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How hard is it to change the ICM on a 93 LT1?

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Old 06-13-2018, 11:39 AM
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Justin Joyner
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Default How hard is it to change the ICM on a 93 LT1?

I have a 93 C4....it currently has this issue where it starts fine on a cold start, but if the engine gets hot, it fails to start. The local mechanic believes it to be the Ignition Control Module. Although he says it's a real pain in the *** to replace as it's located inside the distributor, and apparently it would cost over $1,000 to replace the part(s) in question.

Is this really where the ICM is? I see ICMs listed online for fairly cheap ($60-$70), so most of the cost to replace would be the labor itself I'd imagine.

So, is it really that much of a pain in the *** to replace?
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Old 06-13-2018, 11:47 AM
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aDigitalPhantom
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The ICM is on one of the Cylinder heads next to the coil. It's easy to change, and it doesn't take long.
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Old 06-13-2018, 11:56 AM
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Is this something I could do myself? On a scale of 1-10 of automotive knowledge/experience (with 10 being a real pro), I rate myself a 3.
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Old 06-13-2018, 02:53 PM
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It's on a bracket with the coil. There are two bolts holding it on, and I think 3 wire connections. If it hasn't been replaced before you might need to drill out two rivets, but that might be the coil. After that it's just remove the old, and add the new. When installing the new ICM make sure to use thermal compound on the ICM. You should be able to change it.

PS
Don't use dielectric grease. You want thermal paste, heatsink compound, or similar. It will cost more, but you can buy thermal paste from many places that sell computer parts.

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Old 06-13-2018, 03:31 PM
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DGXR
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Originally Posted by aDigitalPhantom View Post
The ICM is on one of the Cylinder heads next to the coil. It's easy to change, and it doesn't take long.
Yes it should be on the front of the right (passenger) side cylinder head.
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Old 06-13-2018, 03:41 PM
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This is for a Camaro, but it's basically the same thing.
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Old 06-14-2018, 07:11 AM
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All the above is correct. Your mechanic is right to suspect the ICM, but wrong in where it's located. I guess he's confusing it with the optical sensor inside the Optispark distributor? That sensor can fail with heat soak, too, but more often it's the ICM. Before throwing parts at this problem, I'd do some diagnostics to narrow it down. There is a good guide here: http://easyautodiagnostics.com/gm/4....test-the-icm-1. You'll have to do this testing while the car is failing to start, of course. You can also call your local parts stores to see if any of them still have the equipment to test an ICM - it used to be that they all did, but not so much anymore. If you find one, have them run the test a couple times to let the ICM get really hot. It may not show bad the first time they run the test on the cold ICM, but the test will get it hot pretty fast.
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Old 06-14-2018, 09:48 AM
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Justin Joyner
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Great info everyone, thanks! Super helpful!
@MatthewMiller I will follow your advice as well!
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Old 06-14-2018, 05:26 PM
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FYI - amazon is your convenient place to pickup thermal paste/grease from the comfort of your couch. As others have said, donít skip it.
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Old 06-15-2018, 11:34 AM
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ICM and thermal paste has been ordered. Will probably work on the car next week or week after.

How do I know how much thermal paste to apply?
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Old 06-15-2018, 02:42 PM
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Originally Posted by Justin Joyner View Post
ICM and thermal paste has been ordered. Will probably work on the car next week or week after.

How do I know how much thermal paste to apply?
It just takes a thin layer to squish between the bracket and the metal backing plate of the ICM. The idea is to have continuous material contact from the ICM to the heat sink in order to all the ICM's heat to transfer to the sink as efficiently as possible.
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