Persistent P0303 code

[Kruzn]

Our '06 Renegade is running well except for a persistent P0303 (cyl #3 misfire) code. I replaced all six plugs and the coil on #3.

It will run just fine for a week or two, then will intermittently start to miss slightly which is really only noticeable at idle. It "seems like" it happens more often when it is damp out or raining, but can't say for sure. After it misses for awhile, it trips the check engine light.

The miss will go away on it's own for a while. I clear the code and all is well until it does it again.

I've also tried running some fuel injector cleaner through it. I'm on second tank of fuel with cleaner added.

Any ideas?

 

[HoosierJeeper]

http://www.jeepkj.com/forum/f196/random-misfire-conundrum-61220/

Check this thread out- it was similar to your issue. Welcome to the forum.

 

[Kruzn]

http://www.jeepkj.com/forum/f196/random-misfire-conundrum-61220/

Check this thread out- it was similar to your issue. Welcome to the forum.

Thanks! Somehow I missed that thread. Very helpful info. I'll proceed with checking crank sensor first.

Appreciate the help!

 

[yippee]

I had the same problem, went through the same steps (plugs and coils) and was still having issues. I guess it's worth asking, what spark plugs and coil did you put in the Jeep? From my understanding these Jeeps don't take well to anything other than the NGK copper spark plugs and the Mopar coils. I wasn't one to argue with what works, so that's what I put in the Jeep.

I ended up replacing the Camshaft Sensor and the Crankshaft Sensor at the same time, since neither one cost a whole lot and they were both potential suspects. Again, I went with Mopar on both items. I changed the Cam Sensor first and didn't notice much improvement. Later I changed out the Crank Sensor and so far, no more issues (knock on wood). It seemed to idle smoother after that, and so far no more CEL.

If you're experience is anything like mine, I would say the crank sensor is your culprit, and once you fix that you should be good to go.

 

[Kruzn]

I had the same problem, went through the same steps (plugs and coils) and was still having issues. I guess it's worth asking, what spark plugs and coil did you put in the Jeep? From my understanding these Jeeps don't take well to anything other than the NGK copper spark plugs and the Mopar coils. I wasn't one to argue with what works, so that's what I put in the Jeep.

I ended up replacing the Camshaft Sensor and the Crankshaft Sensor at the same time, since neither one cost a whole lot and they were both potential suspects. Again, I went with Mopar on both items. I changed the Cam Sensor first and didn't notice much improvement. Later I changed out the Crank Sensor and so far, no more issues (knock on wood). It seemed to idle smoother after that, and so far no more CEL.

If you're experience is anything like mine, I would say the crank sensor is your culprit, and once you fix that you should be good to go.

Thanks for sharing your experience. I haven't messed with it any more yet. I did use the NGK copper plugs, but I got the coil from Napa. Probably should try the crank sensor next.

Appreciate the help!

 

[yellocoyote]

Happened one with the crank sensor on my old KJ as well - same symptoms, easy fix. Hope it's also a simple fix for you.

 

[Kruzn]

Fixed

It was the crank sensor. Idles nice and smooth now with no check engine light and/or codes.

Thanks for all the suggestions! :icon_biggrin:

 

[Kruzn]

Spoke too soon...

I guess I spoke too soon! :icon_mad: Crank sensor did not fix it afterall.

Started missing at idle again today. Check engine light came on. P0303 code again.

Before replacing cam sensor, I think I'll try swapping the Napa coil on #3 with one of the other cylinders and see if the code changes.

 

[HoosierJeeper]

That's what I would do.