2000 Ranger 4L misfiring
2000 Ranger, v6 4L 4WD
Started out running rough when cold for 30 seconds or so, then clearing out. After about a week of this it quit clearing out, meaning it would continue to run rough and the Check Engine light would come on. The code indicated #4 cylinder was misfiring.
Replacing the spark plug fixes it temporarily (I've done this 3X so far), then the cycle repeats after a couple days (misfire for 30 sec or so after cold start, later continuous misfires).
Replaced the fuel injector (twice, with new injector both times), flushed fuel rail. Didn't help at all.
Replaced cam position sensor, which had started squeaking in the middle of all this; didn't help misfire problem.
Replaced coil. Didn't help at all.
Plug wires were replaced at around 90K, currently at 111K.
Any ideas what to try next?