Fuel Supply Issues

[indyglideman]

My 1994 Explorer will not start. I checked the inertia switch it is closed and good. Checked fuel pump relay coil is good, relay changes state with 12 dc applied to the coil, and the normally open path closes with 12vdc applied to the coil. So like a fool I replaced the fuel pump. Truck still will not start. I then checked the connections in the relay/fuse box under the hood. The terminal for 12vdc supply from the ECC relay goes to 12vdc when the key is on, this I assume is the positive side of the relay coil. The negative side of the relay coil connection does not show a reference to ground. In fact this terminal shows 1.24vdc positive when read with a meter.

Does anyone know where this reference is coming from and why it would be positive? The wiring diagram shows this as a connection to the diagnostic connector and to the PCM.

How do I troubleshoot this?

 

[geoph1986]

I just recently went through this, my problem was a bad contact in the relay box. Will the fuel pump run by jumping the self test connector?

EDIT: Here's the thread that I started and the info inside became quite valuable to me. MrShorty is an electrical god...well maybe not a god, but he's pretty damn smart.
http://www.explorerforum.com/forums/showthread.php?t=255098

 

[indyglideman]

It is raining here and nasty so i will not be under the hood for a few days. I have read the thread listed above and can see that it must be the pcm that controlls the ground side of the relay coil to turn on and off the fuel pump relay and hence the pump.

So if i ground the test connector and the pump runs, does that mean that the pcm is bad?

I was looking on alldata and there was refrence made to the HEGO sensor being bad causing the pcm to show a positive on the coil. Is this a valid statement, can a HEGO cause this situation?

If it passes the grounding test and still will not run on its own, what is the next step?

 

[geoph1986]

So if i ground the test connector and the pump runs, does that mean that the pcm is bad?

It would mean that you have a fault in the PDB, between the PBD and the PCM, or possibly the PCM itself (which I would suspect last). When you turn the key to the run posistion, does the "check engine" light come on? If it doesn't, that indicates that the PCM isn't getting power. If the PCM isn't getting power, the self test for the fuel pump won't work either. Have you checked the PCM (EEC) fuse in the PBD (it's fuse #4, 30A)? Or even the fuel pump fuse (I believe it's the 20A mini, in the PDB)? I had my truck ripped apart trying to trace down my fuel pump problem, and in the end it turned out to be the connector on the fused side of the EEC fuse in the PDB. I hope this helps you find your problem. Electrical issues are a PITA! Good luck

P.S. Also don't forget to make sure your grounds are good. Not just at the battery, but where they ground to the fender, and where the PCM grounds to the kick panel.