Check Engine Light, Code:P0304 Cylinder 4 Misfire

Vehicle Specs: 1998 XJ 4.0L
Just last night my check engine light came on. I went to Autozone this morning and had the code checked. It was pulling a P0304 - Misfire occuring in Cylinder 4.

I pulled the plug and wire in #4. The plug is gapped at .035 which is to the spec in the FSM and the wire is pulling 10K ohms, which is within spec as well.

I have read posts suggesting the coil and low fuel pressure, but I would think that I would be having more issue than just CYL4 if it was either of those.

Any suggestions would be appreciated.

Thanks,

It very well could be your injector.

Is there a way to test to see if the injector is bad?

I checked the resistance on the injector and it was 13.4 ohms. Which is within the specs. Are there any other tests to see if the unit is bad?

Try swapping it with another cylinder and see if the misfire follows it. You could do the same with the spark plug and the wire.

a coil wont make it misfire on only one cylinder. i would move the plug to #3 first and see if it follows, then the wire. also check for a cracked dist cap.

Process of elimination for a single cylinder miss. I rely heavily on the "swap and follow" strategy whenever possible.

1. Replace distributor cap and rotor; inspection sometimes not conclusive
2. Swap plug
3. Swap plug wire
4. Swap injector

I think I am going to do a complete Tune-up. It has been approx 10,000 miles since I bought the Jeep and it is just hitting 100K. Wires, Plugs, Cap, Rotor, Oil Change etc. Then the injector if necessary.
I will update once this is complete. Most likely this weekend. Thanks for the assistance so far.

Well, I just got done with my trip to Autozone. I purchased plugs, wires, rotor, cap and one (1) injector. Total $153. After replacing all but the injector she was purring like a kitten. The Cap and Rotor must have been OEM because the rotor was all corroded an the inside terminals on the cap were covered in black debris. Tomorrow I will take back the $70 injector and re-coop some of my cash.

Next on the list is repairing my rear hatch that opens 1 out of 10 times, replace the struts on the rear hatch and use the old ones to hole up the hood, replace my headlights (both are cracked from rocks and one has a hole in it), fix front passenger auto door lock. I think that is about it.
See ya all next time, and Thanks again.