I have a 2009 Jeep Commander Sport with the 3.7L V6.
This past Saturday as we were returning home, I noticed she was missing a little on hard acceleration. So, I made a mental note to remember to change the coils, plugs, and wires after the Christmas holiday. Little did I know that I did not have that much time, because by Saturday night the CEL had illuminated and I was getting P0303 and had a noticeably rough idle. I researched the code and found that it was misfires detected on cylinder #3.
Sunday, I decided to swap the coil with one that I had previously removed, because it was still working. She was okay for the day, but by that night I had an even rougher idle, and I was still getting the same code. I went back to my research and stumbled upon something called Carbon Tracking, which I had never heard of previously. Essentially, carbon buildup inside the ignition coil boot and down the spark plug will lead the spark to ground, causing the misfire. Upon checking my spark plug I could see there was a line of carbon going down the side of the plug and a line of carbon in the ignition coil boot.
So, I ordered new plugs, wires, and coils. In the meantime, I was able to clean off the carbon tracks and now have a much smoother running JC in the meantime, but I know it will not last.
There are a few explanations for carbon tracking:
1. Link #1 - Part 3 -Carbon Tracks are a Common Cause of Ignition Misfires
2. Link #2 - Carbon Tracking Causes Ignition Miss - TeacherTube
If you have any more information on carbon tracking, please post it here. I had a hard time finding any real information on it.