Jeep Cherokee Spark Plugs


Many people ask about what spark plugs I recommend in the Jeep 4.0 engine. I prefer the Champion RC9YC. Many people cross this to the Autolite 3923 which I have also used successfully. However Lee of Hesco has this recommendation:

The plug for the 4.2L head that works is the RC12YC @ .037 gap, if you get ping try RC9YC @ .045 gap. The 4.0L head likes the RC9YC @ .040 GAP.

In my daily driver I am currently running the Champion RC9YC with a .045 gap.

I have experimented with things like the Bosh platinum and other expensive plugs. However the standard Champion plugs seems to work the best. The Autolites work almost as well and will do when I can’t get the Champions. Lee says that the Autolite is a hotter plug and can cause pinging.