Mechanics

NO SPARK...NO ICM

1988 Chrysler 5th Avenue • V8 2WD Automatic •

Helping a family try to get a 1988 Chrysler Fifth Avenue to run. There is no spark. We replaced plug wires, rotor, distributor cap and ignition coil. The parts store sold us an Ignition Control Module, but we cannot find one to replace under the hood, firewall, fender wells, anywhere. Does it really have one? What else could it be? Distributor pick up coils?
Thanks for the help.
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Frozen Rebel
April 19, 2011.



That does not use the terribly reliable four or five pin ignition module. On the cars that do, that module must be grounded by bolting it to the body. You should see the Engine Management Computer bolted to the air cleaner housing.

First of all, unplug the two-wire connector from the distributor and measure the resistance of the pickup coil. There could be two of them. If there is, measure them both but don't mix them up. As I recall, you should find around 500 - 700 ohms. The exact value isn't critical. You just want to be sure there is not an open circuit. That can occur from the pickup plate turning and flexing the tiny wires on the pickup coils.

As an alternative test, IF there are indeed two two-wire connectors, switch them around to see if the engine starts. If it does, it will stall as soon as you let go of the ignition switch. Then you will know one of the coils is open. When two of them are used, one is for cranking and one is for running. They just change the timing a little to make it easier to start. There will also be a relay that switches between them.

Let me know what you find. I really think they should sell that car. That was my ultimate dream car many years ago. I'd still like to find a nice red one!


Caradiodoc
Apr 19, 2011.
Sell the car because you would like to buy it? Or, because there are more problems on the horizon? This family cannot afford repeat maintenance bills.
I will check the pick up coils tonight after work. Thank you very much for the tip.


Tiny
Frozen Rebel
Apr 19, 2011.
Yup. That's tongue-in-cheek but I would still like to own one. Had a chance to buy one many years ago. Feller brought it in for an oil change and to get some minor dings fixed before he put it up for sale. The only way I could tell the engine was started and running was the oil light went off. I very much prefer these cars to the over-complicated nightmares the engineers are pushing on us now. My daily driver is an '88 Grand Caravan that I refuse to get rid of.

Anyhow, verify you have the computer on the air cleaner housing, then check the resistance of the pickup coil(s), then holler back. Also check for 12 volts on the blue wire to the ignition coil when the ignition switch is in the "run" position.


Caradiodoc
Apr 19, 2011.
I think your advice to sell might be right. There is one pickup coil on the distributor measuring 270 ohms. It looks good. The odd thing is that both sides of the ignition coil are measuring about 11.1 volts with the switch on. If I am not mistaken, I think the negative side should be to ground. I now suspect the culprit is the component seen in the attached photo. My internet search indicates this may the once innovative, but now defunct, "Lean Burn" system. There is a reference to a Mopar conversion kit, but neither NAPA or O'Reilly's has a cross reference. My question now is: Is the old car worth any more effort and cost to resurrect the spark of life? I know with Easter coming, there is always hope.


Tiny
Frozen Rebel
Apr 20, 2011.
Chrysler has more "firsts" under their belt than any other manufacturer and the Engine Computer is one of those. They were first with the alternator, (they copyrighted the term), in 1960, first with a trouble-free electronic voltage regulator in 1970, first with anti-lock brakes in 1969, first with electronic ignition instead of the miserable breaker points in 1972, first with the electronically controlled carburetor that got a very peppy 54 mpg in the Horizon Miser in the early '80s, first with a lockup torque converter for better fuel mileage in 1977, first with a computer-controlled transmission in 1989, first with air bags in 1987. I could go on but you get the idea. They were also the first in 1976 with a computer to calculate spark timing based on numerous variables. Before that we could only adjust timing based on engine speed and load. That first computer was indeed the "Lean Burn" system. It was called that because it could make the engine run well on a 17: 1 air / fuel mixture instead of the normal 15.7: 1. Running too lean normally results in hesitation and sputtering, but running a little too rich wasn't noticed so all cars ran too rich most of the time. Carburetors can only be adjusted to provide the proper mixture at idle and highway speed. Anything in between had to be too rich enough to insure it never fell below the perfect 15.7: 1.

That computer is exactly the same as was used in the front-wheel-drive cars except it was mounted on the side of the inner fender. In both cases intake air is run through it to cool the high-current coil switching transistor. Long before 1988 Chrysler had their computers perfected so they hardly ever had a problem. I worked for a very nice family-owned Dodge dealership from 1989 through 1999. I never replaced a single Engine Computer until they came out with the redesigned Caravan disaster in 1996.

While it's possible your computer is defective, that would be very surprising. It's the last thing I would suspect. Many years ago I had, (still have) a 1978 model with that system and I noticed it wasn't creating any timing advance. That severely hurt the fuel mileage. At that time I didn't understand how to troubleshoot the system, but now I know that was caused by a sensor that I didn't understand. Instead, I dropped in a distributor from an older engine that had the vacuum and mechanical advance built in. In another misguided attempt at a repair gone wrong, I wired in the five-pin ignition module that you can still buy for 25 bucks. That engine ran great for another 90,000 miles until there was more rust than body!

I think it's normal to find voltage on both coil terminals when the engine isn't cranking. If necessary, I can double-check on another one of my cars tomorrow. The computer pulls the negative terminal to ground like you think, and holds it there until it wants a spark to occur, then it opens the circuit to abruptly stop current flow through the primary. If it would hold that circuit at ground with the engine not running, that might overheat the coil and the switching transistor in the computer. Remember that air flow to cool it when the engine is running?

270 ohms for the pickup coil should be okay too. One thing you might consider is checking the air gap for that pickup between it and the reluctor wheel. It must be.018" and must be checked with a brass, (non-magnetic) feeler gauge. One time I couldn't get the rotor off to replace it so I cracked it with a hammer and screwdriver. When it spread open, it pushed the coil a little and I had a no-start. As I recall, the gap opened up to only about.022" but that was enough to cause a problem.

Just for fun you also might try laying the air cleaner housing upside-down with some tension on the wiring harness to see if you get spark. If you do, suspect loose solder connections on the computer's electrical pins. I haven't really run into that but there is a lot of vibration from the engine so I suppose it's possible.

If none of these things work I'll search for a service manual to figure out where to go next. Please don't scrap the car. They were way too nice and they're a lot more reliable than the newer stuff. If you think no spark is a problem now, wait until you have that on a 2005 model!


Caradiodoc
Apr 20, 2011.
Well I don't need much encourage not to quit. Once upon a time, I used to work on cars. My other "car" is a 1982 F250 with a straight six. Came with a complete set of service manuals.

On the Chrysler, given that the computer is cooled by airflow, is it possible that the module has become fouled by grime? The engine compartment on this car is pretty grubby.

The next question is: Where do I get a brass feeler gauge?

Also, is there a way to edit a response on this website?

Thanks for your help.


Tiny
Frozen Rebel
Apr 20, 2011.
Editing is no longer possible since they switched to this web site a few months ago. We used to have the ability to delete our own posts. Now many of us are posting all over each other and we can't undo that.

The guys who visit repair shops each week with their tool trucks have brass feeler gauges. You can use regular ones but they're steel and will stick to the very strong magnet in the pickup assembly. That makes it drag with a lot of resistance making it feel like you're measuring the gap. With the brass gauges, there will be no resistance unless it's from contact with the two parts. Since you may never use them again, you might ask at some local auto parts stores. Many of them now borrow or rent tools. If you have a friend who is a mechanic, he might have a set you can borrow too.

Everything in the computer is sealed in a sort of hard jelly. There will be some aluminum heat sinks sticking up to catch the air flow. Dirt is not an issue. If it was, the problem would be common and well-known.


Caradiodoc
Apr 20, 2011.
Well I gave up on it last night before I got your previous response, and as soon as I left, they used a free tow with insurance to get it pulled around the corner to a shop. Well would you believe it started right up for the shop? I guess I didn't try hard enough to get the thing started, or I should have pulled a plug and checked for a spark after banging on it with the hammer. Bottom line, I will stick to my day job. Thanks again.


Tiny
Frozen Rebel
Apr 21, 2011.
Darn the bad luck! Hope it stays running. Keep me posted.


Caradiodoc
Apr 21, 2011.