Alright I bought my 94 vette a couple of weeks ago. In a couple of days I had achieved to put about 500 miles on it. In the last 50 of those miles it would just die for a millisecond then come back to life and then the check engine came on. I read up on here how to pull the codes and I did. It had a H36. I looked it up and figured out it was the optispark. The guy before me had installed an msd coil and optispark, so I called up MSD and waited 3 weeks to get a part back. 2 days ago it arrived and I threw it inside the car. Before installing the water pump I cranked the motor just to insure that the optispark would work before I had to repeat everything again. My wife and I heard it run, it ran for a total of 10 seconds before I turned it off with the key. My wife and I installed the water pump and got everything plumbed, and shortly after tried to fire it up again to test drive it. The thing cranks but no fire. I diagnosed it by proving no spark at the plugs, took a spare spark plug wire and proved that the coil wasn't sending any juice to the optispark. I pulled the code and it was a H41. I researched and realized it meant a break in the wire between the ICM and the PCM. So I shot the wire and it reads just fine through the ohms meter. So just for kicks I jumped it right off the PCM (B5 pin) to the ICM white wire. After doing that my H41 went away but I got a H32,H34,H36,and a H38. I decided to take off my jump wire and test the stock wire again. Everything read fine on the OHMS so I cleared those four codes, tried to crank again and now the H41 is back but the other 4 disappeared. I have a new ICM in route to the local parts store. I am going to slave it in and see if it makes a difference. If it doesn't I'm leaning towards the PCM because its the only thing that I can't check and that is giving me the codes because its "sending" out the signal. I just want to make sure I'm on the right track and would like to hear second opinions.

Thank you
Rob

 

The PCM should I believe send a pulse through that wire every time that the PCM wants to fire the coil. If you have some sort of pulse, the PCM is good, if not pulse, maybe bad connection at the PCM or a bad PCM provided you are getting a proper signal(s) from the Optispark to the PCM.

If you are getting a pulse, put a test light around the power and ground wires at the coil. When you crank it, the light should flash, if it does not, then you have either a open circuit or high resistance in the circuit, or a bad ICM.

All these things can be tested.

 

You have a wonderful wife!

I had problems like that when I first got my Vette.
Looks like you have done good diagnostics. I am sure you know the "codes" are not pointing you in the right direction all the time, it can be basic problems also. I would do another check to see if your results are the same. You will figure it out.

 

I will wait to read your response to the new ICM before I add anything further to this post.

I hope that fixes it.

DUB

 

So after doing the ICM the code H41 dissappeared. But since I'm military and money can get a bit tight because of a move coming up I decide to plug back in the old ICM to see if the code would come back and it didn't. So I pulled a plug again and had no spark. Pulled the coil wire and barely got a spark. So I got another plug wire and hooked it from the coil to a spark plug and it didn't even give enough juice to spark the plug. So I decided return the ICM and get a new coil to slave in Friday morning after work. After I did that it fired right up. Been driving it the last two days and it been doing just fine. Thank you for your input from all of you.

Rob

 

Great news. Hope you and your wife have fun with the Vette.
Thanks for ending the thread correctly.

 

Rob,
HECK YEA!!! Glad to read you had success. Gotta love it when a plan comes together.

DUB