Another burned up ICM...

Thank you! It’s been a few years since I’ve even seen a bull, let alone been able to take a shot. All kinds of luck helped with this one. We were just about done processing a spike my friend had shot, when I heard this guy come walking up about 80 yards away. So lucky he didn’t bust because I had to drop everything I was doing, get my rifle, and try to find a lane through the trees to get a shot. We weren’t being quiet the whole time either.

I was reading up on Third Gen about ICM issues and they also mention if a rogue spark grounds down to the distributor instead of going out to the spark plugs, that will fry an ICM also. I may be misremembering, but I think I had the center electrode in the cap broken in half and fall out when my last ICM failed. I’m going to check this cap for damage also when I get a chance to dig into it.


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Ya know, on Vortec engines the ICM is external with a fat heatsink on it, and they still fail more than one might think they should. As a nice coincidence, they are also known for the caps failing internally and misfiring. Hmmmm...

Richard

My camaro used to EAT ICM's, it was crazy. I popped one every few months before I figured out the problem.
I replaced my coil once, and my ICM multiple times.

One day the battery dies and will not charge, I took it out and found it had a small crack on bottom-side and it was shorting out internally. This caused spikes in the system which slowly ruined my coil and killed ICM's throughout the process.

New battery, no more issues.

I was never quite sold that it was just the short that killed them though, because I noticed that all the parts store ICMs I purchased (NAPA, Advanced, AutoZone) came with dielectric grease, which is WRONG. ICM's come from the factory with white lithium grease which helps dissipate the heat, dielectric grease does not. I think this also contributed to the mulitple failures because the final ICM that I put on the car was an AC-Delco ICM and it came with white lithium grease.


Long story short - check your grounds, look for any shorts, and use white lithium grease(or another similar heat sink compound).

It's not white lithium grease. It's heat sink compound, which is white, and it's very similar to dielectric grease, which is simply a silicone grease - but it has added materials (ceramic) that help it transfer heat. That's probably why dielectric works OK for some people. I personally would not use plain dielectric, but instead strictly use heat sink compound in this application. I have not ever had problems with modules crapping out on me at all.

Richard

computer processor heat sink compound, and clean, check little hole w/strainer vent at bottom of housing

I just showed my sweetie your elk. She says that she is jealous.

someotherguy said:

It's not white lithium grease. It's heat sink compound, which is white, and it's very similar to dielectric grease, which is simply a silicone grease - but it has added materials (ceramic) that help it transfer heat. That's probably why dielectric works OK for some people. I personally would not use plain dielectric, but instead strictly use heat sink compound in this application. I have not ever had problems with modules crapping out on me at all.

Richard

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Whoops! You're totally right, I was thinking about something different and just remembered the color (doh!). I actually used some heat sink meant for computer components the last time I put the Z28 together and it works like a charm (I still keep the tube, a flathead screwdriver and two ICMS in the glove box just in case haha).

I took the distributor cap off tonight and it looks to be intact. I’ll take the ICM out the next chance I get and have it tested.


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Got a new AC Delco ICM put in tonight, and it fired right up. I’m 95% sure that the module I installed, a D1943A, is a 369 module. In addition to the module, I modified the Spark Latency table to be the same as a vehicle that a 369 module came stock in. It started a little rough, but drove great. Idle smoothed out after more driving and warming up. I may need to add some spark advance at low RPMs to smooth it out.


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