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2001 ford ranger engine mis fire

engine misfire #4 cylinder,code p304. Truck has 34000 miles. Replaced spark plugs and wires.No improvement.Mis is not always present.This is a 4 cyl. eng.

Does it run rough and misfire when cold, but runs better when warm? If so, I’d be looking for a head gasket leaking. Otherwise, cracked dist. cap? Bad rotor (if it is not DIS), lost bad crank sensor, ???

It’s not the crank sensor. If it were, the engine wouldn’t run.

The next two things to check are the coil pack and the fuel injector for cylinder #4. Check the resistance of the coil pack to see if tower #4 measures different than the other three towers. If it does, that’s probably what’s causing the misfire. If the coil pack checks out fine, then try swapping the fuel injector for cylinder #4 with another cylinder. If the miss moves with the fuel injector you know it’s a fuel injector problem.


You are right on the money. I’ve swapped the injector with a different cylinder and am waiting to see what happens.Will you explain how to measure the coil resistance. Thanks, I appreciate your help. Bob