Observations on Chryser’s second generation Lean Burn system

[commando1]

And I can't count the ones I threw away. Including a NOS one in the factory packaging...

 

[1978 NYB]

I applaud those that attempt to decipher ELB and try to get it running.

I gave up years ago. Too easy to run my current MSD system that performs flawlessly.

Same with ATC II......

 

[Davea Lux]

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 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)

View attachment 340848

www.arizonaparts.com/MoparParts.aspx shows a few more compatible numbers. 4094022,4091072, 4106079. There were a bunch of revisions to the original part numbers.

Dave

 

[73 T&C]

www.arizonaparts.com/MoparParts.aspx shows a few more compatible numbers. 4094022,4091072, 4106079. There were a bunch of revisions to the original part numbers.

Dave

Thanks Dave....I knew you’d come through!

 

[73 T&C]

Here the collection I have that I needed to sort. One came in the trunk of the car when I bought it and one came with an air cleaner I wanted the lid from.

One of the good ones, besides the one in the car now, is not on the list. It is PN 4111441 and appears to be original. No foam underneath with reflective insulation like some of the rebuilt ones I’ve found. It also has all the pins in the socket.

The other one that works is PN 4111678. It has it’s foam insulation and all it’s pins as well.

The other two don’t work and are both missing the same pin which makes me think they are for another engine application entirely.

 

[Davea Lux]

Thanks Dave....I knew you’d come through!

Probably want to keep what you have as these things are starting to get scarce, most have been tossed at this late date because most of the folks familiar with these systems have retired and the test equipment is long gone.

Dave

 

[73 T&C]

Probably want to keep what you have as these things are starting to get scarce, most have been tossed at this late date because most of the folks familiar with these systems have retired and the test equipment is long gone.

Dave

That’s the plan. The museum will want all working examples when the time goes.

 

[73 T&C]

The two good ones! One goes into the stash and the other in the trunk along with a spare ballast resistor.

 

[Duncan]

I wonder if the ones with the pins missing were for the two barrel 318? I believe that's what I had on my 78 LeBaron 318.

 

[73 T&C]

Well it finally happened....

The spark control computer finally crapped out.

First it sputtered, then it cut in and out, then it died completely, then it started and died and started and died and started and..... BANG!!! Smoke out of the hood and scared myself to death. Thought I was on fire.

Right in the middle of a coast down to a light on US1 southbound in heavy afternoon traffic. It was running like a charm until then having just come off the end of I-95 (it ends) after about 20 mile return trip.

I must have looked like a B17 making a crash landing on fire. People just got out of the way!!!

Totally unrelated to today’s bit of drama.....

I had done a slight adjustment this morning on the choke to see if I could get a smoother transition from cold start to full temp. As soon as it hit 150 degrees, the enrichment would cut out she would run sort of rough. I thought a bit more choke would work and it did.

Luckily, I had my working spare computer in the trunk in a zip lock bag and just piggy backed it right in to get the rest of the way home.

Got a year and a half out of it to make it 43 years old. Not too bad... the spare is a Cardone aftermarket rebuilt unit that works fine. I added the sticker to make it look correct.

Time to get another spare

 

[commando1]

What can I say that hasn't been said.

 

[brougham brummel]

Question guys.Should an owner just ditch the lean burn or get a rebuilt computer.I may buy a car where the carb was changed and the lean burn deleted.Should i be worried about that?It,s a 78 New Yorker and can you get them to run correctly?thanks.B.B

 

[commando1]

Question guys.Should an owner just ditch the lean burn or get a rebuilt computer.I may buy a car where the carb was changed and the lean burn deleted.Should i be worried about that?It,s a 78 New Yorker and can you get them to run correctly?thanks.B.B

Yes! You can get them to run as smoothly as a Lexus.
Throw away ALL the Lean Burn and other pollution control crap, throw on the best street carb you can afford, have someone INTELLIGENT dial everything in properly. Not Carlos down behind the Taco restaurant.
And it will probably be cleaner out the exhaust pipe than in 1978.

 

[73 T&C]

Having a working Lean burn i can say that life with it ain’t easy while dialing it back in after an overhaul of the system. Short answer.... get a box.

To put your old lean burn into.

And swap in a direct connection or other aftermarket electronic ignition and new distributor with a vacuum advance. Even Carlos behind the Taco Bell or commando 1 can easily dial it in for you in about 10 min.

 

[brougham brummel]

.T.Ok.I will keep this in mind.Luckily i have an honest garage around the corner.I think i may have to wait longer on a car.Just the distance to go find a car out of state,time involved,energy to do so.By Friday i,m pooped.Glad to have you guys around.Thanks again.B.B

 

[commando1]

Even... commando 1 can easily dial it in for you in about 10 min.

Thanks, buddy....

 

[Fred A]

View attachment 198268

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.

Do you still have the leanburn on your car?