Engine/Transmission (1998.5 - 2002) Lift Pump Pressure Decreasing Over Time......How Low Is Too Low???

[Chief USA]

I put a guage on the injector pump schraeder valve and check lift pump pressure at each oil change and fuel filter change. I changed my fuel filter today and ran my pressure check. I get 10 psi at idle and 6 psi lowest observed at WOT on a 5th hard pull. When I first got the guage year before last; the lift pump idle pressure was 15 psi and WOT minimum pressure was 8 psi.

I figure there must me some wear and gradual decrease in pressure over time and the pump still seems to put out good volume but how low is too low?



I haven't run the fuel flow quantity test outlined in TSB 14-002-03, but from the amount of fuel the system put out when I purged the air from the injector pump schraeder valve during the 25 second lift pump cycle; I would suspect that the pump easily can put out 45 oz. of fuel in 26 seconds. The truck has about 22,800 miles on it. The truck is bone stock.



I am thinking about calling the dealer and telling them about the gradually worsening pressure and see if they will replace the lift pump under warranty. Evidently 5 psi seems to be the replacement criteria minimum pressure.



Any comments, suggestions, or ideas welcome.



By the way, this time I tried adding 18 oz. of clean diesel fuel to the filter housing bowl before I reinstalled the filter. When I threaded the lid down, the fuel just did come up to the lid threads but not run over. All I did after I torqued the lid to 25 ft. /lbs. was to purge about a half cup of fuel from the injector pump schraeder valve during a 25 second cycle until I heard the lift pump load down and loose a few rpm. She fired right up and did not miss a lick. Oo. Last time I followed the book instructions and spent about 2 hours purging air from the system after the injector pump ran dry and the engine died and would not restart. :-{} :{

 

[Chief USA]

Figured I would bump this back up to the top. Was hoping to get a few replies with some information and experiences.

 

[lcoblentz]

DC service techs will use the flow test outlined in the TSB, not pressure. If it produces the required flow, it is considered good.



I had a VP44 replaced under warranty, and the LP was determined to be good according to flow. I went to Cummins and purchased a new LP and installed it myself. Much better than killing another VP44.



Personally, I would go buy a LP, and change it out. Should be in the $150. 00 ballpark, give or take.

 

[Tcolesanti]

What lcoblentz said, I would change it regardless of what the dealer says. 6psi still is not bad but I would change it because in my experience it does not take long for the lift pump to die once it starts losing pressure.

 

[Chief USA]

Thanks, I called the dealer and have an appointment to bring it in to be checked and hopefully replaced this Friday.

 

[OTRPU]

I don't know what pressure is too low. Had a FP Guage installed on the lift pump today, I'm getting between 3 & 4psi at idle. Don't know for sure but think this is too low. Opinions?



Cheers,

OTRPU

 

[Johnny5]

At idle I would say that is too low. I usually drop 3-4 psi off the idle psi of 10-11, under throttle I can get 6-7 which scares me a bit but it has been this way since day one with the pressure guage on. If I had 3-4 at idle I would be checking in to it asap.



Altho I did have erractic prossure of 0-2 psi one time but that was when it was 15 below zero so I chalked it up to cold fuel but believe me I was watching it very carefully to get back up

 

[NevadaBackroader]

I just replaced my lift pump at 60K. It would drop to 5 psi at idle and go to zero at speed. It even pulled the 216 code, twice. After a day or two of this the pressure would return to 15/11. My first trip to the dealer resulted in an $80 charge to investigate. They ran a flow test on the lift pump. Since they didn't find anything failing under warranty, I got to pay the $80. They tried to get the code to trip again and couldn't.

Couple weeks later, it happened again. This time I went to Cummins and bought a new lift pump. Easy install and no problems so far.

Now here is the neat deal an old diesel mechanic told me about. When I changed the fuel filter, he had me button everthing up, start the truck and open the fuel filter drain valve with the engine idling. Be sure to have a big pan under the truck to catch the fuel. This purged the air and any water and, from the volume of fuel that shot out, I'd say it's a pretty good flow test. I did this again last night when I changed the lift pump. Both times the truck never missed a lick.

 

[Honker]

I just replaced my second lift pump today. I replaced the first one at about

35,000 miles. I was getting erractic pressure readings on original. When I replaced it the new one had readings of 12 lbs. at idle about 8lbs cruising at 2000 RPM and the lowest I could bring it down WOT was 6 lbs. I to started seeing gradual drop in pressure 8 lbs. idle cruising 2000 RPM 6lbs. and WOT as low as 2 lbs. I now have 72,000 miles and I just installed second pump today. Results 16 -17 lbs at idle, WOT lowest I got was 10 lbs. Did not get chance to go cruising yet. I can not believe difference in pressure readings in the two different pumps I installed, parts man said the only difference in the newer one I installed today is the plug in connection on the bottom of pump.