('85 f250 6.9L) I have just replaced my fuel pump and return fuel lines because my truck was not running and had this same problem. The problem you ask? She pees while i drive (diesel drips at a concerning rate out the rear tank) and if i open the cap diesel rushes out.

Since it broke down last the fuel tank switch has not worked and is stuck on the front tank (which confuses me more to which why the rear tank is causing me problems)

Engine runs with no issue, except a random increase in throttle while accelerating (rarely).

I love you guys, please help she's my daily driver!!!

 

The switching valve on the frame is bad. That is one of their failure modes. It sucks the fuel out of one tank and returns it to the other.

I just got rid of my valve and hooked the front tank up all the time. I never really needed two tanks anyway, though it was nice on a long trip.

 

Thank you so much i'll replace it today!

 

It's not that easy you will find out. The valve that just goes right in from Ford is very expensive if you can find it. The valve at the local parts stores will work, but the hose fittings are different and the wiring is a little different. But it's much cheaper and easier to get. Both valves operate the same, it's just one was custom made to order for Ford while the other is a universal valve, both made by the same company, Pollack.