My friend Bob who just got the 06 HEMI XK a few weeks ago called me last night. A few days ago he swapped out the spark plugs with oem champions purchased from the dealer. He said that the plugs he pulled out were the same part number as the ones he put in and that they looked like they were original from the factory. His XK has 72,000 miles and the plugs that came out were shot with a gap of .060+. The new plugs were gapped according to the sticker under the hood and he said his Hemi runs so much stronger now but at the same time his MPG has dropped down significantly. The only change was the new plugs.

Now im not an expert on this but is it possible that the engine learned the gap of the old plugs and is now dumping more fuel to make up for the new plugs and better spark? Maybe the PCM just needs to relearn everything now with the new plugs.