The fuel line exiting from the top of the tank is part of the evaporative emissions systems and terminates at the blue painted (charcol filled) canister located in the right rear portion of the engine compartment (ahead of the heater core). The fuel pump return line DOES NOT connect with this line.
The mystery second fuel pump line everybody is discussing here is a return line from the fuel pump back to the tank, entering through the sending unit assy. On cars with this feature, the sending unit will have TWO line fittings, one 3/8" (like all hi-po cars), and the second one much smaller (5/32"??). The fuel pump then has three fittings: 1) The 3/8" input from the tank/ 2) the steel line to the carb./ 3) The 5/32" return to the tank.
Which cars had this feature? Beats me! I have heard it was all a/c cars or all Q-Jet (CJ) cars, or all CALIF. smog cars, but have never been able to confirm which is true. I do know my a/c, CJ, CALIF. car has this set up.
I have heard the reason for it was high underhood temps would cause fuel boiling and related flooding problems. The fuel pump return line outlet port has a reed valve which opens under these conditions and allows pressurized fuel to bleed off back to the tank.
I do know that as these pumps age, the return line reed valve can weaken and, under certain conditions, pump most of the fuel back to the tank instead of the carb. When this happens, the engine will quit when any power demand is put on it. It will feel just like a bad fuel pump (which it is), but the pump will check out OK when you perform the on-engine test shown in Ford's shop manual. Very frustrating to trouble shoot (guess how I know!). A quick fix is to plug the return line.
If you obtain a new Ford fuel pump from a dealer, it will only have the inlet and outlet fittings, and you must plug the return line fitting at the sending unit.
Posted on Sep 15, 1999, 10:14 PM from IP address 152.163.201.63