Engine/Transmission (1998.5 - 2002) Funny (not ha-ha) drop in FP

[jsnyder]

Here's the scoop. I replaced the original lift pump at 81k miles. New pump was putting out textbook pressures. The FP at idle dropped about 1. 5PSI, so I changed the fuel filter and life was rosy again.



Now about 2k miles later, when I really hammer the throttle my FP will drop sharply, but then begin to climb back up. For example, towing my horse trailer if I really pour the coal to it on a hill, the FP will drop to about 6-7PSI, and then climb back up to about 10PSI.



Any thoughts as to what's going on here?



The truck is bone stock, running winter blend #2 with Power Service additive.



TIA.



JS

 

[Double J]

If your running an electric gauge the first thing I would check is the sending unit.



Hook up a mechanical and see if it's doing the same thing.



Clean LP connection with some electrical spray cleaner and slap some di-electric grease on it.



Any fuel leaks?



I think you know where this is going so, happy LP shopping.

 

[jsnyder]

The fuel gauge is a Westach. I will be replacing the sending unit (it's three years old) as a cheap try.



An interesting update though. Yesterday I towed the horse trailer and three horses (about 8500 lbs) to the mountains. I noticed that the pressure does NOT do funny things with the trailer, even when I am WOT up a 6% grade.



It only does it when I push the pedal through the floor empty. Is it possible that something is getting restricted by the sudden demand for fuel?



I know the lift pump is an easy culprit, but I'm not convinced it's that.



Edit: the cruising pressures with the trailer were 11-12 PSI, 10 PSI pulling hills, 14 PSI idle.

 

[jjordan1]

My pressure has never been better than 8 psi. I talked w\Cummins & they said as long as i have possitive pressure not to worry. I have 56000 on my 2001 2500. Pull a 30` fifth wheel . BUT i still worry.

 

[RustyJC]

My pressure has never been better than 8 psi. I talked w\Cummins & they said as long as i have possitive pressure not to worry.

If Cummins is willing to pay for the new VP-44, they're right, don't worry! Otherwise, invest in a new lift pump if you're sure your gauge is accurate.



(Still on original lift pump. 16+ PSIG idle, 14-15 PSIG cruise, 11-12 PSIG WOT towing 5th wheel - see signature. )



Rusty