Well for those that didn't know, my exhaust setup is completed (Comptech header/Car-sound cat/Comptech catback). I thought I'd make a post about it because I noticed something out of the ordinary. It was expected that the ECU might run in closed loop at partial throttle.

I was also expecting that the car might run rich and a decrease in gas mileage would follow. I've read numerous threads online about cars running rich with a full aftermarket exhaust setup. After resetting the ECU and taking a trip to the gas station, I've noticed the opposite.


With the stock setup I couldn't even get close to 150 miles to a half a tank. Now with the Comptech setup I hit 160 on a half a tank. Keep in mind that I continuously go to the same gas station and use the same 87 octane (no tune-up was performed on the car). It could be just a freak coincidence or do some people actually notice an increase in mpg with an aftermarket exhaust system. Maybe the OBDII gremlins are just being nice this time around.