YJ misfiring.

It has been 13 months since the Jeeps last tune up.  The odometer does not work but I estimate around 3000 kilometers max.  My Speedo is actually in Kph, annoying but it is  going to be replaced soon.  The four plugs below are the ones that came with the Jeep when I bought it.  They were not too terrible.  The brand was Champion.  Once I seen that they had to come out.  My luck with Champion plugs is terrible.  These were removed November 2014 along with the cap, rotor and plug wires.

 So these were removed in January 2016.   They are Autolite as was recommended on Jeep Forum.

 

All the plugs had worn away electrodes.  They looked like crap.  But I found the problem when the number 4 cylinder pug was pulled.  The ceramic insulator was cracked badly.  I believe this to be the cause of the misfiring.

The plugs, wires, cap and rotor were all replaced at the same time.  It runs like a top now.  I am curious as to what was the reason for this plug failing as it does.  The Jeep does not get abused.  I did run it at 70 mph on a 3.5 hour trip to Orlando and back.  But it worked fine on that trip and after that.  The only fuel additive I use is Seafoam once in a while.  That mostly dries out the gas.  Around here it is common to install a water separator in the fuel line, same one used on a boat.  Perhaps that will come next for my Jeep.