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Fuel Pump Question

 
Old 02-03-2019, 10:10 AM
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Default Fuel Pump Question

My 88 F150 has two fuel pumps. How likely is it that both would fail at the same time? When I turn on the key I hear the fuel pump relay click, but that's all. I don't hear any pump sound. There's no fuel pressure at the rail. The truck hasn't been driven in a year. Could old fuel have caused both pumps to fail?

Do both fuel pumps make a sound, or just the one in the tank? I'm pretty sure the low pressure pump in the tank is not working. Could the high pressure pump be running and not making a sound if it's not getting fuel?

I measure 12 volts at the high pressure pump. I haven't checked at the tank because the connector is not accessible unless I lower the tank.
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Old 02-03-2019, 12:59 PM
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Originally Posted by forum View Post
My 88 F150 has two fuel pumps.
Are you saying it only has 1 tank? It will be easier for us to help you if ALL the truck's details are in your signature as this caption explains:


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Originally Posted by forum View Post
How likely is it that both would fail at the same time?
Not very, but it IS common for the truck to keep running when the low-pressure pump fails, and then stall when the HP pump finally quits.
Originally Posted by forum View Post
There's no fuel pressure at the rail.
Did you check with a gauge? Did you try tripping & resetting the inertia switch?


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The truck hasn't been driven in a year. Could old fuel have caused both pumps to fail?
Fuel doesn't go bad in a year - it takes about 5. And it takes even longer for it to go SO bad that the pumps can't move.
Originally Posted by forum View Post
Do both fuel pumps make a sound...?
Yes.
Originally Posted by forum View Post
Could the high pressure pump be running and not making a sound if it's not getting fuel?
No.
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I measure 12 volts at the high pressure pump.
Exactly where? That first caption contains a link that explains how to embed pictures in your posts.
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I haven't checked at the tank because the connector is not accessible...
Then use stickpins as pierce probes in the wires.


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Old 02-03-2019, 09:46 PM
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Steve.

Thank you for the detailed response. You obviously put a lot of time and thought into it. Really appreciate!

My truck has one fuel tank. It's a 1988 F150 302v8 auto. Maybe I can get a photo of the spec sticker later. The truck is not here at my house.

I checked fuel pressure at the fuel injector supply rail (schrader(?) valve) with a gauge.

I checked high pressure pump voltage at the pump connector. I unplugged the connector and attached volt meter to two pins inside the harness connector.

To test the pumps I grounded the fuel pump test pin on the VIP(?) connector. The fp relay clicks and the volt meter shows 12V at the high press pump connector.

It's going to take me a little while to go through all the valuable info in your response.

Thanks again!
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Old 02-03-2019, 10:08 PM
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A pic of the VC label isn't useful - YOU putting all its information into your signature is.

Follow the HP pump wiring down to the pump body, slide the rubber boots up, and inspect the terminals there. Make sure they're tight & not overheated. Check voltage there, with everything connected normally, and the DLC (VIP) jumpered:


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