I have a 2000 3500 Dually with a Cummins in it. It has a FP100 Airdog lift pump on it and no other mods. About 3 tank of fuel ago it started pushing fuel out at the sending unit and now pressurizing it enough that it is coming out of the filler on a full tank. The 3/8 vent on the sending unit was capped from the factory and there is a 1/4 inch vent that is open. It also about the same time started not holding a prime if left set for more than an hour or so. The prime thing might be the pump according to the guys at Airdog, but the pushing out the fuel has us all baffled.... Any thoughts or help would be greatly appreciated.


CP

 

Sounds like your vent is clogged somewhere else along the line. Think I would start with checking that entire system.

 

Well, I had already been thru all of the vents, and all of the fuel system from the filler hose clear to the injector pump. What we found was the injectors were bad and the front three hold-downs were only finger tight. This was allowing compression the get back thru the return line and in-turn was pressurizing the fuel system. Also after testing all of the injectors, After 268,000 miles, they were anywhere from 900 to 1000 lbs below minimum pop. Hope this helps someone else in the future.


Corey