Fuel pump wiring problem
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Fuel pump wiring problem
Working on a 1988 F-250 302 EFI Single gas tank. I thought I had a fuel pump problem because it stalled out on me one day and it would not restart. I checked the fuel line and was getting no gas to the injector rail. I figured that because I was seeing no gas at all, the low pressure pump in the tank had gone out. My thinking was that if the high pressure pump had failed, the in tank pump would at least squirt a little gas out. That may or may not be a correct assumption. Maybe someone can tell me if I assumed wrongly.
I replaced the low pressure pump and I still have a problem. I replaced the fuel pump relay and it didn’t help. I cut the inertia switch out and spliced the wires together. Right now, if I put a meter on the brown wire at the inertia switch without splicing it to the fuel pump wire, I get voltage when I turn the key on. If I splice it to the fuel pump wire and turn the key on, I get nothing.
I’m doing something stupid here but I just can’t see it. All the schematics I see include a tank selector switch. There is no tank selector switch.
Can anyone enlighten me?
I replaced the low pressure pump and I still have a problem. I replaced the fuel pump relay and it didn’t help. I cut the inertia switch out and spliced the wires together. Right now, if I put a meter on the brown wire at the inertia switch without splicing it to the fuel pump wire, I get voltage when I turn the key on. If I splice it to the fuel pump wire and turn the key on, I get nothing.
I’m doing something stupid here but I just can’t see it. All the schematics I see include a tank selector switch. There is no tank selector switch.
Can anyone enlighten me?
Fleet Owner
Joined: Oct 2005
Posts: 20,789
Likes: 1,753
From: Kentucky
The fuel pump relay is energized for only a few seconds when you cycle the key from Off to Run. I suggest you jumper pins 2 and 6 on the Diagnostic Data Link to turn the pumps on full time so you can troubleshoot this problem.
Reference:
courtesy of subford
Even with this method you can be led astray when using a Digital Voltmeter (DVM). The long length of wiring in the circuit can pick up induced voltage from other wires which will cause your DVM to read voltage when there really isn't.
The clue is your statement "I cut the inertia switch out and spliced the wires together. Right now, if I put a meter on the brown wire at the inertia switch without splicing it to the fuel pump wire, I get voltage when I turn the key on. If I splice it to the fuel pump wire and turn the key on, I get nothing." When you place a load on the circuit the "stray voltage" disappears. You more than likely have an open fuse or an open wire. Use a test light to confirm you really have voltage. Use the DVM for resistance checks.
The schematic on the right should be what you are looking for:
Reference:
courtesy of subford
Even with this method you can be led astray when using a Digital Voltmeter (DVM). The long length of wiring in the circuit can pick up induced voltage from other wires which will cause your DVM to read voltage when there really isn't.
The clue is your statement "I cut the inertia switch out and spliced the wires together. Right now, if I put a meter on the brown wire at the inertia switch without splicing it to the fuel pump wire, I get voltage when I turn the key on. If I splice it to the fuel pump wire and turn the key on, I get nothing." When you place a load on the circuit the "stray voltage" disappears. You more than likely have an open fuse or an open wire. Use a test light to confirm you really have voltage. Use the DVM for resistance checks.
The schematic on the right should be what you are looking for:
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shane733
Explorer, Sport Trac, Mountaineer & Aviator
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Apr 5, 2004 04:21 PM
