rjrkihap

I’ve been following the fuel pressure threads (as I too have recently lost my vp44 and lift pump) and am a bit confused. Cummins and Dodge (Bosch also) state that as long as your lift pump is putting out 5psi your vp44 is just fine. In fact, they will not warranty the pump until THEY can verify less than 5psi. However, I have also read that as soon as you drop under 10psi your vp44 is in danger of being damaged. I’ve also read that those who have had the in-tank lift pump retrofit are seeing pressures under 10 right after the install with Dodge commenting that flow is what’s important and not pressure.

My question is who’s right? If the under 10psi rule is correct, then a lot of us will end up replacing our lift pumps ourselves even if it’s still under warranty.

Thanks

Ron

Clunk

I think everyone has their breaking point, mine was <7 psi Wide Open Throttle (WOT), then I installed a replacement and located it to the frame rail in front of the fuel tank. A lift pump fuel pressure gauge is required to know what your WOT fuel pressure is.

torquefan

There doesn't seem to be a definitive answer here. I work on a lot of these trucks. Sometimes you will see a truck come in with a dead VP44 and the lift pump will be dead or weak as well. I've also replaced many dead lift pumps that have been run that way for months, and their VP44's are still fine. My logic works like this: the more fuel pressure the better. If the LP still maintains a positive pressure at WOT under full load, it's doing its job. I don't think there's anything to gain by replacing it every 3 months, but if you have a pressure gauge, and can monitor a gradual dropoff, you can tell when it's time to replace.

engcogod

I have read alot that anything over 18 - 20psi can actually hurt the insides of your VP44. Your VP will be happy as long as it has a good consitent flow & pressure...

pmtg

dont know how they test, i believe its a volume test which roughly correlates to 5psi of fuel pressure. i also dont believe they test it under load, just turn the key and see what it pumps out. they need to test at WOT with a load on the motor.

flow is a result of pressure. pressure determines (among others things) the velocity of the fluid, more pressure (provided other things remain the same) more velocity, which equates to more flow.

the lift pump provides fuel to the VP for use in combustion as well as cooling the VP and returning to the tank. is failure due to mechanical damage of the VP during low fuel pressure or is failure due to heat buildup that damages the electronics of the VP during low fuel pressure? probably would depend on the circumstance. just thinking out loud on this one...

rjrkihap

So basically, as long as I have possitive pressure at WOT (say 5 to 70 then things should be OK. Anything below 5psi and it's time to replace the lift pump.

After replacing the LP and VP44 I installed an electric gauge pre filter and a mechanical gauge post filter. The lift pump was dead within a month and replaced under warranty (at Cummins NW). Assuming that a person doesn't have a bad LP right out of the box (like I had), can a person anticipate several years from a LP? Also, when a LP begins to go bad, do they normally do so over time (months) or is it pretty quick?

Thanks for the help.

Ron

Clunk

My stock pump was kinda grungy so it was likely original. It was over 3 years old when I replaced it. I'd say not running out of fuel, good filters & fuel treatment helps your lift pump live.