I was chasing a misfire and didn't think to check the plugs. They were replaced about 3 years ago and have less than 20K on them. I pulled the plug on the missing cylinder and it was all black and a huge ring of carbon I guess on it. I replaced it and plan on replacing the rest here soon but was wondering what would cause it to foul so badly?

I hardly ever drive the Maxima. I just recently replaced the fuel filter in it.

 

well possibly just a bad plug, also check the wires too.