Re: 1994 F-150 Fuel system problem
Well, my first thought is that the fuel pump on the front tank is failing. While fuel pumps usually quit all at once they do actually wear, becoming less efficient with time. Another thought is that there is crud in the one tank that is plugging your fuel inlet on the pump.
Now, correct me if I am mistaken, but I think the two tanks share a common fuel filter on the frame rail. This would suggest that at that point your system is good.
It wouldn't hurt to change that filter anyway, but it sounds like you are going to have to drop the front fuel tank to solve this problem. Either to clean the tank out and/or to replace the fuel pump.