Pontiac Repair: 2001 GTP, resinator, resonator

Question
I have 2001 Pontiac GTP. I recently had the resonator replaced. I'm now only getting 10-12 MPG in the city, before I was getting 24-26. Would this have anything to do with the new resonator?

Answer
Hi Jason:

does the car seem to be running any different? is it lacking power? the only thing that it could be is if the resinator you had installed is causing the wrong amount of back pressure in the exhaust. if the part was aftermarket and not an origianl equipment part. Your milage is cut in half so I would have to say it's not running the same. Any service engine soon light on? if so that would be a place to start looking.. good luck :}