Engine/Transmission (1998.5 - 2002) Lift Pump

[Midnite]

I was changing my fuel filter for the first time on my new (to me) 2000 truck, and instead of filling the filter cannister with fuel I decided to just bump the starter a couple of times and have the lift pump fill it.



Unfortunately, the lift pump is acting a little weird:



bump #1: lift pump puts out a good 15psi for the right amount of time.

bump #2: lift pump only puts out about 4 psi, but for the right amount of time.

bump #3: lift pump still only putting out 4 psi, but for about half as long as it should.



Then the lift pump just plain wouldn't come on at all. What's really strange is after letting the truck set for about an hour, I went back and it did the same thing. (1 good 15psi run, a wimpy 4 psi run, and a short 4psi run)



I'm guessing my lift pump is shot, but I'm just wondering if there could be some remote possibility that something else (preferably cheaper!) that might be causing this.



Thanks,

Mike

 

[cumminspwr01]

Once you have the engine running what is your pressure at? What is the pressure at WOT? Those are the numbers you should go by. My guess is your not giving it enough time between cycles. Try it once, let it sit for about five-ten minutes, try it again, let it sit five-ten minutes and do it again. I'll bet the pressures go up around fifteen each time you do it like that.

 

[Midnite]

Originally posted by cumminspwr01

Once you have the engine running what is your pressure at? What is the pressure at WOT? Those are the numbers you should go by. My guess is your not giving it enough time between cycles. Try it once, let it sit for about five-ten minutes, try it again, let it sit five-ten minutes and do it again. I'll bet the pressures go up around fifteen each time you do it like that.

Well, I can't even get the truck started now. Before I tried to change the filter, I had 12. 5 psi at idle, 5 psi at WOT, and around 10 psi at cruise.



Mike

 

[Turbo Tim 1]

You have air in the system, you either need to be quick or get someone to help you. Do a false start so the pump runs and crack the fitting going into the VP so that the system gets purged of air, tighten that fitting when solid fuel comes out and before the lift pump shuts off. Then try to start it, it may take a few cranks but should start. If it doesn't start you may need to crack a couple of injection lines.

 

[Midnite]

Cool--sounds like I need to do that.



Thanks!

Mike

 

[Ncostello]

In all seriousness... use extreme caution when cracking the high pressure injection lines. Hi Press diesel can kill you.



I'd say purge the air to the inlet of the VP44 however you want. Then instead of cracking the HP lines on the head... just floor it and crank till it fires. It might take 15-20 solid seconds of cranking but it will start. At least thats how mine does and I've had LOTS of air in the system before.



It will run rough for a second or two but just let it idle. It will come out of it.

 

[Midnite]

I'm not nearly fast enough to crack the banjo bolt going into the VP44 to bleed the air there, but flooring it while cranking worked great! So the truck is running, and the lift pump is still merely dying instead of dead.



Thanks very much!

Mike

 

[Ncostello]

You can loosen the banjo fitting a little and bump the starter. Then go as quickly as possible to witness fuel flow out the cracked fitting and tighten when fuel comes out. Makes a mess.



I took the Cummins pigtail adapter which is a plug harness to adapt the most recent lift pump to 98. 5-99 engine harnesses. I cut off the engine side plug so I had a lift pump male plug with the two wires. I soldered on long leads with alligator clips and I can clip it to the truck battery and plug the lift pump in to direct and constant 12V power. I let it run for around a minute solid then plug the truck harness back in. This normally gives the pump time to purge the air. ITs not hard to tell when the pump is pumping fuel versus air.



It will sometimes fire right off as if I had never touched the filter while other times it's the old "floor it and crank". You'll know which is which within 1 second. Depends on the attitude of the truck that day.