2002 Jeep Grand Cherokee- 4.7L V8-I am getting intermittantly a Cylinder 3 misfire code on the OBD II. Codes 353 300 303 though occasionally a 304 (cylinder 4 misfire.) I have moved the coil, fuel injector, and spark plugs to other cylinders, ohmed out the control circuit for both the coil and injector which show continuity to the PCM, cleaned the connectors on the PCM and common 12V side of the harness yet still get the error- plus a rough engine running which clearly sounds and feels like the cylinder is missing. The problem was coming and going- but now is more permanent it seems- any suggestions?

Regards

Perhaps you could buy new spark plugs for #3 ,an even #4 if you feel so inclined. Bosche Platnum, Platnum 2, and Platnum 4 are all winners. Are the #3 and #4 plugs different at all to the others? Then there is your answer. If not, then the firing timing is off and then would require replacement for peak perfromance. Or you could replace all 8 of them and have no problems for a long time.

This is my 200th post, I thought I should just throw that in there.

Thanks- Actually I just bought 8 new Bosch plugs and will install them today- thanks for the advice- I'll be back if this doesn't work for any other suggestions that you may have.

Code 353 is a coil fault code. Make sure there is no arcing check at night with a spray bottle of water. Also check the plug wires at cylinder #3 & #4. Since you have moved the injectors and there is still a miss try to isolate #3 cylinder. You might try a compression check on #3 and compare with the other cylinders. Take the valve cover off and see if the valves are working properly on #3. Check the coil, plug and wires first.

Thanks- I replaced the plugs and am now just receiving faults for Cyl.3 303 and 353- Misfire and Coil. I had moved the coil previously so I do not think that that is it. I was able to identify the wiring from the PCU for the coil and injector- ohmed it for contiuity but where is the common tie point for the ASD relay which supplies the 12V source voltage for both the Coil and the Injector? I am suspecting that if it is not the valves- which I have not checked, then maybe it is at the common tie point for that part of the circuit.

Found the problem- the pin for the control side of #3 coil was expanded out towards it rear so that while looking into the connector- it looked good, it wasn't actually making contact with the coil- removing the pin from the connector and reshaping it fixed the problem!