1992 Mercury Marquis car not starting

i have a 92 mercury grand marquis 4.6l v8, my car will not start, it tries to at times but the engine wont fully turn over. my engine is not seized I have cranked it over manually, I have replaced the starter, starter solenoid, battery, spark plugs and wires, oil, oil filter, and fuel filter. with no success, i have also tested the coils, edis ignition module, battery cables, negative cables, ground cables, they all read fine. I have no idea what to try next to see if I can get my car running, please help!