Fuel Pressure Not Keeping
- Thread starter BrokenPony
- Start date
I'm in the same boat as y'all. Brand new 255lph and new holley adj FPR. I'm thinking mine might be related to my FPR since it didn't hold vacuum but who knows. Summit is sending me the return box and I'll ship mine off asap so I get the next "new" one. Subscribe to my thread underneath this one and I'll post my results there.
Does the system maintain pressure when running?
It's actually pretty common and I believe the fuel pump is the culprit. Not quite convinced it's an actual problem though. Mine bleeds off slowly after stopping the pump. 5 mins and it's at 0
It's actually pretty common and I believe the fuel pump is the culprit. Not quite convinced it's an actual problem though. Mine bleeds off slowly after stopping the pump. 5 mins and it's at 0
Aftermarket FPRs generally drop pressure quicker than OEM FPRs.
As said, as long as pressure is adequate while running, it's no biggie. You don't want pressurized fuel in the lines when the car isn't running anyhow.
As said, as long as pressure is adequate while running, it's no biggie. You don't want pressurized fuel in the lines when the car isn't running anyhow.
After some more though, now I understand why the line is supposed to retain pressure after shutdown. It prevents vapor lock and hard starting on a hot engine.
Here’s why: when you pressurize a liquid, you raise the boiling point. It doesn’t matter what the liquid is water, oil, gasoline, brake fluid. That’s why your car has a pressurized radiator: instead of water boiling at 212 F, with 14-15 PSI pressure, it boils at 250 F. Gasoline pressurized to 40 PSI would react similarly, and its boiling point would go up beyond the 180F-220F commonly found in engine compartments.
A fuel supply line full of nothing but vapor would make the car hard to start until the vapor bled off during cranking, or the pressure inside the fuel supply line forced the vapor to condense back to a liquid.
Here’s why: when you pressurize a liquid, you raise the boiling point. It doesn’t matter what the liquid is water, oil, gasoline, brake fluid. That’s why your car has a pressurized radiator: instead of water boiling at 212 F, with 14-15 PSI pressure, it boils at 250 F. Gasoline pressurized to 40 PSI would react similarly, and its boiling point would go up beyond the 180F-220F commonly found in engine compartments.
A fuel supply line full of nothing but vapor would make the car hard to start until the vapor bled off during cranking, or the pressure inside the fuel supply line forced the vapor to condense back to a liquid.
Alright! jrichker now give us a write up on the process of diagnosing the fuel system
I already have four tech notes on troubleshooting the electrical part of the fuel system . One for 86, another for 87-90, another for 91-93 and one for the 94-95 Mustangs. I guess the next project will be to do a tech note on the fuel plumbing/pump and regulator troubleshooting.
I have an occasional hiccup with my current 5.0 that seems to be common to the previous 89 GT I had. I have heard that others have had the same experience. The fuel system mysteriously quits working and I am stranded until it starts working again. The fix seems to be to bang on the fuel pump relay. Troubleshooting in a hot parking lot when you in a hurry has given me a new appreciation of the difficulty of diagnosing the circuit. I am seriously thinking of building a plug in relay circuit tester using an old relay housing, a relay socket and 4 LEDS to show the state of the voltages on the relay pins.
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