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Matt, Engineer
Category: Ford
Satisfied Customers: 20360
Experience:  BEng hons Mech engineering, in auto industry 22 years
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98 Ford Expedition: the fuel pressure..psi..highway..fuel pump relay

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The same 98 Ford Expedition starts and the fuel pressure is around 36 psi, then it drops below 20 psi and shuts off. It does not do this all the time but enough times to leave me stranded on the highway. I replaced the fuel pump, swap the fuel pump relay with the horn relay. I have checked everything in that electrical circuit, the ECM relay, fuel pump fuse, fuel pump relay and the kill switch. I now have a check engine light on. The codes are 171 and 174. Look forward to hearing what you think.

Thank you & have a blessed day

Madison Jones

I'd try replacing the pressure regulator at the end of the fuel rail - this is straight mechanical component with no electrical connections as if faulty will cause fuel pressure to be incorrect
Customer: replied 5 years ago.
I forgot to say that I have pulled the vacuum line off the pressure regulator and the pressure goes up to close to 40 psi. I therefore assumed that the pressure regulator was working fine. I also sprayed some throttle body cleaner around the vacuum line to check for leaks and found none. If you still think it could be the vacuum regulator let me know. Note: It does not do it all the time.

Thank You & have a blessed day

Madison Jones

In that case the regulator sounds fine so I'd try replacing the fuel pump filter it should be a black canister in fuel line under drivers side mounted to the frame - the bottom unscrews to reveal a filter cartridge
Customer: replied 5 years ago.

I'm sorry Matt, I should have told you that I changed the fuel filter before replacing the fuel pump. That does not mean that it is not bad, I had to replace the fuel pump twice. The first fuel pump went dead, it would not do anything with 12Volts applied to it.


I don't believe in luck, just blessings, but thank you for your thoughts toward me.



Thank You & have a blessed day


Madison Jones

Hello Madison

at least we're thinking along the same lines....

Well as you've got a a new pump , new filter and you're confident that you've got 12V at teh pump at all times then this leaves a possible problem with the pickup inside the tank

if this has come loose or is choked with debris then this can give issues as the pump will be starved of fuel so it may be worth withdrawing the sender / pickup unit and inspecting it.

One other thing to try as a test is to run a new wire from the battery to the pump so it runs all the time - this eliminates any wiring issues to confirm if the problem is mechanical or electrical

Edited by 350Matt on 1/7/2011 at 7:36 AM EST
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