If you have an empty catalytic converter, the car will backfire when you let off of the gas. With an empty cat the exhaust gas will bottle neck inside and pop or backfire. There are ways to prevent the backfiring while keeping the empty cat, but will render the exhaust system illegal. What kind of exhaust are you using? -----Dani B. #5003 To address comments privately to the moderating team, please address: moderators@xxxxxxxxxxx For more info on the list, tech articles, cars for sale see www.dmcnews.com To search the archives or view files, log in at http://groups.yahoo.com/group/dmcnews Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/dmcnews/ <*> To unsubscribe from this group, send an email to: dmcnews-unsubscribe@xxxxxxxxxxxxxxx <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/