fuel tank selector valve

[tippiestminotaur]

I have a 1990 f 250 with a inline 6 efi, dual tanks.the truck will run on back tank but pumps overflow into the front tank .the front tank allows idling but no acceleration as if it was getting no fuel.This only happens under load . I am assuming that the fuel tank selector valve is not functioning correctly.My problem is I cant locate where the fuel tank selector valve is located as autozone shows 2 different types a 3 port and a 6 port. i want to make sure i get the right one b4 i tear it apart

 

[dustybumpers]

There is no fuel selector valve on a 90. that stopped in 89.
Your truck has a fuel delivery modual in each tank.

The FDM in the front tank has 2 problems

1. it is failing to keep pressure
2. the check valve on the return line has failed, allowing gas to be pumped into that tank when it is not running

Your repair will be to drop the tank and replace the FDM.