About 2 months ago I replaced a set of NGK spark plugs with Champion platinum spark plugs and a several days later I started randomly receiving P300,1,2,3,4,5,6 DTCs and over the past several weeks the misfire codes have become progressively worse. I pulled the plugs and they appeared to be burning normal, but the problem persisted. Measured the CKPS ohms and reference voltage; they appeared normal according to Scanner Danner on YouTube.
So this morning I decided to go visit a friend that is a long time Jeep technician with more than 25 years of dealership experience. Spent the morning chasing down cylinder misfires....
He connected a factory diagnostic tool and read out the CPS while the engine was running; readings were very good.
Tested the cylinder misfires over a 200 second period with RPMs at 1800; way too many... so we retested again and they were really excessive.
Pulled the plugs and his response was "Why are there Champions installed" ? He promptly removed them and installed the factory recommended NGKs. Retested the cylinder misfires and now there were only a few. Next step was to spray Mopar Combustion Chamber Cleaner in the throttle body and then sprayed a lot down the TB throat and shut the engine off allowing the cleaner to dissolve the build up.
When the engine was restarted about 5 minutes later; there was a lot of smoke coming out which was all the build up from inside the combustion chamber.
Retested the cylinder misfires again and they were gone...
My friend said NEVER install those Champion platinum plugs again; they were the major cause of your misfires. He said that about 12 years ago Chrysler was having a lot of trouble with engines misfiring and the NGKs were the solution.