hi, i'm new here and have read a lot of posts on this issue but none exactly like mine.
i have a 95 f-150 5.0 and last week my pump went on the front tank and myrear tank had a leak so i had never used it, but i knew the pump worked so i thought it would be easier and cheaper to change the rear tank.
well, once this was done i noticed that all my fuel in the rear was going to the front.
my front pump worked shortly but not for long and i had to go back to my rear tank which caused my front tank to overfill. can anyone help me with more specifics for my truck such as quick fixes or cheaper fixes or how to's? thank you

 

The front pump is bad as to why it is filling from the rear tank.

 

so if i were to replace the front pump it would solve this issue? i was thinking of just running off the rear tank if possible, and how/what would i need to do this.

 

You would need to block off (plug) both the supply and return lines at the front tank.
You can turn a bolts down to match the the fuel lines coming out of the front pump or you can cut both tubes off the front pump and close the ends by welding them shut.

 

thanks again for the quick response. this site has been really helpful.

 

I don't think the fuel pump in the other tank has anything to do with it. The electric fuel selector valve switches both the supply AND return lines between the two tanks. It sounds as though this valve has failed mid-position, such that it is allowing fuel from tank A to be returned into tank B.

These valves have a tiny electric motor in them, along with limit switches which turn off the motor when the shuttle spool reaches the end of travel.

I have seen these valves fail in such a way that the return path to either tank is blocked, and that can be a tricky one to diagnose.

 

There is not no such valve in a 1995 F-series truck with a 5.0 engine.
To be more direct there is no switching fuel valve on the trucks frame.

 

My bad, I should have googled before posting, I didn't realize that the newer trucks went away from the tank selector valve (my "new" truck is a 1990, old one is a 1979).

 

Your '90 doesn't have the valve either, that ended in 1989.

 

Yup, 92-96 only switch the power to the pumps, the check valve/shuttle valve is supposed to take care of the rest. You can buy the appropriately sized "fuel repair line" in the help section of the parts store, it'll already have the proper flare for the quick connect, cut it short and weld the end shut, plug it into the fuel line quick connect and that will do it.