Need some advice please! I have a 1999 2500 cummins with 87000 miles on it. Truck runs great until it hits 1/2 tank and then it just shuts down. I can put in a gallon of fuel and it fires right back up until it uses that gallon and shuts down again. I have replaced the sending unit which has the lp pump and verified that it is working. I have replaced the lift pump with a new carter even though old one seemed to have been working. I also replaced the relays even though old ones checked out to be good and while I was at it I replaced the overflow valve on the 44. It does seem to be a fuel delivery issue and as I say anything above 1/2 tank truck runs great. Any and all suggestions are appreciated! Thx.

 

Are you topping the tank off and then filling it again at 1/2 tank? You're putting half a tanks worth of fuel in when you fill it aren't you? The tank is normal shaped isn't it? Have you tried running it with the fuel cap loose? This will probably set an emissions code but it will make sure the suction isn't overpowering the fuel supply. I worked on a car years ago with a plugged tank vent. It sucked the tank is. When I opened the fuel cap, the tank popped back into shape. The guy was looking at major bucks but it was only the fuel cap needing replaced. I sold him a used one to make sure and saw the car for years afterward but never in my shop again.

 

thought of that but thought it was too easy. I will order a cap just to be sure, they are cheap enough. Its about the only thing i haven't replaced

 

Just leave it off and see what happens. Cheap and easy. If it works, great. If not, you're just out a little time.

 

Something else I just checked....should the LP pump that is part of the sending unit have power to it all the time when truck is on? I just checked and the 2 wires that go to the circuit board for the float and of course they have power with the key on but the wires going to the LP pump do not. Do these only have power if truck is running?

 

If it works the way I think it does, the lift pump will see power for about three seconds, then stop, until the PCM sees the engine turning. As long as the engine is running, the lift pump should be as well.

 

The lift pump mounted on the block below the fuel filter is okay, I need to know about the pump that is part of the sending unit. Just what is that for?

 

new info. Disregard my last post. just went through wiring diagram and I see that the pump that's in the tank is not functional in a diesel. Sorry, this is my first diesel so still learning.

 

I thought the pump in the tank WAS the lift pump? I take it that changed at some point??? Why would they put a pump in there, and not use it?