ROBDSSA

I have a 1994 LT1 with 125K miles on it that has started to act up once it warms up. Cold start is excellent, drives great. Once temperature exceeds 190 degrees, the car stalls. It runs great right up to that point of stalling, then just shuts down and will not start until it cools enough. I checked one of the injector leads right after it stalled with a Noid and there was no signal. Once it cooled enough to start, the Noid started flashing. I've read about issues heat can cause to the Opti, the coil, the injectors.... Anyone have an idea before I start changing everything in hopes of tracing the problem?

94c4er

Check the Ignition Control Module (ICM) located with the coil. Autozone can test it, but make them run the test 3 times because it may show good the first time. Each time you run the test it will get hotter therefore it may be breaking down when heated. If you change it or re-install that one, make sure you use heat sink paste on the heat sink.

MatthewMiller

The ICM won't cause the injector signal to cease. Normally, I'd suggest that you have a bad sensor that only gets read in closed-loop PCM operation (it runs open-loop until it warms up), but again I don't know of a sensor that would cause the injectors to stop getting signals. In this case, the two things come to mind that could cause this: the optispark and the PCM itself. The PCM fires the injectors based on the crank position signals it gets from the opti. The sensor in the opti is known to have a heat-related failure mode at times.

Watch your tach when the car stalls - it is also informed by the opti sensor signals. Does the tach instantly go to zero or bounce all over the place when the car stall? If so, then I highly suspect your opti is bad. Also, next time to drive the car into failure, check to see if you have spark at the plugs. If not, again that implicates the opti. Another check would be to put an oscilloscope on the two signal wires coming from the opti to the PCM - no signal, bad opti. Here's a thread that explains that and also how to use an a/c meter to check for the signal.

OTOH, if you can confirm that the PCM is getting good signals from the opti and yet the injectors are not getting signals to open, then I believe that implicates the PCM itself.

ROBDSSA

Thanks for your input. Just to clarify on how the tach responds when stalling, if it bounces around is that an opti issue or if it simply falls to zero is that the opti issue?

MatthewMiller

Either, really.