2014 with Roush 590 package. Developed some misfire at 35,000 miles and took to Ford dealer that handles Roush, but they were no help. Decided to change spark plugs and found the center electrode on lower plug on cylinder number 7 burnt up pretty good. Remaining 15 plugs looked good and gapped correctly. Replaced all plugs and no more problem. Any one have this happen or an idea why the one plug was burnt up? Bad plug? Bad coil?, Injector? Maybe just a bit of bad gas? Thanks for any ideas - trying to prevent from happening again. I am told the Roush tune runs it rich, so maybe even this could be part of it. ???