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post #1 of (permalink) Old 01-11-2006, 04:17 PM Thread Starter
 
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Fuel pressure drops to 0 psi when shut down.

Hey guys,
Just need alittle help here. I installed one of those permanent mechanical fuel pressure gauges that the mustang guys use on the fuel/injector rail, and I noticed when I shut the truck down the pressure instantly drops to 0 psi. Before it starts, when I turn the key the pressure jumps to 40 psi. Any ideas what it could be. The truck runs great though.......It did this w/ either tank selected.
My truck has dual tanks w/ the 2 high pressure in-tank pumps. 1991 F-250 w/ 5.0L

Thanks,
Jerry D.
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post #2 of (permalink) Old 01-12-2006, 01:19 PM
 
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Re: Fuel pressure drops to 0 psi when shut down.

when you turn the key, it triggers your fuel pump. fuel pump runs, pressure in the line is created. shut it off and pressure in the line disappears because is pumps are no longer working.
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post #3 of (permalink) Old 01-12-2006, 07:59 PM
 
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Re: Fuel pressure drops to 0 psi when shut down.

Pressure should stay on fuel rail at least overnight. Mine is still at 20psi on the 3rd day of no use.
The three items that keep fuel pressure are injectors, fuel pressure regulator, and fuel pumps. Other than those items, a leaky line, leaky fuel pressure gauge, or injector seal would need to be present. See that the seal on the new gauge doesn't leak. The 2 gauges that I have had each required removal of the schrader valve first.
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post #4 of (permalink) Old 01-14-2006, 12:24 PM
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Re: Fuel pressure drops to 0 psi when shut down.

A leak wouldn't cause the pressure to drop "instantly" - if it was that bad, the truck would run out of gas in moments, and there'd be no pressure for the injectors.

It has to be the check valve in the FDM sticking open. Try some fuel additive to lube it up (maybe MMO or Techron?), but I suspect you'll have to change the FDM if you care enough to fix it. I wouldn't worry about it until it causes a problem.

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post #5 of (permalink) Old 01-19-2006, 12:18 AM Thread Starter
 
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Re: Fuel pressure drops to 0 psi when shut down.

Thanks for the replies guys. I went ahead and removed the FPR and one of the O rings was broken. I ordered a rebuild kit for the Mallory FPR. I hope this is the prob. I'll keep you posted.
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post #6 of (permalink) Old 01-19-2006, 12:17 PM Thread Starter
 
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Re: Fuel pressure drops to 0 psi when shut down.

Update:

All is well..........I installed the rebuild kit for the FPR. and it worked.
It's holdin 42 psi as we speak.
I gotta alittle scared when I first started it up. The fuel pressure gauge was reading 80 psi! I cranked it down REAL quick!
Good to go! Thanks for all the helps guys.
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