I will admit up front to changing parts in the hope of solving the problem. Stupid thing to do without finding the root cause but that's what I did. Along the way I uncovered some things that were about to fail so it wasn't a total loss.

I have an LT1 from a 94 Corvette installed in my Porsche 968 as part of the Renegade conversion. The car ran great and the one day without any warning it died just as if the key was turned off. It happened just once and fired right up once after I coasted to the side of the road. It then drove fine for about 300 miles and did it again. Then it started doing it more often. The engine can be cold or warm. It can drive 100 miles without any issue and then act up without warning for the next 100 miles.

The optispark was changed approx 3000 mi ago and new plugs and Magnecore wires were installed.

I changed the ICM and coil. I made sure to use the heat transfer paste on the new ICM and have spaced the aluminum cooling board away from the engine.

The car drove fine for almost 900miles and I thought all was good then suddenly it started dying again. Now sometimes it would fire right up and sometimes not. A friend of mine who is an electrical engineer asked me to send him my PCM so he could see how the board and components were. It was so bad he was shocked the car ever ran. The traces on the board were lifting off and the layers making up the circuit board itself was separating. I didn't know where to get a PCM from but both Lingenfelter and Golen Engine recommended the same place. I got a rebuilt PCM and all was fine for about maybe 75 miles and it's dying again.

I've hooked up a fuel pressure gauge and while driving and even when it dies I have 43PSI.

I then changed the ignition switch because rather than stopping in the normal off, acc and on positions it sort of smoothly went from one to the other allowing you to stop anywhere in between. I figured the switch was from 95 and was worn. The problem still persists and is so random I don't know how to diagnose it.

I don't know what could be causing this and man after driving almost 900 miles I really thought it was fixed.

Any ideas are welcome at this point.

Thanks,
Ron B.

 

I should also have said there is no Mass Air Sensor. The engine runs on speed density. The air temp sensor was also changed as were both O2 sensors when the optispark was changed. The Opti is a GM part.

 

Do you have the ability to check codes from the PCM?

 

Unfortunately not. The dash readout doesn't exist for me and while there is a port for an OBDII reader I don't have one that can read the OBD1 or 1.5 codes that might be stored in the PCM. I don't even know if codes are even stored in the PCM on this car.

 

Having a motor swap into a different car makes everything harder.

Sounds like an electrical issue as a knee jerk reaction. I'd highly recommend finding a scanner or borrowing one. 94 is still obdi, 95 switched over to the obd1.5 which requires a special cartridge on a tech 1 scanner.

 

I could be wrong, but my understanding is that the heat sink plate for the ICM needs to touching the head with heat sink paste for the ICM to cool properly. If not, the ICM will overheat and fail. I'm fighting this same problem with my 93 LT1.

 

opti

My first quess
water leak?
replace drive sleeve coupler on water pump so it flows properly.

just my guess since you can't pull codes