I just installed a magnaflow muffler(16 inch, round, stright thru stock piping) after i got back from Iraq becuase you know i wanted it to sound "cool". Been noticing my mileage change drastically is this normal?
I noticed similar conditions after I had a Flowmaster installed back in February. It was also really cold during that time too, so that could have been part of the problem. A few months later, I replaced one of the O2 sensors and my gas mileage started getting better.