I have an 07 Mustang GT. I got the car with 70k miles and have only driven 7k in the last year( about 77,500 now). I noticed that my exhaust was smelling really bad, like rotten eggs and sulfur. I thought that it was just because my car is cammed and it was just the way it smells. I also have the car tuned for 91 Octane and am running 91 from Sunoco. I fill the car up with fresh gas every week in the summer since I drive it more. Now I am thinking that the cats are starting to go bad. I put...

2007 4.6l Mustang - Cats may be going bad