Relieving fuel system pressure...
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Cargo Master
Joined: Jul 2009
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From: Des Moines
Relieving fuel system pressure...
For those of us who still have vac operated fuel pressure regulators, I was wondering if it was possible to relieve system pressure by applying vacuum to the FPR?
I was reading up on the FPR and if I'm understanding things correctly, the more manifold vacuum (higher RPM's) there is, the more the FPR lowers fuel pressure. If this is the case, could the fuel system pressure then be relieved by applying vacuum to the FPR with a hand pump?
Just curious. Looking for a way to make things a little easier in the future. IMO, it's easier to hook my vac pump to the FPR than it is to use my FP gauge on the shrader valve for relieving the pressure.
I was reading up on the FPR and if I'm understanding things correctly, the more manifold vacuum (higher RPM's) there is, the more the FPR lowers fuel pressure. If this is the case, could the fuel system pressure then be relieved by applying vacuum to the FPR with a hand pump?
Just curious. Looking for a way to make things a little easier in the future. IMO, it's easier to hook my vac pump to the FPR than it is to use my FP gauge on the shrader valve for relieving the pressure.
Fleet Owner
Joined: Aug 2005
Posts: 23,668
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From: Easton,Ks
No, at max vacuum you will only take it down to about 30psi on a V-8 and the pressure would be higher on a 4.9L.
Pull the fuel pressure relay on 1991 and older or fuse if it is a 1992 or newer and crank the engine.
Pull the fuel pressure relay on 1991 and older or fuse if it is a 1992 or newer and crank the engine.
Posting Guru
Joined: Apr 2011
Posts: 1,119
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From: Hartland, WI
^^ ditto. Vacuum actually decreases as the throttle is opened, so the FPR "closes" and fuel pressure increases. At idle there is more vacuum, the FPR "opens" and allows more fuel to return to the tank. Hence why fuel pressure increases when the vacuum line is removed when the engine is running.
New User
Joined: Aug 2013
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These are all great ideas. I have never really worried about relieving the fuel pressure, but then again I do end up smelling like gas. But When reading, my first thought was to depress the schrader valve on the injector rail, but that would still leave a lot of fuel in the lines.I was also thinking that vacuum is decreased upon acceleration.
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