I replaced my original lift pump at 50000 with a replacement 3990102 from cummins. It lasted 6000 miles and began surging. pressure went from 15 to 0 every 3 seconds. checked it with my own 15 psi gauge at the vp, ran a hose out and tied the gauge to the wiper and drove it. at any speed the gauge went from 15 to 0 every 3 seconds. took the pump out and bench tested with a 12 volt battery and ammeter. when I brought pressure to 15 psi the pump cut off and on . I tore the old pump apart and found 2 little thermal overloads in each leg. way in the bottom beneath the rotor. from what I could tell one of these was bad, now I am stuck for $185 as I carried the new pump for several months before install. I wonder how many other factory replacement pumps have these bad overloads? I have since went to a 4601hp on the frame with a big ole cat prefilter and screens out of the tank. works perfectly!!

 

That's some interesting info. Just so I've got it right, there's 2 overlaods on each leg...4 total?
If so do you think if you bypassed the bad one you could still use that pump as a back-up?
Do you have to do the Emission Test? We got it here in Nashville but it's not bad for a VP motor. I guess a turned up P motor would have to derate

 

I guess I worded it wrong, there is 1 overload per leg on the 3990102. I had to saw the integral retainer ring off the pump to get at the rotor and armature so pump is destroyed!!this is ok as the original pump was wore out, loose bearings and worn pump impeller. the thermal overloads are 2 little chrome objects in the bottom below the armature. when I tested the pump it pulled 2.5 amp and gained amps as I throttled it to 15 psi, then it started cutting out. Hope this helps, this lift pump problem is a factory defect and did not concern me too much till it hit me in the pockets. driftwood rattler 2001 clubcab 2500 shorty,gauges,fuel and boost, 6 speed,4wd, bone stock,so far