I have a ford f150 92 I had to replace the value on the top of the tank last year on the front dual tank?

I have a ford f150 92 I had to replace the value on the top of the tank last year on the front dual tank because it was letting gas flow between the tanks and it worked fine but now the rear tank is pluming gas to the front tank so it will die if on on the rear tank but work on the front tank but you have to pump the gas to start it and it is a fuel-injected engine so I've asked many people about it and kept getting different answers can some one help me please!