I have been trying to help get a friends Creamsicle running. Was running poorly and shutting off and not starting back up till it cooled when we started. Replaced all the vacuum lines with the kit from AA and replaced the MPS with a torn diaphragm with a known good one that we leak down tested. Car runs and idles fine but now it just still shuts off and won’t start back up. We aren’t even sure temp matters. It may be random. We tightened all the grounds but still can’t get it to stay running. Once it starts it seems like it would idle forever. Try to take it around the block and we are dragging it home. We put a fuel pressure gauge in line at the drivers side rail and 30psi steady. We are thinking about swapping the entire wiring harness out with one from a car that converted to carbs. Any other suggestions??

Did you check CHT as well as the wire from CHT to ECU? Look for shorts.

I agree, if the fuel pressure is steady. No reason to replace the harness. Make sure the grounds are firmly connected, and when it starts to quit see if you can get it to continue to run with spray gas if not it is either flooding out or an ignition problem

Always runs with starting fluid into the air filter housing so I think ignition is good.

CHT = cylinder head temp (sensor). Not ignition related. If it’s bad, or if there’s a short, you will get symptoms similar to what you are describing.

This is why you don't throw parts at it.

If it runs....

Can you verify the fuel pump keeps running?

Yes we verified pump running and 30psi steady at the drivers side rail. It’s there when running and when it’s stalls and won’t start right back up. Never fluctuates.

I am very good with a multi meter but I just don’t know enough about this system to know what to check for. I feel like it’s an electrical problem keeping the injectors from firing.

I am very good with a multi meter but I just don’t know enough about this system to know what to check for. I feel like it’s an electrical problem keeping the injectors from firing.

You said you replaced the MPS.
After replacing the MPS in my car, I also had an issue with restarting my car after driving it, and it ran badly. Turned out that the car was running way lean. After calibrating the MPS correctly for the right air/fuel ratio, the problem went away.
Even if the MPS isn’t the main source of the problem, it needs to be calibrated for the car to run right and not run at temps that will cook the motor.