Losing fuel pressure

[prgt347]

For list of mods, please see garage.
Been trying to get the car to start for months and have eliminated just about every possibility that's out there. One thing that I can't seem to find an answer for is why I'm losing fuel pressure. Key on (no crank) cycles the fuel pump to 40 psi then drops to about 20 after the pump turns off. Then within 30 seconds will be down to 0 psi. Cranking the car keeps the pressure between 36-40 psi but as soon as I stop cranking it drops immediately to 20 psi then down to 0 psi within 30 seconds.

I've never seen this before and can't seem to get any good answers for why. Talked to Aeromotive about the regulator but from what the tech said mine is checking out fine. I've also heard it could be something in the fuel pump. I don't have any leaks in the fuel lines as I've checked from engine to pump and no issues. Just can't seem to hold pressure.

A lot more to the story and most of it is on this site in other posts. But I have a feeling that whatever the deal is with the pressure, that is a major reason for the car not starting. When it does start, and every now and then it will, it runs perfect and pressure is steady. But as soon as it is turned off it won't start again...sometimes for days, months, etc.

I've heard there is a check valve in the fuel pump. Any truth to this? I have a spare pump and have considered swapping out but don't want to go through the hassle if there is no reason to do it. Any advice is appreciated. And yes, I've gone through Jrichter's no start checklist and so far everything is checking out...

 

[Mustang5L5]

Mine behaves this way...and runs perfectly fine. Crank key, bit don't start, it pegs to 40, drops to 0 within maybe 10-15 seconds. With engine running, holds 40 psi all day long. Engine runs fine and it's been like this for 10 years maybe. At wot, it's able to easily maintaine 40 psi.

 

[larrym1961]

Mine behaves this way...and runs perfectly fine. Crank key, bit don't start, it pegs to 40, drops to 0 within maybe 10-15 seconds. With engine running, holds 40 psi all day long. Engine runs fine and it's been like this for 10 years maybe. At wot, it's able to easily maintaine 40 psi.

MY fuel pressure does the exact same thing, and this with a new fuel pump, injectors, regulator and rubber check valve @ the return line in the fuel pump assy. Holds pressure just fine while running. The only thing is @ a cold start I may have to start a couple times to get it running, but once warm starts first time, every time.

I have read that some aftermarket fuel pressure regulators can cause a hard start condition. This problem never happened until I switched from a Kirban to a BBK fuel pressure regulator.

 

[Mustang5L5]

I run a Kirban here. Always starts first crank.

If I remember correctly, the stock reg did hold pressure for a while. Would take a day to bleed down.

 

[twfs]

As stupid as this sounds I had a similiar problem a while back. I would check my fuel pressure and it would be different every time. Come to find out when i put my new injectors in I didn't have a fueline goining the fuelrail connected all the way. Did not leak any gas but got to playing around with it and pushed on one and heard it actually click and lock in to place after that fp stays where i sat it at. Hope this helps