I have a 1998 F-150 4.6 191000 miles ,I have replaced coil packs,wires, injectors, throttle body,mass air flow,plugs still missing out on idle and under load but you can hold throttle at 1500 rpm you can hear miss and feel it,it will try to smooth out then goes back to missing and fuel pressure 30 to 40 psi any help would be appreciated!
@Mamba2485 Recommended fuel pressure is 55-85lbs When was the last time you changed the fuel filter ? Could be the fuel pump driver module or the fuel pump it self. That is an expensive pump module. Since you have fuel pressure I wouldn't think it's the module. The fuel pump could be getting weak if the filter has been changed very recently.
If you go through everything fuel wise, ie filter change first. Check the tank expansion vent line. Mud daubers, and dirt bees can plug this line causing the fuel tank to not vent and draw suction on it making the fuel pump work harder over time. Usually the symptoms are if this is the cause, runs great for a while, then gets worse and worse.
