2006 Chevy Impala SS

over the past 2 years, I’ve had to replace the #7 spark plug 4 times. the porcelain on the bottom of the plug is completely gone (turns to white powder) and also turns black where the threads are. using AC Delco plugs.

Also, after coasting for a bit, large cloud of smoke comes out of the rear.

This is probably worth a look at TSB’s. I would think you would find something about the sparkplug.Anything ever go wrong with the wire? tried a different kind of plug?

Anymore details on the smoke (color),are you up on service? what type PCV does your car have?