LT1 owners check your Ignition Control Module
Thread Starter
Racer
Joined: Aug 2015
Posts: 375
Likes: 89
LT1 owners check your Ignition Control Module
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.
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.
Melting Slicks
Joined: Mar 2008
Posts: 2,351
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From: Delta B.C. Canada
2023 C7 of the Year Finalist - Unmodified
2019 C4 of Year Finalist (appearance mods)
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Very easy to do. Just make sure you use Heat Sink paste and not dielectric grease or some other product.
Racer
Joined: May 2006
Posts: 293
Likes: 29
From: Columbus Ohio
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.
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.
Melting Slicks
Joined: Jul 2011
Posts: 2,607
Likes: 205
From: Trinity FL
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).
Last edited by TorchTarga94; Apr 7, 2017 at 01:39 PM.
Heel & Toe
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Drifting
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From: New Jersey
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Burning Brakes
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From: Charlotte Michigan
Pro
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From: Baltimore County MD
heat sink
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.
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.
Race Director
Joined: Oct 2011
Posts: 16,097
Likes: 821
From: Dallas Texas
2025 C4 of the Year Finalist - Modified
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).
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.
Burning Brakes
Joined: Apr 2009
Posts: 1,185
Likes: 33
From: Charlotte Michigan
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.
6th Gear
Joined: Apr 2021
Posts: 6
Likes: 1
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.
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.
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.
Safety Car
Joined: Mar 2017
Posts: 4,213
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From: LeClaire Iowa
High Performance Silver Thermal Grease CPU Heatsink Compound Paste D6E6 X2T1 | eBay less than a buck-free shipping.
Safety Car
Joined: Mar 2017
Posts: 4,213
Likes: 1,330
From: LeClaire Iowa
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
Drifting
Joined: Jul 2004
Posts: 1,359
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From: MA
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.
