I Have a '91 f-250 6cyl duel tank. my problem is after hesitating to start a few times, my truck finally would not start on the rear tank, but it would turn over consistanly. I found the fuel filter and check it. when i engaged the fuel pump there was a steady stream of fuel, upon switching to the front tank there was a jet stream to come out. After hooking the line back up, i tried to start the truck while on the front tank and immediatly it started and died. i tried to start it again, but it would just turn over. i tried again and had to unhook battery cable to stop it. when i turn the switch the pump sounds like it is engaging to long or not stopping at al. please give your imput and help me locate the fuel pump or pumps thanks

 

i believe fuel pumps for your truck are inside the gas tank. even if just one pump is bad, i think you need to replace these pumps in pairs. TSB's were issued for some ford truck fuel pumps, not sure if they apply to 1991. running out of fuel can ruin a pump as well. could be a relay or electrical switch problem. sorry couldnt be of more help.