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Old 09-17-2010, 07:27   #1 (permalink)
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2004 5.4 Expedition Fuel pressure problems

I have read many blogs about the fuel pressure problems on Expeditions but I'm still not sure if I have a problem with the
  • Fuel pump
  • The sending unit (control module)
  • Fuel pump relay
  • Or with the fuel pressure regulator
I replaced the fuel filter but problem continued.

In testing the fuel pressure I took the following procedures

  1. Connected a fuel pressure gauge to the shredder valve on the fuel rails.
  2. I relieved the pressure from the fuel rails with the gauge i was using.
  3. With zero pressure on the gauge I then turned the key to the Run position (position before cranking)
These were my results:
  • The pressure when up to about 10 psi on the first time we switched key to run.
  • When the pressure began to fall (after 3 seconds) we turned key to off and then run again, it would jump another 13 psi or so.
  • Now the combined psi from 1st and 2nd time were up to about 23 psi. We turned it off again and back to run and another increase of 16 psi. Now there is about 39 psi. We this this 5 times before we got a combined pressure of about 55 psi which is right around where the pressure should be.
  • We then cranked the engine and it started fine because obviously there was enough pressure in the lines but it took cycling on and off 5 times before we got the pressure up to the required.
  • When we turned off the engine the pressure dropped from 55 to about 5 psi in a matter of 5-7 seconds.
  • Once it was at 5 psi, we tried cranking it and wouldn't start unless we cranked it a second time (or we cycled the key on and off 3-5 times)

From my testing what would you conclude. What is at fault? Is it my relay, fuel pump, fuel pressure regulator, or sending unit?

Thanks a lot for your help
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Old 09-22-2010, 06:49   #2 (permalink)
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Re: 2004 5.4 Expedition Fuel pressure problems

Will it hold 50 psi while the motor is running? If not it's probably the fuel pump or the filter sock on the inlet of the fuel pump is clogged. Since the pump eventually gets the pressure up to 50+ psi I'm thinking the filter sock is partially clogged, blocking the pump inlet. If you remove the vacuum tube from the regulator you will get full pressure to the injector manifold. But if the motor is not running during your tests there should be no vacuum anyway. If the motor has a hard time idling and you remove the regulator vacuum line and this improves the idle quality then your fuel pump is either shot or blocked flow.


- Mike
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