How can you check the opti spark to see if you are loosing spark? The engine runs for 30 minutes and gets hot and then just shuts off automaticily. I have a 1994 LT1 with 68,000 miles. I already changed the ICM and IC and the plug wire to the IC and Distributor. The fuel pressure is fine and the fuel injectors are good.

Welcome to the Guru! I know that running the car in a dark garage like at night type dark, will let you see anything sparking that shouldn't be.

Yea, welcome.
Pull the codes usimg the dash buttons. The dsah buttons are explained in our tech section under "Engine".

That tech thread is for 92-93 but the buttons work the same.

Read this thread, the way to jump the diagnostic connector and the codes are on post 22.

Pull any codes and get back to us.
Good Luck.

What automatically shuts it down?

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MK - fixed a small typo... nothing big...

as for what shuts off sounds like the engine.

Most strange. I doubt the opti would do this, unless it was really tore up.

Is there sufficient thermal paste on the ICM?

Yeah that really doesn't sound like an opti related problem. The device is very mis-understood and all too often blamed / replaced when it is not the issue.

Ultimately the opti is a glorified distributor. Sure it's a flat goofy looking distributor but it's a distributor just the same with a cap and rotor. Generally this part of it either works or it doesn't, just like any other distributor. Even if it's badly worn you'll get a misfire, not an on/off style failure, but it won't set a code.

The other half of the distributor, the side that supposedly causes so much trouble, is the optical pickup. It's actually extremely reliable and accurate as well provided you don't get it wet. The opti just happens to be located where it can get wet. It's not a bad idea for a design, rather just a poor location. When this side fails you can get all kinds of things, you can get misfires and or no start conditions but it likely will set a code because the ECM is actively looking for the data it provides.

So as others have mentioned, check the codes. If you get an opti-spark high or low res pulse failure then MAYBE the opti is at fault. If you do NOT get this code then it is very likely not the opti that's the problem.

If I had a lot of money I would like to start a website called "www.itsnottheoptisparkthatcausedyourcartoquit.com"

A lot of dim-wit mechanics have heard so many opti-spark horror stories that they'll blame a flat tire on them. If I had a dollar for every mis-diagnosed opti-spark problem I'd be making money in a very unusual way.

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Its what did mine in..found this out ..after I replaced the opti and it still didn't start. Put in a new ICM and paste and bingo...