Confused on my fuel pressure

[lilredex97]

I have a 1999 4.0 ohv. After a couple of cylces the fuel pressure goes to 60 and stay there for a few minutes. I cranked it up and idling it stays at 60. I let it run for about 15 minutes and shut if off. Then the pressure drops to about 40. Cranked it back up goes to 60. but it wont hold there it goes to around 40. My pressure gauge is not leaking so the pressure has to have gone somewhere? And why didnt the pressure drop on the first test? Very confused on it

 

[my98nnj]

Are you having a drive-ability issue or engine problem or are you just looking at FP?
More detail on what/why your looking at FP might help.

 

[lilredex97]

The issues is lack of power on hills and such and hesitation till you get to about 40. only code it has is the after cat o2 sensor. the cat is about 1 year old. had recent tune up by the PO. the past codes was for precat o2 sensors reading lean. replace sensors and code went away. then had a code camshaft position sensor i replaced that and the code went away. I dont believe the driveabilty problems is sensor related thats why i checked FP

 

[imp]

Leaky pressure relief valve at the pump, in the tank. imp

 

[JusTheUsual]

install a new fuel pump.

 

[lilredex97]

Thank ya'll for your feedback. I will replace it.

 

[PaulKDM]

Thank ya'll for your feedback. I will replace it.

Did you replace it yet and did that solve your problem? Just curious because my FP drops to around 20 or so after a few minutes after I turn the engine off and I am trying to trouble shoot a P0171 code.

Thanks,
Paul

 

[JusTheUsual]

Did you replace it yet and did that solve your problem? Just curious because my FP drops to around 20 or so after a few minutes after I turn the engine off and I am trying to trouble shoot a P0171 code.

Thanks,
Paul

That could be your fuel pressure regulator. That keeps your fuel pressure up, along with other things. Yet that also could be a part on your fuel pump also

 

[SoNic67]

Actually the likely culprit is the check valve in the pump assembly.
It normally prevents the pressurized fuel to leak back into tank.
A new pump, as suggested, is best. With a new sock filter,

 

[PaulKDM]

Actually the likely culprit is the check valve in the pump assembly.
It normally prevents the pressurized fuel to leak back into tank.
A new pump, as suggested, is best. With a new sock filter,

Thank you for the info. I will check into replacing it. There are a few people that have told me that the FP will drop after turning engine and power off but I'm not convinced that it should. Just a thought. I am also experienceing an initial spike in RPM on a cold start, up to 2,200 - 2,300 RPM's. I have read a few threads on here saying that is normal but it hasn't started doing that until a few months ago and that can't be normal. This vehicle only has 118k miles on it. Hopefully it's all related. Later this evening I plan on hooking up FB guage, turn key off and on ~ 4 times to build up pressure to ~66 PSI and see if I get the RPM spike. Thanks again.

Paul