e53 4.4 fuel pressure problem

[candrade]

Hello everyone. new to the forum. i have a e53 4.4 year 2000 and it has a problem at cold starts. cranks long and then starts. no problem when hot.
i changed fuel pump, syphon pump doesnt leak and the syphon one way valve isn't stuck.
when the car is cold, i press on the relief valve on the fuel rail and doesn't have pressure. looses the pressure overnight.
what can be causing this? is this a fuel pressure regulator issue? should i change the fuel filter w/regulator?
thank you.

[80stech]

Other than an obvious leak, the problem could be the fuel pump, pressure regulator or injectors. Try cycling the the key to let the pump run for a bit before starting in the morning just to see if that helps before going further. A good fuel pressure gauge would probably help.

[candrade]

Thank you. I have checked and no leaks in the fuel lines.
Priming the pump several times in the morning helps start right away.
I would discard the pump as a culprit. I have tested 3 pumps.
How can i check for leaking injectors?

[Takimo]

curious about that, have a similar issue

[80stech]

Pull the injector rail out (don't disconnect the fuel supply) and watch for leaks at the injector tips or possibly even the injector body. Having a good fuel gauge (that reads properly and doesn't leak) can be a big help with this kind of thing.

Having replaced the pump 3 times doesn't rule that out as much as you would think.

[candrade]

Great, i will check the injectors as soon as i can.
How do i rule out the pressure regulator? Is there a way to test it?
I tried disconnecting the vacuum hose (the one that goes all the way to the fuel filter) from the intake boot but no change in idle. I also tried to blow onto it to see if theres a leak but nothing.

[80stech]

The vacuum line not having fuel in it only shows that the diaphragm is not ruptured, doesn't rule out not leaking down.
You really should get a good fuel pressure gauge before you go any further.

[upallnight]

Next time you start the engine have someone check the exhaust. If the injectors are leaking, they may create a rich enough condition that the exhaust will be BLACK. Since the engine starts when you prime the fuel pump and the engine rail doesn't show any pressure prior to the prime I would suspect leaky injectors or a faulty check valve at the fuel pump.

If you do pull the injectors, replace the o-ring in the intake manifold. If you don't you will be chasing air leaks from old o-rings.

[candrade]

Update. First i did upallnight test in the morning, no black smoke.
Then i lifted the injector rail, connected a 12v source directly to the fuel pump, no leaky injectors

[upallnight]

You can install an inline check valve that you can buy on Amazon.

https://www.amazon.com/gp/product/B0...b63dd592a4af2e

And follow this install procedure.

https://www.youtube.com/watch?v=6ezt4M1NZDk