Is there no alternative to the ICM? (Page 1/2)
Yorgle DEC 14, 04:30 PM
Over the past year or so, my 86 iron duke has eaten no fewer than six ignition control modules- all from various sources, high buck ones (including an NOS GM), low buck ones and several in-between. The outcome is always the same, install new ICM and it starts/runs great for a few weeks/months, then random hard starts/missing for a while, followed eventually by dead on the side of the road. No codes, no other problems. Plugs and wires replaced, gapped, inspected, etc several times without effect. I even replaced the distributor with a new one. Each time, I used the the heat sink paste, cleaned and inspected leads, connectors, grounds, etc. Yet the pile of dead ICM's grows.

So... has anyone found anything better from GM or aftermarket ? I've searched pertronix, MSD etc without success.
theogre DEC 14, 09:39 PM
Blowing ICM like that Is Not an ICM problem but 1 or more other things are causing ICM death.
Can be issues on low volt side, high volts side or combi of both.

Just 2 Example:
F'd plugs or wire to them can "short" high volt anywhere often frying the Coil shorting internally then fry ICM.
Many install ICM wrong w/o silicon or heat sink grease &/or use crap screws cause crap Grounding for ICM both can kill it.

See cave https://web.archive.org/web...t/~fierocave/hei.htm & electric section.

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Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave

Spoon DEC 14, 10:01 PM
After that many ICM replacements, it would seem the problem is elsewhere. The ICM is being affected by that problem. Example, when I purchased my 86 2.8 I had a break-down several weeks later. It was as if someone turned off the ignition switch. I steered off the road to a safe area and popped the decklid. Battery cables were clean & tight, I wiggled the wire harness around the dizzy area. All seemed ok and the engine started up with no issues.
This happened a few more times over a long period of time (several months) as I recall.

Long story short, I began tugging on wires while the engine was idling including right up to the ECM behind the center console. Bingo!!, it was a wire at the connector to the ECM. I could move it using an ink pen and the engine would hesitate. I believe it was a white wire that led to the ICM connector. I used an ohm meter to check that wire for continuity end to end. Recrimped as required and never had an issue since. Perhaps high resistance in that wire could kill an ICM .

Spoon

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"Kilgore Trout once wrote a short story which was a dialogue between two pieces of yeast. They were discussing the possible purposes of life as they ate sugar and suffocated in their own excrement. Because of their limited intelligence, they never came close to guessing that they were making champagne." - Kurt Vonnegut

theogre DEC 14, 11:07 PM

quote
Originally posted by Spoon:
Long story short, I began tugging on wires while the engine was idling including right up to the ECM behind the center console. Bingo!!, it was a wire at the connector to the ECM. I could move it using an ink pen and the engine would hesitate. I believe it was a white wire that led to the ICM connector. I used an ohm meter to check that wire for continuity end to end. Recrimped as required and never had an issue since. Perhaps high resistance in that wire could kill an ICM .

Iffy Wire(s) to/from ECM won't kill the ICM but sure won't help.

Think White is ECM Timing to ICM after ECM controls timing after starting the engine & only 5v pulses.
Cliff Pennock DEC 15, 01:54 AM
While all of the above can be true, don't underestimate the absolute crap quality some brands' ICMs are. I used to go through ICMs like crazy too until I stopped being a cheap-ass and got myself an ICM from a reputable brand - which was quite a bit more expensive than the ones I used to buy. Haven't had a problem since (and I'm guessing it was 15 years ago I replaced that ICM).

PS: Can't remember for the life of me which brand it was unfortunately...
Cliff Pennock DEC 15, 02:05 AM
Oh - didn't read properly. You already tried the expensive ones. Still, it could very well be that if you get an original from a junked Fiero or so, it will last a lwhole lot longer.
MarkS DEC 15, 06:57 AM
1st thought was an NOS GM but that died too and that's not easy. Just a guess but have you tried replcing the coil? It could be there is some high voltage leakage into the coil primary to a degree that it functions but will eventually fry one of the semiconductors in the ICM.
fierofool DEC 15, 10:20 PM
Any of the secondary ignition components can put a strain on the ICM. Bad wires, plugs, or even the ignition coil can cause a failure. A weak pickup coil in the distributor can be at fault, too.
Patrick DEC 15, 11:09 PM

quote
Originally posted by fierofool:

A weak pickup coil in the distributor can be at fault, too.



Agreed. Replacing the pickup coil (which is quite inexpensive) is advisable any time the ICM is replaced.

Vintage-Nut DEC 16, 10:37 AM

quote
Yorgle:
I even replaced the distributor with a new one.



As fierofool and Patrick suggested; replace the aftermarket pickup coil.

When I recently rebuilt my OEM distributor; I bought GM / ACDelco parts......

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Original Owner of a Silver '88 GT
Under 'Production Refurbishment' @ 136k Miles