365021

Changed my Optispark 14 months ago with a brand new Summit Racing Optispark. The new Opti has about 7500 miles on it. 4 weeks ago, car would run great and then just stop running instantly. Would try to start immediately, and after about ten minutes, car would start and run normally and I would typically drive home with no more problems. This has happened to me about 10 or 11 times since then. It's always the same....Car starts and drives normally and then engine will stop running instantly. Wait about 10 minutes, car will start and run normally for awhile and then happen again. No codes present and there is plenty of fuel pressure. After reading many forums, I decided to replace the ICM. Purchased a brand new AC Delco ICM at Bennett Auto. On my way home, the car stopped running. Pulled over on side of road and decided to put NEW ICM in to see if car would start immediately. Unplugged old ICM and plugged NEW ICM in within 4 minutes. Car cranked right up! Drove it right home (about 7 miles). So now I think I've solved my problem, right? HAS to be a bad ICM, right? Get up the next morning car starts and runs great. Drive about 10 miles......and the car engine stops running instantly....DANGIT! So now I'm thinking it is the Opti. No codes, fuel pump works great, etc. Hard to believe it could be an Opti with so few miles on it and so little wear and tear on it......Before I replace Opti, just want to see if it could be anything else....What do my fellow Corvette Forum members think? By the way, my Vette is garage stored and I NEVER wash the engine. Great shape with 90,00 miles on it. ANY input would be helpful.....Thank you all.

RollaMo-LT4

I am sure no expert, but I don't think it's the Opti.
If it was, the car wouldn't start up and run so well most of the time.

It really does sound like a "heat sink" issue with the ICM.

Coves4me

365021, Before you point a finger at the Opti-spark or the new ICM you bought, have your coil checked out. It seems that your engine is fine when it is cool, but when it gets hot, it craps out. This is typical for a bad coil as the heat from the engine affects them. It's mounted just below the ICM. Also, check your coil wire and make sure it's in good shape and not grounding somewhere.

Good luck.

Mark

1986coupe

Take the ICM off and make sure that there is enough of the proper heat sink compound. Some people use die electric grease but that isn't the best for that application. If there is no heat sink compound there or very little it is possible that your ICM is fried. Quite common with that part.

It is hard to test the ICM because the problem often only shows up once it gets hot.

bjm206

Here are a couple of things you can try after it dies in order to diagnose.

1. An inline spark plug test light connected to the coil will allow you to see if the coil is firing while cranking. If the coil is firing consistently and strongly then it is likely that the coil, ICM, ECM and associated wiring are ok. If the coil is not firing then you will need to isolate each component including the distributor to see what is wrong. It would be best to get a factory service manual if you want to do this although there is a lot of info about doing this on the web.


2. If the coil is firing then connect the inline spark plug test light to one (or several) of the spark plugs, start cranking and see if the energy is getting through the distributor to the spark plugs. If the spark plug light is firing consistently and strongly then you will need to expand your search for the problem to the fuel system, etc. It would be best to get a factory service manual at this point. If the light is not firing while cranking then the problem probably lies inside the distributor.

kimmer

How did you change your ICM in 4 mintues?

corvetero

Sorry, but what is it the ICM?

365021

Unplugged the ICM on the heat sink and then just plugged in the other ICM and let it dangle.....Didn't unscrew any bolts

365021

Ignition Control Module.....ICM

365021

Alright Folks.... I replaced the coil (with an MSD brand) AND I went to radio shack and bought "Heat Sink Compound" for the heat sink. Someone on this forum also suggested to put two washers between the heat sink and the engine, not between the heat sink and ICM. Did ALL that and car started up and ran wonderfully.....until it got up to about 195 degrees on the engine.....then the car stopped running instantly just like it has for the last couple months. Tried to start car immediately after shutdown and car would not light off, it would just crank with no light off. Decided to take the washers off the heat sink.....took about ten minutes to do this. Then I went to start car and it lit off and ran wonderfully!!!! Then, at about 190 degrees F, car instantly stopped running. I have replaced the coil, ICM and ensured the heat sink was properly lubed up with heat sink compound and the car still stops running at random times. What the heck am I missing! Could it still be the OPTI? I mean, this engine runs great until it unexpectedly stops running. Any suggestions would be appreciated. Thank all of you for your replies.....

Tom400CFI

My suggestions would be to follow the gentleman's advice below that he gave in post #5

365021

I'll give it a try tomorrow or Wed and let you know the results. Thank you