Fuel Pressure Issues

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Apr 19, 2025 | 02:38 PM

Ritt

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Fuel Pressure Issues

Hi, I have a 1994 f150 5.8L that I’m having fuel pressure issues with. When turning key on/off pressure is good and gets up to about 40PSI when I start the truck it drops to about 25PSI. I have been told that normal fuel pressure should be between 30-45PSI at idle. When I pull vacuum line off of regulator the pressure only goes up to 35PSI. I have replaced the fuel pump for the second time this year and it does the same thing. The regulator was replaced with the 1st pump. Also have a new filter on it. I’m wondering if I have a possible issue with the regulator or if it is something else. Thanks

Apr 19, 2025 | 02:54 PM

Conanski

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From: Ottawa, Ontario

Normal running fuel pressure is 32-35psi at idle and 40-45psi with vacuum disconnected from the regulator.
Does fuel pressure hold after the engine is shut off or does it drop immediately? If it drops what does the engine oil small like... any hint of gas?
Is this a dual tank truck or single?

Apr 19, 2025 | 03:12 PM

Ritt

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This is a single tank truck. When shut off the fuel pressure drops a little bit immediately and then holds at about 20PSI. There is no signs of fuel getting into the oil. Thanks

Apr 19, 2025 | 10:45 PM

Conanski

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Joined: Jun 2006

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From: Ottawa, Ontario

Sounds like the pressure regulator is faulty, but you might double check pressure with a different gauge just as a last step.

p.s. One other thought, can you verify you have full battery voltage at the pump? Low voltage from bad grounds or corroded connectors anywhere in the electrical system are fairly common in older vehicles like this.

Apr 19, 2025 | 11:59 PM

Ritt

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Ok thank you I’ll check voltage I have checked pressure with both a harbor freight gauge and a snap on and it is the same

Apr 20, 2025 | 09:31 AM

1Butcher

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How do you know your fuel pressure tester is good? When everything starts to look like crap, many times it's your test equipment. This really applies to Fluke DVOMs.

Apr 20, 2025 | 10:27 AM

Ritt

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I know the tester is accurate I checked with 2 separate ones one was a Maddox and one was snap on

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Apr 21, 2025 | 11:09 AM

1Butcher

Cargo Master

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New does not mean good. It's not the first time I have read that installing a new part was not good. I've been there myself. That is why testing with good tools proves if the new part is any good.