Engine/Transmission (1998.5 - 2002) Can a Lift Pump Do This?

[rblomquist]

Can a lift pump work while the engine is running but not work (run) by just bumping the ignition?



In other words is it possible for a LP to pump fine (show pressure) going down the road but when the bump test is tried it not work?

 

[JR2]

I would guess anything is possible. The ECM only send half voltage to the lift pump when you are starting so maybe the lift pump is not running with 6 volts, but does fine with 12. Maybe check the connection to it to be sure it not full of crud.

 

[Dane]

Same as you, mine does not show pressure until the engine is running. Don't know why...

 

[jkern]

i have my PE 4200 wire with the stock harness, and it runs full speed all the time. it runs before i start, while i start and all the time while running.

 

[Beast2B]

with a mechanical gauge I can see the LP pressure jump for a half second or so when I bump it, but goes to zero until started.

 

[Rammin]

rblomquist



you have the same tuck I have with the westec FP guage. when I turn the key to start ,the pump runs for about 2sec. the guage shows fuel pressure usually up to 12 lbs. before pump shuts off. Then when truck is started pressure comes right up. you may want to check your ground. or could be a sending unit problem

 

[Tcolesanti]

Mine jumps up to about 9-10psi then the lift pump stops and the pressure bleeds off. Then once it starts, the fuel pressure comes right up. Auto meter gauge.

 

[rweis]

I have Westach's and they do the key on, bump to about 12 psi for 1 second, then to zero, then start engine, fp is right there as the engine starts.



Bob Weis

 

[rblomquist]

Guys, I have a mechanical test guage with me at all times. I verified with it and I'm only 2 psi different between the electrical and mechanical which tells me the electrical sender is about spot-on because the open port I have to connect my mechanical test set is on the pre-filter side (you gotta love the 98&99's filter housing setup for this stuff).



Most of the time it's reacting just like you guys are explaining however, last night when I bumped the key the LP ran for the 20 something seconds it's supposed to and my electrical gauge read pressure the entire time. Guess I'll be keeping a closer eye on this behavior.