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  #1  
Old 05-10-2021, 02:20 PM
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e53 4.4 fuel pressure problem

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.
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  #2  
Old 05-10-2021, 02:31 PM
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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.
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Old 05-10-2021, 02:50 PM
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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?
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Old 05-10-2021, 03:22 PM
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curious about that, have a similar issue
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Old 05-10-2021, 03:25 PM
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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.
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Last edited by 80stech; 05-10-2021 at 04:22 PM. Reason: add
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Old 05-10-2021, 04:58 PM
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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.
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Old 05-10-2021, 05:08 PM
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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.
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Old 05-10-2021, 09:44 PM
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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.
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Old 05-11-2021, 03:56 PM
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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
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Old 05-11-2021, 05:29 PM
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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
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2006 Infiniti G35
2001 BMW 3.0I E53 X5 Build date 08/2000 SOLD
Lotus Europa 1970 Destroyed by fire
Lotus Europa 1970 S2 Renault Powered
Lotus Type 52 1970 Twincam Webers Powered
PORSCHE 911 Targa 1982 The Garage Queen
Audi Avant donated to Kars for Kids
BMW 525IT Sold
Audi 4000CS Quattro Sold
Jensen Healey Lotus Powered Sold
Opel 1900 Sold
Triumph Spitfire 1971 Sold
Triumph Spitfire 1968 Sold
Plymouth "Cuda" 340 Six pack SOLD
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