I have a 97' F-150 4.2, it's misfiring and has low fuel pressure, it starts rough in the morning but runs fine until it heats up or I shut it off then start it again then it misses horribly, if I keep driving it cuz I have to it progressively gets worse, the codes are #4 misfire/ lean, I've changed plugs/wires with motorcraft parts, bank 2 catalytic converter, fuel pump, fuel filter, fuel pressure regulator, MAF, it has no vacuum leaks that I can find, I've had motor smoked with no leaks, I've had coil tested and that's fine, plugs are dry when I shut it off, and there's no coolant leaks on motor, I've unplugged #4 injector with it running and plugged it back in and can hear the difference in the idle so that's working, I also took the valve cover off and checked the springs and after all that it's still the same so I'm stumped, any suggestions? It has 165k on it

 

Move the number 4 fuel injector and the spark plug to another cylinder to see if the miss moves. My guess is that you may have a stuck open or partially clogged fuel injector. If number 4 is still bad after moving the plug and injector a compression test is next.