[jfw432]

I originally bought the K&N cone filter for my Jeep and that gave me 1-2 extra mpg. I then bought a high flow catalytic converter and a free flow muffler and that dropped my gas mileage 3-4 mpg. Everything I've ever read says a less restrictive exhaust gets you better gas mileage. I noticed performance gains with the K&N filter but nothing or little change with the new exhaust.

I checked the ECU and got no code readouts so I assume that all of the sensors are good. I've had the exhaust for 3-4 months at least and reset the computer when I did get it.

The sound of the exhaust is really loud at 1500 rpms and when I'm hard on the throttle. Hard on the throttle I consider normal but the low rpms noise gets me and I don't understand it. Could there be a leak somewhere that is causing a problem? Would a small leak cause the huge decrease in gas mileage as well?

Any help or recommendations are appreciated because I'm stumped and the low gas mileage is killing me.