My 2001 has the wild "point me up-hill and I'll lose prime".I just replaced the tappet cover gasket,so I had all the feul lines off. This sounds crazy,but I think it is dumb luck it just started. The truck normally sets outside on level ground,lately it's been in a garage with the nose heading up. The truck has a edge box,4" pipe and a electric "helper" pump on the frame. It runs fine after it starts. 358,000 miles and the engine is pretty much original. I replaced the washers and rubber farrels on the fuel system. I've read 20+ times of this happening with no real answers. Help would be great. I will post with answers.

 

Going to guess this is a diesel? Should be a check valve somewhere in the fuel system. With the lift pump being moved out of the gas tank though, heaven only knows where it would/should be....