what are all the simptums you are having?

Well it started with no power after mid throttle to the floor. I have replaced all the small stuff, filters and even the fuel regulator on the pump but still no change. With a Tech II connected driving it will drop from 15k psi to 3k and then when I let off the throttle it will jump back up to about 15k and then down to desired.

first I would check and see if you have a fuel line colapsing in or out of the fuel filter. If you have a way to check fuel pres. check the actual with the engine off it should read 1.1 to 1.8 mpa, if not your pres. sensor could be bad. I have an lly and am not sure how the lb7 are set up but if you take the line off between the fuel rail and the return, plug the return side and start the truck if you have fuel coming out the fprv it is sticking open. and for the regulator there should be a way to go in with the tech II and graph out what the desired is and what the actual is.

I have been told that when the pump starts going bad it just GOES, and the symptoms that I am having are not for sure the pump. So I am trying to get help with the trouble shooting of the FPRV. The leak earlier sort of confused me. I think the FPRV is on the backend of the rail on the drivers side but the lics show that it is located above the CP3 area just to the right side of center.?.?.?

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Yes I have checked the hoses from the filter. Used a vacume gauge to test this. All checks good on the input to the pump. Can a pump just drop from 15k to 3k and always at the same pressure?

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It really seems that the FRPV could be popping off at 15k or so and causing this...???

what year is your truck

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I have an o5 lly and the fprv is at the back of the ds rail there is a rubber hose going from the fuel rail to the return line if you pull the rubber hose of the fuel rail and plug it so you dont loose fuel from the return. then put another hose on the fuel rail run that into a pop bottle or somthing. Start the truck and if you get any fuel in the pop bottle the fprv is not sealing up. the fprv should not open until just 23000 psi.

Okay, at the end of the fuel rail the FPRV has a metal line connected to it and it comes back up to something that has several lines connected to it. There is a Banjo bolt that this metal line goes to and there is a rubber hose there. Is that where I can plug the return and put a hose in a bottle?

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oh it is a 2003 3500 dually

so the metal lines comes up to a distribution block and bolts to it and then there are rubber lines that also come into it correct

I think I may have been confused on what I was looking at. There is nothing other than a metal line running from the backend of the fuel rail. It runs back up to the middle of the motor up just above the CP3 area. I think I can see the pop off valve (FPRV) on left end of something? what is it screwed into?

The lb7's dont have that kinds of set up, thier fprv is located on the end of the junction block in the valley of the engine



The metal line is part of the supply for the injectors it coes from the juntion block to the fuel rail.

the little line with the banjo bolt is the fuel return line and thee return fuel from the cp3, injectors, fprv all share that same line.

to tell you the truth I am not sure what exactly it should look like on an lb7
Is there any way to take a picture of it