Javier credit for correctly describing what the spark control computer was doing - it was simply doing what mechanical/vacuum type valves used in previous years and other gimmicks like OSAC valves (orifice spark advance control valves) and EGR (exhaust gas recirculation valve) timers did, but did them electronically instead.

But while I am probably one of the most staunch proponents of "original" on this site, I would also be the first person to ditch anything to do with "lean burn". It was one of the most retarded (literally and theoretically) programs Chrysler ever came up with. Actually, it was the brainchild of an engineer named Gorden Fenn, who was an ivory towered intellectual type that seemed to know little, if anything, about production tolerances of carburetors that could be achieved in the real world. While theoretically, the idea had merit, the electronics to make something like that work were not available until fuel injection came about approximately 10 years later along with oxygen sensors to control fuel delivery more precisely. And even then, the whole "lean burn" idea was flawed from the beginning.

Chrysler didn't even know how to utilize the catalytic converters that went into production until after 1979, while GM, which helped develop the catalytic converters knew fully and correctly how to utilize them to lower emissions out the gate in 1975. Chrysler thought it would be really smart and utilize lean burn to pass emission standards and get good fuel economy and eliminate the catalytic converters. What a joke that was!

Chrysler ended up producing cars with terrible driveability, poor fuel economy and miserable performance and still ended up using catalytic converters because their lean burn systems were so variable in delivering what was needed for uniform driveability and emissions as a result of inadequate fuel management with a mechanical device (carburetor). And then in California in 1977, the California Air Resources made Chrysler recall every 318 produced for the state because in the agency's own testing for emissions compliance of a sample of vehicles, they couldn't even complete the cold start phase of the dynamometer emission test without multiple passouts that invalidated most of the tests - and they ruled the cars a driveabilty hazard! Good work Chrysler!

Unfortunately, there was no magic bullet to fix those cars and so they ended up taking out more performance and run leaner when warmed up but made the cold start just slightly richer to improve driveability. And while they didn't pass out as much around the 70F cold start test, they still passed out plenty when temperatures got lower at cold start.

GM, on the other hand, went the other way right out of the gate in 1975, running rich fuel/air mixtures off idle and balanced mixtures under cruise conditions to keep good performance and driveability - and they ran plenty of spark advance, but got low nitrogen oxide emissions by running relatively high amounts of exhaust gas recirculation to lower nitrogen oxide emissions instead of retarded spark and lean fuel/air mixtures like Chrysler did (along with exhaust gas recirculation too). So GM cars drove brilliantly (the relatively rich mixtures and healthy spark advance completely covered up the relatively small amounts of exhaust gas recirculation used to lower nitrogen oxides while the Chrysler products were miserable in every respect. So GM cars' catalysts covered up the increased hydrocarbons and carbon monoxide generated with those converters and got low nitrogen oxide emissions with exhaust gas recirculation and drove great.

Chrysler ended up generating high hydrocarbon and carbon monoxide emissions due to stumbles, pass outs/restarts, needing to dip hard into the accelerator pedal to get decent performance which did generate richer mixtures and so on, plus almost no spark advance under most city driving conditions, and high hydrocarbon, nitrogen oxide emissions and lousy driveability even with a catalytic converter.

There is no doubt in my mind that lean burn paved the way to Chrysler going bankrupt in 1980 because their cars were miserable to drive compared to those from GM and gave customers nothing but frustrating experiences. That and a rush to chintziness near the end when the balance sheets were blaring sirens and red warning lights that doom was on the horizon.

I wouldn't hesitate to every pull off all the lean burn crap on Chrysler products in the 1975 - 1979 era and put on associated parts calibrated like GM cars instead. Lean Burn was absolute garbage and there was nothing worth saving about any of it.
 

Duncan

Well-Known Member
Joined
Nov 24, 2014
Messages
547
Reaction score
446
Location
Woodland CA
I now fully appreciate what genius' my brother and father-in-laws were. My b-i-l was a computer repairman at a local airforce base and my f-i-l was a fantastic shade tree mechanic, having worked on everything from his first Model T to his current (at the time) Crown Vic. Our 78 LeBaron had the LeanBurn system and was giving us nothing but trouble - hard starting, fouled plugs, rough running, no power,, etc. I found a pamphlet at our local Kraegens about the leanburn system and took it home. Next time they were visiting I showed it to them. They went out to the car, took that information and made that car run like a dream. My b-i-l figured out how to run some kind of test on the LB computer to figure out if it was working properly and found out it wasn't. He found it was failing at a certain point and told me what to tell the service department to get the same results to prove the computer needed replacing. It worked and it was replace under warranty (But not until after I had to explain to the service department twice what to do). My bil and fil then got under the hood and adjusted the carb, fixed the choke and did a few other things that I don't remember. The result was that the car ran like a top from then on. Smooth and strong and got 25 mpg on the highway with the AC going. I regret having traded that car in to this day - and all because of my smart in-laws nearly 40 years ago.
 

saforwardlook

Old Man with a Hat
FCBO Gold Member
Joined
Oct 8, 2011
Messages
7,254
Reaction score
12,232
Location
California
I now fully appreciate what genius' my brother and father-in-laws were. My b-i-l was a computer repairman at a local airforce base and my f-i-l was a fantastic shade tree mechanic, having worked on everything from his first Model T to his current (at the time) Crown Vic. Our 78 LeBaron had the LeanBurn system and was giving us nothing but trouble - hard starting, fouled plugs, rough running, no power,, etc. I found a pamphlet at our local Kraegens about the leanburn system and took it home. Next time they were visiting I showed it to them. They went out to the car, took that information and made that car run like a dream. My b-i-l figured out how to run some kind of test on the LB computer to figure out if it was working properly and found out it wasn't. He found it was failing at a certain point and told me what to tell the service department to get the same results to prove the computer needed replacing. It worked and it was replace under warranty (But not until after I had to explain to the service department twice what to do). My bil and fil then got under the hood and adjusted the carb, fixed the choke and did a few other things that I don't remember. The result was that the car ran like a top from then on. Smooth and strong and got 25 mpg on the highway with the AC going. I regret having traded that car in to this day - and all because of my smart in-laws nearly 40 years ago.

If your Le Baron was a 318 sold initially in California, it would have had a 4bbl carburetor on it that should have run pretty well, because both it and the 360-4 bbl were calibrated on the rich side, not lean starting in 1978 for California 318s and California and Federal 360-4 bbl packages. Even though they still had the spark control computer, they didn't have all the junk calibrated into it that the earlier Federal (49 state cars) did that really were lean burn. You could not buy a new 318-2bbl carburetor equipped vehicle in California in 1978 or 1979 because they woudn't pass emissions nor would they run worth a crap. Those two packages were the first ones to utilize most of the stuff that GM already knew years before and both utilized well-calibrated richer Thermoquads. The 318-4bbl could have been even better than it was relative to performance off the line, but Chrysler managment wouldn't spend the money for an intake manifold with smaller intake ports sized for a 318 to ensure good low speed air flow (throttle velocities) and so they utilized the large intakes used on the 360-4 models out of necessity. But those 318-4s ran smoothly without passouts and had adequate performance off the line, but wasn't as good as it could have been in that respect, but ran well otherwise (when everything was right as yours finally was).
 
Last edited:

73 T&C

Senior Member
FCBO Gold Member
Joined
Mar 19, 2013
Messages
2,048
Reaction score
3,128
Location
Coral Gables, Florida
There comes a time when if you believe your own bullshit your likely to take it too far.

In ‘73, Chrysler made a big deal of their participation in the Apollo program pitching their cars next to the command module with pilot and pitchman Arthur Godfrey. “Extra Care in Engineering”. and all... it made a difference but not one they expected or were prepared for.

I think they thought they could pull it off when they expanded their excellent electronic ignition with a spark advance computer in the lean burn system. The logic of the decision was most likely that on achieving the dual goal of getting a few more years out of their aging stock of block designs and; not going to the more expensive catalytic converters until later.

Had it all worked as planned it would have been a true coupe for Chrysler to the market.

I can certainly attest to the variability of (even the same) carb as a major factor in the drivability issues. In fact I just redid mine due to a fault in the phenolic bowl.

Having said that, I agree it’s not the best but it was what they had at the time. Without an analyser, I was able to get my Lean Burn system back up and running passably well. It took some stubbornness on my part and a whole lot of reading here and elsewhere. I also admit I defeated the original system somewhat by going to some richer main jet metering rods in the Thermoquad..... to make it a little more enjoyable to drive by boosting the performance a bit.

But otherwise it runs as designed .....and passably well.
 
Last edited:

Duncan

Well-Known Member
Joined
Nov 24, 2014
Messages
547
Reaction score
446
Location
Woodland CA
If your Le Baron was a 318 sold initially in California, it would have had a 4bbl carburetor on it that should have run pretty well, because both it and the 360-4 bbl were calibrated on the rich side, not lean starting in 1978 for California 318s and California and Federal 360-4 bbl packages. Even though they still had the spark control computer, they didn't have all the junk calibrated into it that the earlier Federal (49 state cars) did that really were lean burn. You could not buy a new 318-2bbl carburetor equipped vehicle in California in 1978 or 1979 because they woudn't pass emissions nor would they run worth a crap. Those two packages were the first ones to utilize most of the stuff that GM already knew years before and both utilized well-calibrated richer Thermoquads. The 318-4bbl could have been even better than it was relative to performance off the line, but Chrysler managment wouldn't spend the money for an intake manifold with smaller intake ports sized for a 318 to ensure good low speed air flow (throttle velocities) and so they utilized the large intakes used on the 360-4 models out of necessity. But those 318-4s ran smoothly without passouts and had adequate performance off the line, but wasn't as good as it could have been in that respect, but ran well otherwise (when everything was right as yours finally was).

If my memory serves me right I believe you are correct on the 4 bbl carb. I don't know if it was done deliberately to get the rich calibration but the main problem with the whole system-on my particular car anyway, was that the choke was set so heavy it never fully opened and was so rich it I think it was even dumping raw gas out of the tailpipe. To set the choke was really a hick setup. It had a round spring set in a square box on the manifold that was then attached to a rod that attached to the choke. I don't remember all the details or the parts involved but I do remember - and this was according to the manual - to set the choke you had to either straighten or bend the rod whatever distance was necessary to make the needed adjustment. But we found the choke was so heavy there wasn't enough length/space on the rod to make the adjustment. We literally took the spring out of the square box on the manifold and turned it a whole quarter turn and then put it 'back' in the box. That left hardly any choke on the carb at all but it was enough. Like I said earlier, along with whatever else my in-laws did, that car ran like a dream from then on. I wish I still owned it.
 

saforwardlook

Old Man with a Hat
FCBO Gold Member
Joined
Oct 8, 2011
Messages
7,254
Reaction score
12,232
Location
California
If my memory serves me right I believe you are correct on the 4 bbl carb. I don't know if it was done deliberately to get the rich calibration but the main problem with the whole system-on my particular car anyway, was that the choke was set so heavy it never fully opened and was so rich it I think it was even dumping raw gas out of the tailpipe. To set the choke was really a hick setup. It had a round spring set in a square box on the manifold that was then attached to a rod that attached to the choke. I don't remember all the details or the parts involved but I do remember - and this was according to the manual - to set the choke you had to either straighten or bend the rod whatever distance was necessary to make the needed adjustment. But we found the choke was so heavy there wasn't enough length/space on the rod to make the adjustment. We literally took the spring out of the square box on the manifold and turned it a whole quarter turn and then put it 'back' in the box. That left hardly any choke on the carb at all but it was enough. Like I said earlier, along with whatever else my in-laws did, that car ran like a dream from then on. I wish I still owned it.


My mother also decided she wanted a 1978 Le Baron 2 door Medallion model when it came out. She got the 318-4 bbl engine option that I recommended as well and she loved that car. It had every option available and she really enjoyed driving it - right size, really comfortable and ran like a top with its non- lean burn 4 bbl. It also got great gas mileage. Sadly, she passed away 2 years later after undergoing treatment for breast cancer. I had a hard time looking at the car after that and sold it, but now I wish I still had it. It was like new when it left and it was one of my favorite cars. It looked identical to the one below:

lebaron2-e1463173831606.jpg
 

73 T&C

Senior Member
FCBO Gold Member
Joined
Mar 19, 2013
Messages
2,048
Reaction score
3,128
Location
Coral Gables, Florida
Under the heading of don’t blame the Lean Burn I advised above, I was able to trace a rougher (than I’d like) idle during transition to operating temp to a very minor leak in the TQ’s fuel bowl.

You can see this on my other thread.

This minor repair and a check of the ignition wires (number 8 wire was bad) and plugs (cleaned, regapped and reinstalled) have delivered a very smooth transition to operating temp today......and a very acceptable smooth idle at stop lights with car in gear.

Up until now it would come to a stop with a smooth idle and slowly degrade to a bit rougher idle.

I suspect a leaking lifter and upped the viscosity a bit with some STP oil treatment for the zinc if nothing else.

Need to put a gauge on the oil pressure to make sure warm idle pressure is good. No light coming on though.

One interesting observation on the lean burn is how it step advances slowly under constant light throttle. You can actually feel the increase in power as it works to increase timing.... forcing you to lay off the throttle as you approach your desired speed quicker.... like when entering a highway from an on-ramp.

One more thing, given that the idle screws on the carb for the lean burn have both a finer point and thread, I turned out both sides 1/2 turn to two full turns to richen the idle a bit to compensate for the torque converter load a bit.
 

angus66

Member
Joined
Feb 7, 2014
Messages
78
Reaction score
126
Although the lean burn on my '77 Newport was disabled when I came to own the car, I like the idea of it. And I think given the time I would have liked to have recommissioned it. Given three kids, two other collector cars, maintaining two dailies, a full-time job and a wife who would view being caught stranded a shooting offense - Holley Sniper EFI was my answer - And I am happy to report, at the near the end of the second driving season, the setup is working great - no issues. That said, being a software developer by trade I'd like to see someone do something interesting with the original Lean Burn Computer housing and a microcomputer - like a Raspberry PI. It would be nice to be able to dial in a lean-burn computer via a laptop.
 

Davea Lux

Old Man with a Hat
FCBO Gold Member
Joined
Mar 27, 2017
Messages
9,016
Reaction score
8,237
Location
Cornelius Or
I gave Javier credit for correctly describing what the spark control computer was doing - it was simply doing what mechanical/vacuum type valves used in previous years and other gimmicks like OSAC valves (orifice spark advance control valves) and EGR (exhaust gas recirculation valve) timers did, but did them electronically instead.

But while I am probably one of the most staunch proponents of "original" on this site, I would also be the first person to ditch anything to do with "lean burn". It was one of the most retarded (literally and theoretically) programs Chrysler ever came up with. Actually, it was the brainchild of an engineer named Gorden Fenn, who was an ivory towered intellectual type that seemed to know little, if anything, about production tolerances of carburetors that could be achieved in the real world. While theoretically, the idea had merit, the electronics to make something like that work were not available until fuel injection came about approximately 10 years later along with oxygen sensors to control fuel delivery more precisely. And even then, the whole "lean burn" idea was flawed from the beginning.

Chrysler didn't even know how to utilize the catalytic converters that went into production until after 1979, while GM, which helped develop the catalytic converters knew fully and correctly how to utilize them to lower emissions out the gate in 1975. Chrysler thought it would be really smart and utilize lean burn to pass emission standards and get good fuel economy and eliminate the catalytic converters. What a joke that was!

Chrysler ended up producing cars with terrible driveability, poor fuel economy and miserable performance and still ended up using catalytic converters because their lean burn systems were so variable in delivering what was needed for uniform driveability and emissions as a result of inadequate fuel management with a mechanical device (carburetor). And then in California in 1977, the California Air Resources made Chrysler recall every 318 produced for the state because in the agency's own testing for emissions compliance of a sample of vehicles, they couldn't even complete the cold start phase of the dynamometer emission test without multiple passouts that invalidated most of the tests - and they ruled the cars a driveabilty hazard! Good work Chrysler!

Unfortunately, there was no magic bullet to fix those cars and so they ended up taking out more performance and run leaner when warmed up but made the cold start just slightly richer to improve driveability. And while they didn't pass out as much around the 70F cold start test, they still passed out plenty when temperatures got lower at cold start.

GM, on the other hand, went the other way right out of the gate in 1975, running rich fuel/air mixtures off idle and balanced mixtures under cruise conditions to keep good performance and driveability - and they ran plenty of spark advance, but got low nitrogen oxide emissions by running relatively high amounts of exhaust gas recirculation to lower nitrogen oxide emissions instead of retarded spark and lean fuel/air mixtures like Chrysler did (along with exhaust gas recirculation too). So GM cars drove brilliantly (the relatively rich mixtures and healthy spark advance completely covered up the relatively small amounts of exhaust gas recirculation used to lower nitrogen oxides while the Chrysler products were miserable in every respect. So GM cars' catalysts covered up the increased hydrocarbons and carbon monoxide generated with those converters and got low nitrogen oxide emissions with exhaust gas recirculation and drove great.

Chrysler ended up generating high hydrocarbon and carbon monoxide emissions due to stumbles, pass outs/restarts, needing to dip hard into the accelerator pedal to get decent performance which did generate richer mixtures and so on, plus almost no spark advance under most city driving conditions, and high hydrocarbon, nitrogen oxide emissions and lousy driveability even with a catalytic converter.

There is no doubt in my mind that lean burn paved the way to Chrysler going bankrupt in 1980 because their cars were miserable to drive compared to those from GM and gave customers nothing but frustrating experiences. That and a rush to chintziness near the end when the balance sheets were blaring sirens and red warning lights that doom was on the horizon.

I wouldn't hesitate to every pull off all the lean burn crap on Chrysler products in the 1975 - 1979 era and put on associated parts calibrated like GM cars instead. Lean Burn was absolute garbage and there was nothing worth saving about any of it.

These systems as noted, were legend for lousy driveability and these systems were uniformly hated by Chrysler techs of the era, my self included. We had a constant parade of these vehicles that would not pass emissions, you could put the darn things on the test equipment and have them dialed in to pass and by the time the owner got the car to DEQ a few days later the car would flunk again. Some of that was because as noted the system functioned poorly with an EGR valve because the two devices were not well calibrated to work together. Another constant problem was the mounting location of the computer on the air cleaner. In hot climates or stop and go traffic conditions, the electronics would over heat and fry themselves. Vibration was another constant problem because the rushing air thru the air cleaner at full throttle shook the circuit board and fractured the circuit pathways. I bough a brand new '77 Sport Fury with the 400 lean burn and went thru 3 computer's in the year that I owned the car, twice in the middle of the desert, stone cold dead. It was very obvious that even the factory reps teaching techs about the Lean Burn system were clueless as to why the systems were suffering repeated failures. For a time they had us installing condensers on the electronics because the failures were believed to be static related. Did not help a bit. Then they tried to tell us the systems were failing DEQ because we were not setting the carbs to factory specs. Wrong, most of the time the cars would not pass at factory specs. The systems lacked any type of compensating ability for changes in humidity, altitude and fuel octane ratings all of which contributed to driveability problems. A small vacuum leak pretty much any place also effected these systems very adversely. ATC-2 ring a bell? You could get these Lean Burn cars to run right, but not in a range where there was any chance of them passing an emissions test. In short, I agree with saforwardlook, the Lean Burn is not worth keeping.

Dave
 

73 T&C

Senior Member
FCBO Gold Member
Joined
Mar 19, 2013
Messages
2,048
Reaction score
3,128
Location
Coral Gables, Florida
@Davea Lux,

I’m pretty sure mine wouldn’t pass emissions testing either; not with the current bigger metering rods and richer idle. Luckily, I don’t have to worry about that with my car due to aging out and living in Florida.

But a ‘78 test required very little to pass at the time... as I recall. With the cat, usually leaning out the idle circuit to just above stumble and making sure it was warmed up usually did the trick.

I should put it on a tester and see how much warmer I’m making the planet some day.

I just wanted it to work and figure it out like a big puzzle. As I said, it took a while for me to get it to an acceptable level of performance ... and I can easily see it not being up to production standards.

No doubt that the poor techs took the brunt of the complaints and were stuck with trying to do the final production work outs in the field. My own 440 has the replacement TQ that was a warranty replacement at the time. Also, the testing and calibration equipment provided (and available) at the time were of only limited help. As I said previously, it was a big jump to make in technology for the time.

Now that I got it running. I may just retire it to the trunk as a working system. I’ve also got a working spare computer in a sealed bag in the trunk until I do because...hey, I’m stubborn (and possibly a little crazy) but not stupid.

I equally love my Thermoquad and my working ATC II in this car.

I also drive a Citroën SM which really IS crazy.
 
Last edited:

owen martin

Member
Joined
Oct 14, 2015
Messages
73
Reaction score
20
Location
Bon Accord Alberta
Well you guys are a wealth of history and tech smarts on these old cars and Chrysler’s Faw Paw’s, I really enjoyed ya all’s take on those damn lean burn years! Do any of you guys have any smarts and ideas on how to successfully get my 67 Monaco 500 383V8 2 barrel AC up and running permanently without leaks that I cannot seem to detect or can the experts!? Naturally it was changed from R12 to 134A years ago but I have a feeling the molecule of the 134A is smaller than the R12 and leaks past the seals and maybe even the hoses? Any ideas would help as Ive got the same problem with my 71 Mark 111 Lincoln too!?
 

Davea Lux

Old Man with a Hat
FCBO Gold Member
Joined
Mar 27, 2017
Messages
9,016
Reaction score
8,237
Location
Cornelius Or
Well you guys are a wealth of history and tech smarts on these old cars and Chrysler’s Faw Paw’s, I really enjoyed ya all’s take on those damn lean burn years! Do any of you guys have any smarts and ideas on how to successfully get my 67 Monaco 500 383V8 2 barrel AC up and running permanently without leaks that I cannot seem to detect or can the experts!? Naturally it was changed from R12 to 134A years ago but I have a feeling the molecule of the 134A is smaller than the R12 and leaks past the seals and maybe even the hoses? Any ideas would help as Ive got the same problem with my 71 Mark 111 Lincoln too!?

If the systems are currently discharged, start by checking to see if the system o-rings have been replaced with the modern green ones, they are a high density material that is designed for R-134a. The second likely source of a leak is the shaft seal on the compressor, compressor seals us a combination of gas pressure and refrigerant oil to create the seal. Usually if the front seal is leaking, there will be oil around the clutch hub. If this is the source of the leak, the shaft seal will have to be replaced. The other place there is likely to be a leak is at the fittings for the low side line, these fittings have a barbed shank that pierces the inner membrane of the suction hose and this will sometimes cause a leak. The usual solution is to have a new suction hose fabricated.

R-134a is indeed a smaller and lighter gas molecule that is more prone to leaking out of systems that were not designed for it. These best permanent solution to leakage would be to go to a modern Sanden compressor with all new hoses. There is a kit to mount this compressor for most applications. The other option is to check the system on regular basis for state of charge and keep it topped off. If it took years for your system to leak down, you probably do not have a large leak. RV-2 compressors have a high failure rate running R-134a because if the system is not kept fully charged, the oil in the system tends to leave the compressor and pool in the condenser, filter dryer and evaporator. This starves the compressor for lubricant and a burn out of the compressor results.

If you search this site, there are numerous threads on the Sanden conversion and leakage issues with R-134a.

Dave
 
Last edited:

73 T&C

Senior Member
FCBO Gold Member
Joined
Mar 19, 2013
Messages
2,048
Reaction score
3,128
Location
Coral Gables, Florida
Lean Burn day today.

Don’t get me wrong.... it running fine these days. It was just that I’ve built a collection of computers beyond the ones I found in the trunk and needed to sort them.

I’m pretty good at internet research but haven’t been able to find a complete list of the compatible computers and original part numbers for my 78. I was able to make one by looking at the aftermarket ones that are still available. Therefore, for posterity, here it is.

original part numbers I’ve been able to find for a 78 440 four BBL Chrysler/Plymouth/Dodge are:

4091791, 4091923, 4106073

I got the above from the compatibility description for the Blue Streak Manufacturing (which also goes by the name of Electromotive) with the PN of ECC153M which is specifically and only compatible with the year engine combo above.

00FAEC22-EC55-4893-A766-6820193CC32D.jpeg


same manufacturer also shows a compatible unit under PN: ECC112M the following OEM part numbers that will also work:

4091730, 4091731, 4091787, 4106061, 4106067, 4106070, 4106103, 4111253, 5206061

However, these are also compatible with the same year 318. Both are called out as VIN “T” for the 440 four barrels.

Does anyone know where there might be a list of PN’s by year and engine application similar to the great lists there are for Thermoquad’s?
 
Last edited:
Top