87350IROC

iTrader: (2)

Guys,

I have replaced 4 ignition control modules in the last 1 year and 2000 miles. Each new one lasts less time than the previous. It is obvious that something else is causing these modules to fail.

First module failed and was replaced with a GM module and the pickup coil was replaced with a GM pickup coil. Starting with this replacement I started using CPU silver thermal compound as I would imagine it is far more effective than the white goop (dielectric grease?) that comes with the modules.

Second module failed and was replaced with a GM module.

Third module failed.

Fourth module failed. I replaced this module with a GM module and replaced the coil with a GM coil and I added a 12ga ground strap going from one of the Module mounting bolts to an existing body ground. This should ensure the distributor is well grounded. This module lasted only about 100 miles.

I was really hoping the new coil + grounding strap would solve my problems. However the fourth module failed yesterday. I had to replace this module on the side of the road, so I just used the supplied thermal grease. So what else could it be?

Alternator voltage regulator? (volt meter looks good, but maybe its allowing an occasional spike.)

Bad ground to coil?

Any other ideas?

Thanks guys, I'm not driving the car until I find a smoking gun.

camaronewbie

Not sure about the "culprit", but I've always been told that the MSD brand is the way to go.

87350IROC

iTrader: (2)

Guys I could really use some ideas here.

I had some damage on the 4-pin metri-pack connector going into the ICM. So I replaced the connector and took the car for another drive. I blew another ICM in under 100 miles. So that obviously wasn't the solution.


camaronewbie,
Its not the modules' fault. There is no way the GM modules only last 100miles.

TTOP350

iTrader: (8)

Are the screws that ground the module rusty? I did a quick search (Im not n my garage w the GM service manual). the mod grounds to the base and thru the the ECM.. maybe the ECM or coil is over volting the mod somehow?
Maybe have to do the wiggle continuity test on all the module wires all the way 2 the ECM...

87350IROC

iTrader: (2)

Nah, if you look at the progression in my first post, you will see that I have swapped in a new GM coil and i have added a 12ga ground from the module to a body ground. The distributor and all components look clean and new.

TTOP350

iTrader: (8)

Yeah I saw that but just kept typing.. man im getn old

Andre.devillier

Please tell me you found the problem, as I have the same problem, replaced the coil, ht leads, even the dizzy no joy. 28 miles down the line I blew the Accel 300 ignition system, changed back to standard, 40 miles later pop goes the Module.
Now I am considering replacing the wires to the computer, maybe I must replace the computer, I am at wits end and in South Africa and have to import all the spares.
Please Help

87350IROC

iTrader: (2)

Andre,

I have not figured it out yet. Currently thinking maybe an alternator voltage regulator/rectifier failure. Which may be allowing to much voltage or A/C voltage into the system. The only reason I mention that is because with my key on / engine off I hear a slight electrical hum in the alternator. Doing some searching on the internet leads me to believe the hum may be a sign of regulator or rectifier failure.

Good luck with your car.

oddscrounger

My 87 IROC keeps throwing code 42 at me... quick question...

You say you went through for ICMs... how did you know they were bad? What was the symptom? Cuz my car starts and runs fine, but I can't get rid of code 42.

vetteoz

iTrader: (13)

Have you followed the diagnostic procedure for the code?

http://www.chevythunder.com/est_code_42.htm

oddscrounger

wow...

I am going to do this next weekend with a good friend of mine who is a little more well versed in working on cars. I am learning a ton since last June when I bought my IROC and have done a lot of stuff myself with a little bit of reading and trial/error. This is super helpful and I will take care of that code 42 and let you know what I found.

Really appreciate it.

oddscrounger

I guess my other question is...

What happens that is a clear sign your ICM is bad? Cuz this guy says he went through four. I had a full tune up done (cap, rotor, plugs, wires, timing... etc) and they said they couldn't clear the code 42; he said either bad or aftermarket module that maybe the ECM didn't recognize. Or maybe those mechanics weren't well versed in late 80s TPI setups, though that'd be hard to believe as it was a certified Chevy shop that's been around since 1913...

And how come, if they replaced my cap n rotor, they didn't replace the ICM? This is why since then, I've done everything myself.... ehhhhhh

vetteoz

iTrader: (13)

Be aware a code means there is a fault in that system and the computer is not seeing what it expects to see.
It does not mean just or only the item / device in that system is faulty ;
could be bad wiring , bad connections , bad grounds , etc

Bookmark this link , it may come in useful in the future
http://www.chevythunder.com/Flow%20c...0Chart%20Pages

oddscrounger

precisely... i'll use that chart to figure out what the problem is, whether it be a connection, wire, or the ICM itself and i'll post what I find

hitman0187

The telltale sign that an ICM is bad is the car will either shut off or not start when its hot. There are supposedly tests that autozone can run to determine if a module is bad however I have had ones test good and not work.
As a side note as part of a tune up the ICM wouldnt normally be changed.

ZZ3 Z28

I put in an Accel control module 35363 that lasted about 3 weeks before it took a dump. I reinstalled the original 26 year old GM module and the car started right up.

If any one here has a definitive answer on this topic I'd like to hear it.


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oddscrounger

This is interesting, because before I had my car fully tuned up it would start cold no problem if I turned it off and tried to re-start it while still hot, it wouldn't start. See thread... https://www.thirdgen.org/forums/tech...arts-cold.html

I still have the original distributor with the old ICM on it from the owner I bought the car from. Maybe I should put the old one back in? It's interesting that you said the GM original worked better than the aftermarket. Also, I have the code 42 but my car runs fine. Only issue is runs a little rough (stumbles, pops) when the car is cold but runs like butter when warmed up. And it breaks up/loses a little power just a tad at higher RPMs... but something tells me that's because the TPI setup is naturally weak at higher RPMs.... thoughts?

ZZ3 Z28

With the Accel unit installed the car shut off like turning off a light switch. One minute it was running, then off. No warning, no nothing. Dead. I have an Accel replacement module on the bench but I will examine the dizzy for anything extraordinary before putting it in.

After finding this thread I now think something wrecked it not that it was a defective unit.


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abray1

I burned up 2 about 6 years ago almost the same day (for a 91Z) and I bought a new distributor from ebay for $55.00 and it fixed it.

ZZ3 Z28

So what do you think was different from one dizzy to the next?

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vetteoz

iTrader: (13)

We torched 3 in 6 weeks ( weekend driving only ) before I found out that a failing coil will trash the ICM.( had never seen that documented previously)