92 Fuel pump probs-need more info

[Georgia Snake]

First of all Jrichker, thank you for the info so far. I have followed your troubleshooting but havent determined the problem. To readdress what my problem is I will discribe the symtems again.
I have spark.
Switch in the RUN position
PCM Power Relay closes
Fuel Pump Relay closes
Fuel pump does not run
OR most of the time I have this symtem
Switch in the RUN position
PCM Power Relay closes
Fuel Pump Relay closes
Fuel Pump runs continuously

The Fuse links are fine
Inertia switch not tripped
I have fuel pressure (when the pump runs continuously)
I have Voltage to the Fuel Pump Relay
I have Voltage to the PCM Power Relay
Wiring between the Fuel Pump Relay and the PCM checks good
The computer checks good (power at pin 22)
The "light blue/orange" wire checks good no short to ground

Ok I am a good troubleshoot on a hunch type of mechanic when all else seems to be failing around me but at the same time I would really like to be able to prove my hunch. I really suspect the computer is bad but I am open to anything else that can be checked.

Bill Miller
Columbus GA

 

[HISSIN50]

Nicely written out.

Have you determined that the FP relay is working at all times? When the pump runs non-stop, I'd probe the FP relay terminals. See if the control side has 12 volts and ground, or if the relay is simply latched.

By the same token, when the FP wont come on, see what elements are missing (you'll either have to test for the computer-supplied ground to the relay coil and [once it's known to be good] then ground that part of the circuit at the self-test connector, or test quickly during the prime-out period.

I'm sure JR and others will have some very good advice.

Good luck Bill.

 

[jrichker]

Go back and read the theory of operation again. Once you understand how it works, it is much simpler to troubleshoot.

Jumper the fuel pump test lead to ground when the fuel pump does not come on like it should. If it runs then, the fuel pump and relay are good. If fuel pump does not run, then they are suspect. Use a voltmeter to verify power to the fuel pump at the relay and again at the connector at the back of the car.

If the fuel pump does not run, and you have good fuel pump power at the connector at the back of the car, the relay wiring to the computer is bad or the computer is bad.

 

[jrichker]

Fuel pump runs continuously: The light blue/orange wire has shorted to ground or the computer is defective.
Disconnect the computer and use an ohmmeter to check out the resistance between
the light blue/orange wire and ground. You should see more than 10 K Ohms (10,000 ohms)
or an infinite open circuit. Be sure that the test connector isn’t jumpered to ground.

If the wiring checks out good, then the computer is the likely culprit.

Prior to replacing the computer, check the computer power ground. The computer has its own
dedicated power ground that comes off the ground pigtail on the battery ground wire. Due to
it's proximity to the battery, it may become corroded by acid fumes from the battery. It is a
black cylinder about 2 1/2" long by 1" diameter with a black/lt green wire. You'll find it up next
to the starter solenoid where the wire goes into the wiring harness