gettin_dirty_with_ruby

How can I check if the PCM / ECU is bad?

Background:
1992 Jeep Cherokee Laredo with an automatic transmission
My Jeep died while idling in the driveway. I tried to start it but didnt hear the fuel pump kick on. Replaced the fuel pump and when I turn on the key, I hear the pump turn on and off. Put a gauge on it and I have 40 pounds of pressure at the rail, but it will not start. Thinking it might have jumped time, I put a timing light on it and no spark.... A buddy believes the PCM / ECU is bad. How do I check it and any other thoughts on what to look for?

If it is bad, anyone have a used one for sale?

salad

Your buddy needs to learn how a computer controlled vehicle works. There is absolutely no reason to suspect the PCM is bad.

1. Does the ignition coil get power?
2. Are there any blown fuses?
3. Do the relays test okay?
4. Does the battery test okay?

(I think OBD-I fuel pressure spec is 49 PSI but I may be wrong)

RTorrez1

^^Check out the above.^^
91 should have 39psi +or- 5psi

gettin_dirty_with_ruby

1. Does the ignition coil get power? no power at the distributor
2. Are there any blown fuses? no blown fuses
3. Do the relays test okay? yes
4. Does the battery test okay? yes

cruiser54

Could be a bad CPS.

How did you test the relays?

Your test for power at the distributor?

gettin_dirty_with_ruby

I forwarded your comments to the mechanic and he went ahead and ordered a new PCM, plugged it in and my jeep fired right up.

Thanks for everyone's help and assistance!