I have a 1999 Navigator 4X4, 5.4L. It turns over but will not start. This happened a couple of times in the past few weeks but I finally got it started. Now it will not start at all. Finally got it started again by pushing the accelerator all the way to the floor. Turned the engine off. Starts right right up like nothing happened. Repeated this two more times. Started fine. Same thing happened a few weeks ago then the issue went away. First thought was a fuel pump but how likely is that the fuel pump can be intermittent? Tested to see if there was fuel at the fuel test port. Plenty there.
Today I used a fuel pressure gage. Got 32 psi running and 35 psi with just the key on (engine off). Was able to release the pressure and repeat test. Got the same answer every time. Pressure was steady in both tests.
Recently replaced the alternator. Alternator was faulty. This starting problem was there before the alternator issue and is still around.