I have had my loudmouth on my 2002 SS for about a month now, and my mileage has dropped from about 22 mpg on my daily commute to 20 mpg. At first I thought it could just be a change in my driving habits, for example accelerating harder just to hear the exhaust, but I have made a point of easing around through the last few tanks. The car seems to be running normally. You would expect a free flowing cat back to either help or at least not hurt mileage. I was wondering if the loudmouth could have made the computer make the car run rich. I also thought the resonance/vibration could have caused some knock retard. Has anyone else experienced anything like this? Thanks for any help. PL

 

I had a guy on the other forum that suggested it could be because of winter. He said his mpg isn't as good during the colder months. This is my first winter with the car, and it didn't really get cold until about the same time I installed the loudmouth. Anyone else experienced reduce mileage during winter? Thanks, PL

 

I added my corsa just at the same time we had colder weather and I still picked up milage. About 1.5 to 2 mpg. I agree the colder weather makes milage worse so I was suprised mine was better. It has been consistant for three weeks.

I would think the LM would be as good.

 

You might reset your PCM. It has to relearn a/f ratio, spark curve, etc. That might help explain it. Maybe the car ran too rich and the PCM leaned it out too much, or maybe not enough. Reseting puts it back at default settings so it can then "readjust" it's self properly. I've haven't seen any mileage increase or decrease with mine except for the first tank, it seemed to go by fast, of course it could be caused by "trying out" the new exhaust.

 

At the time I put on the Loudmouth, I was driving 140 miles round trip to work. This was 99% higway driving. I got 25-26 mpg before and after with A4 and 2:73 gears. FWIW I still get about the same on the highway with the ST3500, but around town the mileage ain't so great.

 

Thanks for the suggestions. How do you reset the PCM, or where can I find the info on the web? Thanks, PL