No 3 cylinder misfire

[Tryfan]

2001 XJ, AW4, I6, AC

I seem to be having a classic hot soak problem (rough running after re-starting the Jeep after a short stop at a store etc) although it's not been that hot out except for one or two days and now have a CEL P0303 no 3 cylinder misfire. I have had hot soak issues occasionally before but recently this has become very persistent and now I am throwing the P0303 code frequently. I have to sit with the hood up now for about 10 minutes before I can get her running. Once the jeep starts it drives fine but the idle is slightly erratic.

I was thinking of replacing the no 3 injector probably original 150000 miles but for now until I am sure this is the cause I only wanted to replace the no 3 injector rather than all 6. Do you think this would cause any further issues just replacing no 3 will it put the other 5 injectors out of balance?

I have NGKs spark plugs with about 16,000 miles on them and I would think they should be ok at that mileage but I haven't pulled no 3 yet. I wouldn't have thought the coil pack would be a problem because I would expect a misfire on one of the other cylinders (3 coil packs, 6 cylinders). Any advice you could give would be greatly appreciated as this is driving me nuts, I also have to drive about 800 miles next week and would like to resolve this before that trip. Thanks.

 

[md21722]

You really need to diagnose the issue. The last years of Jeeps had problems with valves not turning and cartooning up causing low compression & misfiring. There is a TSB on it. It could be an injector, plug, or coil as well. I would pull the plugs, inspect, and do a compression check first. I would not rush out and buy parts, though you may want to swap injectors between cylinders to see if the problem moves.

 

[Ecomike]

I would swap the @ and #3 spark plugs and inspect them to see if #3 is running lean or rich using the visual spark plug photo inspection guides.

Then swap injectors #3 and #4. Then see if the problem moves to #2 or #4 cylinders. If it stays at #3, you have eliminated the injector and plug.

You also need to run a fuel pressure test right away. The fuel pump FPR in the tank or outlet hose may be leaking/failing and the pressure may not be high enough.

Check the coolant and oil as that year head is know for factory defect cracks forming around 100,000 miles.