Well if I ever really get on it there is this really fuggly smell of like rotten egg or something unpleasant. Anyone every experience this? Exhaust system was just recently replaced. Could it be a coating continuing to burn off or something in the cat?

 

Yep, all new cats smell like this when you first put them on. Nothing to worry about.

 

sweet

 

Normally you wont smell that even when new, but under WOT with extra fuel present, the cat can heat up and make that smell. IIRC, its the small ammount of sulfer present in gas being converted over to sulfer dioxide by the high temps/catalyst in the cat. That smell is the equivelent of the canary dying in the mine. Its a sign that the cat is excessivly hot. From what Ive seen, GM tends to lean out the AFRs a tad on the low and high ends of the rpm band to help minimize power loss, so that may explain it. If your loosing fuel pressure under load or the engine is going leaner then whats needed to shut down the cat, then youd also smell that. This condition will also melt the cat if it goes on for long enough.