so how do i know what part of the fuel system it is?
start with a fuel pressure and leak down test.
Fuel Pressure test
1) if pressure is low
a. check fuel pressure regulator
b. check fuel pump
2) if pressure is high (this is not your problem)
a. check FPR
Leak Down Test
1) truck is holding pressure after pump turns off
a. then I would check fuel injectors or start looking toward electronics
2) Truck looses pressure rapidly when FP is not running
a. check for a leaky fuel injector (you would probably notice fuel in your oil)
b. check/replace the one way valve (this is my bet)
c. Check for leaks in the fuel system (you should be able to smell something though)
to perform both of these tests you need to get a fuel pressure gauge available at your local parts store. Make sure it is the one that attach's right to the shrader valve.
Then do the following
1) make sure the engine is cool
2) attach gauge to the shrader valve on the fuel rail, be careful there could be some pressure in the line.
3) turn the ignition key on and start the truck and note what pressure the gauge climbs to, it should be right around your vehicles normal PSI
4) then turn the truck off and watch the gauge
5) the truck should hold that pressure for a few minutes, and should very slowly leak down (that is normal) over the course of 15 or so minutes, eventually stopping at a lower pressure but not going to 0.
6) if the pressure goes down quickly to 0 then you have a problem, more than likely the fuel is being siphoned out of the fuel rail and back into the tank.
anyway give that a try and let us know what happens
