Fuel delivery issue
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Junior User
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From: Socal
Fuel delivery issue
I own a 1985 f250 with a 460. My truck has a fuel delivery issue. I was driving home today and the truck suddenly died . I tried to start it again but it would just turn over . So I energized the fuel pump relay with a wire connect to the battery. I could hear the fuel flowing . So I disconnected it and the truck fired back up and made it home no problem. It has done this before and I always energize the relay and it fires back up. I have noticed as time passes the truck takes a longer time cranking before it starts . And that's when the truck dies . So I don't know if it's the pump or relay . I was thinking of just running an external fuel pump
Lead Driver
Joined: Nov 2013
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Wiring diagrams here:
Electric Fuel Pump Control - ???Gary's Garagemahal
How is the oil pressure? If low, the oil pressure switch is doing its job and shutting off the fuel supply as designed.
If the oil pressure is okay, your oil pressure switch is probably borderline inaccurate and breaking the circuit too soon.
By chance did this happen after maybe 30 seconds at low RPM with the engine fully warm? A hot idle is when oil pressure is lowest, and then you've got about half a minute for the float chamber to run dry.
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Junior User
Joined: Oct 2015
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From: Socal
Sounds like a bad input to the relay, since everything seems to work when you bypass that portion of the control circuit.
Wiring diagrams here:
Electric Fuel Pump Control - ???Gary's Garagemahal
How is the oil pressure? If low, the oil pressure switch is doing its job and shutting off the fuel supply as designed.
If the oil pressure is okay, your oil pressure switch is probably borderline inaccurate and breaking the circuit too soon.
By chance did this happen after maybe 30 seconds at low RPM with the engine fully warm? A hot idle is when oil pressure is lowest, and then you've got about half a minute for the float chamber to run dry.
Wiring diagrams here:
Electric Fuel Pump Control - ???Gary's Garagemahal
How is the oil pressure? If low, the oil pressure switch is doing its job and shutting off the fuel supply as designed.
If the oil pressure is okay, your oil pressure switch is probably borderline inaccurate and breaking the circuit too soon.
By chance did this happen after maybe 30 seconds at low RPM with the engine fully warm? A hot idle is when oil pressure is lowest, and then you've got about half a minute for the float chamber to run dry.
Lead Driver
Joined: Nov 2013
Posts: 7,174
Likes: 1,174
Call me Mr. Vegas, but given the chance to spend your money, I'd gamble on a new oil pressure safety switch and see what happens. Check the connector, too, as mentioned in post #2.
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Junior User
Joined: Oct 2015
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From: Socal
well I hope it fixes it. Because I really don't know what is causing this , it's weird
Lead Driver
Joined: Nov 2013
Posts: 7,174
Likes: 1,174
Well, look at the wiring diagram as linked in post #3. See page 102 for single tank, or page 105 for dual tanks. You said you had energized the relay, which is wired the same in both diagrams.
Did you apply power where wire 640 R/Y connects to the relay? If so, you had bypassed the oil pressure safety switch, so that's the circuit to investigate. The first best guess is to check the wiring and connector, followed by replacing the switch. Fingers crossed.
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