Green5pt0

Hi, I have a 92' 5.0 and it has a residual fuel pressure problem. I have a fuel pressure guage on my fuel rail and when I shut the car off the fuel pressure drops to zero within a few minutes. So, when I stop for gas, I shut the engine off and a vapor lock occurs. Then the car starts up very poorly and the idle surges badly for a few minutes.

I thought that the fuel injectors were leaking and allowing the pressure to drop. So I replaced them all with brand new FRPP 24# ones. That did not do the job, although it slowed the dropping fuel pressure, it does not drop as quickly now. Next I replaced the fuel pressure regulator with a brand new BBK adjustable unit. This did not stop the fuel pressure leak. I recently replaced the fuel pump also with a brand new unit, and the fuel pressure still drops to zero after a couple minutes of shutting the engine off.

Where could the fuel be leaking?? I know there's a fuel pump check valve but where is that?

Any info would be great this has got me stumped!

Thanks,

-Green5pt0

Green5pt0

I also wanted to add that I am still using the stock fuel rails.

FiveLiterRiceEater

how do the rails look? do you notice gas dripping anywhere on the engine or the ground?

whats your fuel pressure set at with your new regulatlor?

AdderMk2

we actually noticed this same issue with the "Notorious Notch" from Pro Mustang Performance

turned out to be a bad feed hose between the fuel pump and the sending unit.. had a leak in it

the reason your car is running poorly after the pressure drops is because you are overworking the pump to catch up with the demands of the car...

turn the key on and off a few times and you will "prime" the fuel system... this will alleviate your poor running issues from a start, however, i would recommend pulling the tank down again. check everything on the pressure side of the fuel system... anything after the FPR is not going to cause this problem

Green5pt0

No, there is no fuel leaking from the rails or anyplace else. The pressure is set at 40psi at WOT.

As far as over working the pump, and priming it by turning the key on and off a few times. That's not necessary becase one time of turning the key on brings the fuel pressure all the way up to running pressure without doing it more than once. So, when the engine is hot and I turn the key, the fuel pressure comes all the way up and I start the car and it runs really rough for a few mins.

AdderMk2

just turning the key once WILL NOT pressurize the entire fuel system.. if you are truly dropping to 0 pressure.

how is your guage hooked up? if you are not using one that threads directly onto the FPR or the rail itself... it may be lieing to you..

marx91

when a fuel pump is going bad it will lose pressure, just a thought

Green5pt0

The fuel pump is new its a 155lph pump. The guage is screwed into the fuel rail, and one turn of the key does prime the system right from zero. I've watched it happen many times.

Joel5.0

http://www.themustang-net.com/eec.shtml ....a leakdown of 5psi in 1-min is acceptable, you could rule out the AFPR (I've installed new ones, all brands, that allow more leakdown than the OEM) by pinching the return hose section and checking pressure...if it drops more than 5psi in a minute, the pump check valve (there are no external check valves)...or the hose connection AdderMk2 mentioned, could be the problem...BTST too.

Assuming your FP gauge is reading correctly, you have the system within specs to not have the idle problem at re-startup...reason for the KOEO/KOER self-tests....the leakdown problem though, will overload the pump and reduce its lifespan depending how big the leakdown problem gets...my 2ยข.

Green5pt0

OK, so if the pump is new where could the fuel be leaking from? I am losing alot more than 5psi per minute, and why does the car start so poorly when the engine is hot?