95tealconvert

Wanted to share my story so all LT1 owners know why it is important to check your ICM and the mount plate it sits on. As a '95 LT1 owner I have heard many stories of the opti but seldom do you hear about the Ignition Control Module so when my '95 started having a weak spark issue and at times a hard start or even no start, my first thought was I might be having a opti issue.


I tested my system and found that the opti was working to spec. What I found was the original factory ICM heat sink compound had dried up after over 20 years of service which meant the ICM mount bolts were slightly loose and the ICM was now getting hot and failing. I replaced my ICM and car started right up and spark is now normal coming out of the coil.


Just wanted to share this with all fellow LT1 owners to make sure you have good heat sink compound behind your ICM as it will dry up over time.

92ragtop

Very easy to do. Just make sure you use Heat Sink paste and not dielectric grease or some other product.

John A. Marker

I replaced mine years ago and used a non-metal spacer between the engine and the heat sink to get less heat transfer from the engine.

CCRed

People miss this problem all the time!

TorchTarga94

That's all good and well, and glad you solved your problem. However I don't think we seldom hear about the ICM (I think we hear about it quite often). In fact, I would wager that most of the time when someone is blaming the opti someone steps in and says check ICM first (At least on this forum).

chatham

curious, what did you use?

PaZaicC4

What is the name and brand for the heat sink paste? Where do you find it?

Silver96ce

Google is your friend -

https://www.google.com/webhp?sourcei...eat+sink+paste

yd328

I just did this on my 95 as part of a tune up, it was dried up. The heat sink plate also got a good cleaning.

Gary

scotth48

I put a nylonn washer between the head and the bracket so it would not transmit some heat.

FAUEE

The head is the heatsink for the icm. This mod doesn't allow the icm to cool as much as it should.

scotth48

I used nylon washer. May have put a couple of stainless washers just to space it more wit a longer stainless bolt. Can't remember for sure.

auggy

Heat sink paste $2.00 for a very small amount at Advance Auto SL203. Check inventory before you go since it is not in all stores. The heat sink was greasy and clogged up on my 94. Two screws, one was loose, comes off easy to clean. Very small little used socket size. Can't believe GM bolted it to the head which gets really hot. Cool idea to put spacer behind heat sink (which I have not done). Looks like heat sink assembly also holds the coil but probably does not help to cool it. The ICM comes off easily where the coil looks to be much harder to get off, at least on my car. You could carry spares of both to get you home. Just plug the wires into the spare(s).

1993C4LT1

And good advice from the OP But what I don't get is when: someone mentions they have a code 16 or 36, and people say to get the ICM checked.

My car has no ICM, but it runs.

scotth48

Just to clarify that the nylom spacer went between the head and the coil bracket. The ICM is mounted on the heat sink which is mounted to the coil bracket and than mounted to the end of the head.

matt92

I'm very grateful I tripped over this thread. I was sure I was going to be replacing the Opti-Spark.

The car was breaking up over 5000 rpm and after it was good and warm anything over 2500 rpm it would develop a miss.

New ICM and all my problems vanished.

Whaleman

High Performance Silver Thermal Grease CPU Heatsink Compound Paste D6E6 X2T1 | eBay less than a buck-free shipping.

turbobuick33

Has anyone relocated the ICM to a different area in the engine bay?

Whaleman

Yes, If you do a search some have mistakenly made this move. Calm air is a very poor heat sink compared to being mounted (with paste) on a couple hundred pounds of cast iron cooled by water. If you want to move it you better mount it on a four pound hunk of copper with fins on the back side. Just my opinion. Dan

grandspt

I made a harness and purchased a decent sized heatsink for the ICM. I also left an ICM in the stock location on the cylinder head just in case the ICM on the heatsink ever fails. I can connect the one on the head easily and not get stranded.
I did some thermal readings of the ICM (with new thermal paste) mounted on the cylinder head and compared them to the ICM mounted to the heatsink on the radiator shroud. The ICM mounted to the heatsink on the radiator shroud runs way cooler.
However I don't recommend adding washers to keep the OEM ICM heatsink away from the cylinder head, as others have stated that little stock OEM heatsink is not going to keep that ICM cool! The ICM needs to transfer that heat away from itself.
GM mounted the ICM on the cylinder head for ease of packaging, but it certainly is not the best place to mount the ICM from an electrical engineering design.