Dead Computer and Can't find one


#1

My 1995 Jeep Cherokee seems to be dead! While driving, it stall late one night seeminhly not getting fuel. Had Gas, about 1/2 tank. When help arrived, I had two opinions that it was the fuel pump. OK, fix it. However, 4 weeks later, the Jeep isn’t fixed. It seems that the fuel pump is fine, it is the “computer” that controls the fuel pump that is dead. Can’t find one, any ideas?


#2

The computer may or not be dead (unlikely that is is dead), but it sounds like there is a lot of guessing going on here.
The fuel pump “seems” ok is a pretty shaky diagnosis.

The computer does not control the fuel pump directly; only indirectly through several fuses, fuel pump, ballast, and ASD relays, inputs from the ignition to the computer, etc.

It’s either guess at this or get a good troubleshooting manual (NOT Chiltons)or wiring schematic and follow the diagnostics step by step.


#3

The fuel pump circuit has a ASD relay,fuel pump relay, and the PCM. If one of these fails the pump will not run. You also have to check the wires and connecters. A poor connection or a broken wire to any of the mentioned components will cause the pump not to run.


#4

That was a good point about the ASD (automatic shutdown) relay. This relay responds, through the PCM, to several inputs such as the throttle position sensor and the crankshaft position sensor. If one of these sensors gives a bad reading, the ASD will not activate the fuel pump relay. It is possible that you could replace the PCM and still be in the same position. More troubleshooting is called for.