alrighty i have a 90 f150 with the 4.9 I6 and a 5spd... new trans/clutch/alternator and pump... so when i bought it, i knew that only the rear tank works... which is fine for what its going to be used for, its not my daily driver, its not even titled in my name yet, just wanna work out some of its problems... fuel being the biggest one... so when its running for about 10-15 minutes, it will completely drain the tank of gas, and magically it will all go to the front, there is a recall about this, but i guess it isnt under warranty after 12 years... also the guy i bought it from bypassed the fuel pump relay, which is kinda ghetto, but ill post up some pictures later today about that... is it possible for me to fix the check valve in the fuel pump/sening unit... and how is that done?

*EDIT*
also would it most likely be the valve in the front or rear pump thats bad, seeing how the rear pump is the one im using?

 

alrighty, i got the fuel pump relay put back in correctly. so it doesnt run when the engine isnt running... i still am dumping fuel into the front tank, from the rear... and my front right brake line is leaking... any input?

 

Sounds like the fuel tank switcher is messed up. Maybe an o-ring or valve has given out. Just replace the whole unit.

 

The problem is with the return valve in the tank which is getting the fuel transfer, in your case the front.

 

where exactly is the fuel "switcher" located... sorry im kinda a newb to the f150 scene, its kinda my daily while my 240sx gets turbo'd (obviously not my daily yet)

 

Its on the driver side on the frame rail about midway.