Engine/Transmission (1998.5 - 2002) lfit pump installed not what is wrong

[Pigpen]

I installed my new lift pump last night. I checked the pressure with my Isspro gauge in the truck and it is reading 12psi. I was under the impression that is was supposed to be 14psi. Does anyone have any suggestions?



Thanks

Jake

 

[Truckie]

Its hard to say what these things should be at, but most should be around 13 to 15 psi at idle. how old is your fuel filter? Pop a new one in and see if it brings up the pressure, may just be a clogged filter.

I'm on my 3rd lift pump with in a year. The original on the truck went at 19,000 was replaced at the dealer, and that one was on the truck for five days,went bad, bought a new one from Cummins and I just replaced it this Sunday, with 29,000 on the truck, replaced it with one a friend gave me and now have FASS on order.

MIKE

 

[dresslered]

It is probably working within their loose range of specs. I installed my third one two weeks ago and it idles around 14 but I can pull it down to 6-1/2 psi if I try. The one that I replaced was experiencing intermittant fluctuations but I could never pull it down below 9-psi. They all seem a little different.

 

[Tcolesanti]

I put a new lift pump on 3 or 4 months ago that I bought from the local cummins dealer. Strong 15psi at idle and I can barely pull it down to 10. 5psi, even with the VA box.

 

[johnrv4]

Is there a part number on the box the pump came in? There have been 5 revisions (I believe) on the lift pump. I think the current number is 3990105. Maybe you got one that isn't the current revision? Just a thought...

 

[B.G. Smith]

The lift pump in the 99 should put out a minimum pressure of 10psi with engine running and 7psi in start mode. The relief valve in the vp44 opens at 14psi. bg

 

[Pigpen]

I wonder if it is the gauge. When I installed it, I bled the line some. But I wonder if it still has air in it?

 

[dresslered]

When I installed it, I bled the line some. But I wonder if it still has air in it?

Air won't hurt the readings. In fact, it is probably smart to leave air in the line for additional dampening for the sensor--whether it stays in there is another question.



If you are really in doubt about your gauge, borrow someone's mechanical for a quick comparison. I tend to think that what you are reading is accurate.

 

[ntillm01]

Sounds like the lift pump is ok. As stated in another post, there is a pressure relief valve that iis part of the system also. It may be a little weak and opening at 12 psi instead of 14. Also mentioned, a clogged filter could be the problem also.

 

[Pigpen]

I just changed the fuel filter a week ago. It does seem like it will not go above 12, like is just stops right there. Is there a way to fix the relief valve?