I recently bought a 95 cummins. The first start every day it would run really rough,puff white smoke,and sometimes die when put in gear. Once it warmed up it was fine. I realized it was only idleing at 400rpm so i took it up to 800 and it ran perfect for 2 weeks. Now its back to the same thing even idleing at 800. I drained the water seperator and its still progressively getting worse. Could the lift pump slowly be going bad? Any ideas? thank you

 

yes the lift pump could be bad, start with a fuel pressure test then i would also do a compression test.

 

Ok so i changed out the lift pump and took out the fuel heater. Neither were the problem. Can someone walk me through how you test for leaks by pressurizing the tank. Thanks