Installed greddy supercharger a couple months back. Now rear bumper is turning black from exhaust. A/F seems right @ 12.75. I performed compression test and cylinder leak down test. All check out ok.
Your car is a rich pig. Nothing you can really do about it except lean out your a/f ratio or clean it off with a rag every once in awhile. Don't get a ghey CF cover thing for your bumper exhaust outlet whatever you do though.