I have a 2002 F-150 Super Cab with a 4.2L V-6. It has 168K Miles and is very well maintained. Most mileage is over 55MPH Highway nothing over 75mph. The engine has a slight miss (almost a shudder) when slowly accelerating between 1400 and 1500 rpms. I changed the Coil Pack, EGR Valve, wires and plugs but the problem remains. I checked fuel pressure in the rail and it is steady as a rock @ 30psi. I get a OBDII code "0305" which is a miss on cylinder #5 but this code doesn't seem to coincide with the missing. I can clear the code, rev it a few times and go through the shudder and no code. Then as I am accelerating sometimes the code will set. I am really baffled as to what can cause a cylinder misfire code on only one cylinder only between 1400 and 1500 rpms. I cleaned the injector plug connections and it didn't help. I am almost tempted to just change the #5 injector thinking it could be an impedance breakdown at that certain frequency.
Any ideas? I checked all vacuum lines and connections for some vacuum leaks but again, nothing showed up.
The PCM has to see the misfire for a certain amount of time before throwing a code.
I would swap the two injectors as mentioned and see if the code follows the injector.
A compression test wouldn't hurt either. Hopefully, there isn't coolant seeping into the cylinder and fouling the plug.
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