I have a 2004.5 5.9L. Suddenly the other day diesel started leaking as I was driving home. There were no apparent engine problems while driving (such as loss of power, smoke from the exhaust), just the diesel leaking from the engine. After looking under the hood it became obvious that the leak was coming from the fuel filter cap. There was not a visible crack in the cap, so we thought it might not be visible and only leak when tightened down. We replaced it with a brand new cap, and after 5 seconds of the engine running (turned over fine, again, no smoke), we heard a "pop" and the fuel filter cap began leaking. Thinking that we may have mis-threaded the new cap, we put it on again, checked the o-ring, etc... and it did the same thing again, and again. The truck has a fass hpfp 95 that has been operating fine for nearly two years. Everyone I have talked to has said that if it is a clogged return line causing the pressure increase that I would show excessive black smoke and would have trouble turning it over. I have yet to check the pressure on the pump itself, though the people at fass have a hard time believing that the pump could produce enough pressure to blow the fuel filter cap loose especially if the return line was not clogged. I am about to check the pressure at the pump and check to see if the return line is clogged but would like to have any advice possible to further diagnose this problem. Has anyone ever experienced a fuel filter cap leaking due to increased pressure?

 

plastic cap dont like much more than 15psi. they crack. need a aluminum one.

 

Tank vents are plugged.