Need Help, Fuel draining back

[JimT]

Which filter did you use?

I believe there are multiple (4) filters that will fit, but another forum member said that FS 19727 is the proper one for the ISX. It's 10 micron and I remember reading something from Cummins about using a 10 micron for the davco.

Personally I've had the exact same problem, last year. Had to keep adding fuel through the top cap to make sure it didn't suck air on a steep grade.

Another thing to check is the O-rings. Make sure the cover is on properly and that the o-ring on the top cap is sitting straight and not broken or missing.

I went so far as to replace the entire unit on my truck before I installed the FS19727 filter and didn't have any further issues.

There could be other issues too, such as a bad check valve in the unit, restrictions in the fuel lines from the tank, maybe one or more clogged tank vents, plastic davco cover warped and leaking air due to over torquing, could even be the lift pump. Although I'd start by checking the filter first. Seen a few other threads on here with the same issue recently (last few months)