Champion Spark Plugs
I looked up the required spark plug on the Champion Spark Plug website and got a number of RN11YC4 (322). Then checked the owner's manual and the shop manual and got a number of RN9YC (415). The plugs in my '94 D90 with stock 3.9 look to be original (70,000 miles) and they are RN11YCC. I'm all checked out on what the numbers and letters stand for so I know that the 11's are two heat ranges higher (hotter) then the 9's, otherwise, the plugs are identical. I pulled out four of the plugs and they show no signs of running hot. So what gives, what am I missing and which Champion should I be using, or am I obsessing over nothing (yeah, like that's never happened before).