When I switch to the rear tank on my '89 ford f250 it pumps all the gas to the front tank that is all ready full. Why is it doing this?
This has started after we put new fuel pumps in both tanks.
You will have to change both fuel pumps and filter and ford makes a check valve that goes on both fuel pumps that will need to be installed. This is as per ford tsb's.
Were the fuel pumps motorcaft/ford?
It's not the fuel pump that's the problem. It is the metal lines the fuel pumps attach to. They have a built in check valve and they are blown out letting the pump push fuel into the other tank. That is why it has to be ford complete unit fuel pumps.