On a 2001 Mercury Sable fuel filter there are three lines... one going in from the gas tank and two going out to the fuel rail and/or injectors. What is this third line for and could it possibly be the reason I cannot get any gas to start the car? Electrical is good, fuel pressure is good @42, fuel regulator, relay & inertia switch are good. The fuel pump only came on once after 30 or more tries... the car started and then died again. Do you have any hints to this problem? Also, do you know the socket size needed to remove the fuel filter bracket? I have tried every size to know avail. I cannot remove the screw (maybe it is stripped, but I cannot see it, only feel it). Thank you in advance.

Isn't your fuel filter located just in front of the right rear wheel? If so, remove the "hair pin" clips, after depressurizing the fuel system, open up the aviation clamp holding the filter to the bracket, pry fuel lines from filter, and install new filter. Any screwdriver or 8 mm nut driver will open up the screw clamp.

If the fuel pump is still not starting every time, check the ignition switch for wear or pitting. Be sure to remove the negative battery cable first.