ok, what fuel were running before you put 100 oct in the car and your cat is most definitley going out so if you get the sulphuric smell then your cat is melting or as you posted over heating to the point of melting...back to the pinging, if you are running anything under 92 oct then youll ping cause the motor is predetinating and if you run anything over the 92 youll be fine cause the cobras are setup to run only on high octane and nothing lower...so if you ran anything lower than 92 there is your problem. other than that, if it still pings then i cant tell you what the problem is. if you have any other questions just let me know.