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Random stalling

96 grand cherokee 4.0L- Randomly stalls or maybe I should say it randomly operates. Hot or cold it doesn’t matter. Sometimes it will restart sometimes not, This has happened before and I replaced the computer- twice. It works fine for a while but I end up here again. Any ideas on what could be frying the computers. Is there a way to check the computer to see if it is malfunctioning?


Why are you so sure the PCM was faulty?

That is usually the last thing to do, after all other possibilities have been ruled out.

Have you hooked up a fuel pressure gauge?

Have you retrieved any fault codes?

Have you checked if the ignition switch is cutting out?

Last two times we went through everything. Followed all the codes through the whole ignition system and rplaced coil and distributor, sensors etc. Ruled out everything else. Unfortunately there is no way to check the computer itself except rplace it. Trying to avoid spending $500 and a lot of time chasing shadows.
What igniton switch are you referring to? The one on the column?
What might cause a computer to go bad? Too much voltage? too little? bad ground?

The most common cause of ECM (computer) failure is broken solder joints. Caused when the circuit board gets hot from the temp of the passenger compartment. The wire traces expand with temp at a different rate than the circuit board material. Sometimes the solder joints can be fixed. Try one of those places like Module Master maybe, which will fix a defective ECM. In the summer try to park in shade, avoid parking in full sun where the passenger compartment gets super hot. Do you live in a hot climate? I expect cold can do this too, but it would have to get very cold probably, like in Alaska or something for the same thing to happen.

If you’re sure the ECM is indeed the problem, one would imagine that bad spikes on the voltage the alternator puts out could prematurely age and eventually destroy the ECM.

Improperly filtered or regulated voltages from a bad alternator or regulator could easily exceed the 12V line by 10 fold. You wouldn’t be able to see it because regular multimeters are just too slow to see these fast rising and falling edges.

If you have access to an oscilloscope or know someone that has one, check that level.