'97 5.0 V8 will not start, no fuel at the rail

My '97 will not start, no fuel at the rail, can not hear the fuel pump run when turning the key on. Found 20 amp mini fuse "fuel system, anti-theft system" blown. Replaced fuse, still no fuel at the rail and no pump operation. Checked power at the inertia switch, unplugged, there is power at the dark green/yellow wire coming from the relay. But if I connect the plug to the switch, then have no power at the DG/Y wire. Put a jumper across the DG/Y wire to the Pink/Black wire, as soon as I plug into the P/B wire, the voltage goes away. The fuse has not blown again. I am thinking it must be a bad fuel pump but hate to drop the tank before I am sure of the fault. Any help or suggestions much appreaciated. Thanks
Don

Sounds like you might have some corrosion in the circuit somewhere. As soon as you load the circuit, the draw causes the voltage to drop. Are you using a multimeter or a test light to check for voltage? A multimeter has high input impedance meaning it barely loads the circuit. This is good for most measurements, but makes it difficult to find circuits with little load carrying capabilities.

You could try a test light and see if the DG/Y wire is able to brightly light the test light. If it does, then you should check the feed to the fuel pump for low resistance to ground. If it were currently a dead short to ground I'd expect it to again blow the fuse. If it's just a low resistance to ground, it may take it awhile to heat the circuit enough to blow the fuse, but still load the circuit enough to cause the voltage to appear to drop.

While none of these measurements will tell you where the problem is, it will at least help you determine where to start looking.

-Rod

Thanks for your help Rod. I tested power to the inertia switch with a multi meter, only getting 6 volts. I tested with a 12v bulb, would not light. The relay does click when turning key on. Tested relay plug with key on, one connection has 12 volts, two connections have 6 volts. I could not feel a click on the PCM relay or the WOT A/C relay. NOTE: this problem developed after I changed the turn signal "multi position switch". The switch seems to be working ok and I can not find any wiring problems around steering column that I might have caused. Could this new multi position switch be causing the problem or is it just a coincidence? I have thrown away the old switch so can not put it back in to test. Also my OBDII gage will not read faults, it powers on but will not continue to the "C.A.N. OBD2" window. Don't know if this is also related. Again, thanks for your help.
Don

If the test light won't light, I'd say you have a connection somewhere that is limiting current to the circuit. That would explain the 6V reading as well. You should have full battery voltage on the DG/Y wire at the inertia switch. You might try pulling the fuel pump relay and measuring the resistance between terminal 5 and the DG/Y wire at the inertia switch. You could also measure voltage on this terminal with the key in the run position to see if you still see 6V. The wire is spliced and goes to both the inertia switch and pin 40 of the PCM. The low current voltage you are measuring may be due to a pull up in the PCM.

With the key in Run you should have battery voltage to two terminals for the relay, terminals 1 and 3. These are probably relay terminals 85 (or 86) and 30. When terminal 86 (or 85) receives a ground from the PCM, the relay should close and provide battery power to relay terminal 87. You mentioned you only have 12V to one terminal for the relay. Did you have the key in the Run position when making that measurement? The terminal for relay pin 3 (30) should have battery voltage all the time. Terminal 85 (or 86) would only have power with the key in Run or Start.

I suspect there is no correlation to replacement of the multifunction switch, unless in the process you managed to disconnect or damage the PATS antenna around the key cylinder switch.

-Rod

I suspect there is no correlation to replacement of the multifunction switch, unless in the process you managed to disconnect or damage the PATS antenna around the key cylinder switch.

-Rod

just an opinion...1st rod your proboly right
but when coinsedences show up especially 3 i start to wonder

Rod thanks for your help, my explorer is up and running again, it was a bad fuel pump. I put a 12v jumper to the PK/BK wire at the inertia plug and the pump did not run. I replaced the pump today and it runs fine. The mistake I was making; I was checking for voltage at the DG/Y wire at the inertia switch with the key on (6v) but not doing it during the first few seconds when the ign switch was turned on. I checked it again, when the key is first turned on the voltage is 12v but drops back to 6v within a couple seconds (normal). Don't know why they keep it at 6v with the pump not running. At the relay plug with the key on it has # 30 = 12V, # 85 = 12V, # 86 + 0V, # 87 (to inertia switch) 6V. Thanks again for your replies and help.
Don

Thanks for the follow-up post, and congrats on getting your Explorer running again! I'm disappointed in myself for not mentioning that the pump will only run for the first couple of seconds after the key is turned to run, and only if several seconds have elapsed since the key was turned off.

-Rod