1989 Ford F-150 100,000 V6

Back in your trucks day they had a TSB (tech service bulletin) about that, they installed check valves on top of the tank on the pressure lines (big ones). Problem is that I havent been able to find them anymore, which means you will have to install a new fuel pump in the front tank. If your truck has a metal cylinder between the fuel line and tank unit, remove it and check the inside for debris, I have cleaned them out before and had them work again, but that is only if you have it in the first place. Updated pumps have a check valve to keep this from happening