n/a_threat

what is the difference, when would you use either one?

mself52

k from what i understand....
99+ mustangs have returnless fuel system meaning the fuel pumps are only sending fuel when the computer tells it too...and fuel cannot return to the gas tank

and pre99 they had fuel pump that was always on so fuel pump was continuesly pumping fuel to the motor if the fuel wasnt needed it went back to the gas tank....