I had my center muffler removed to give my car a deeper sound, which it did! But now it seems I'm getting less gas mileage. I thought it was supposed to work the other way?!?!?!

 

What happens is you enjoy the sound so much you keep putting your foot down

 

OMG Phil!! Milage should be the last thing you should worry about. No one has ever asked me what my mileage is. Now on the other hand my commuter car is a 2012 Ford Focus that is running at 35.1 MPG.

 

Try "rebooting" your ECU, so the motor can "relearn". It is incredibly easy to do. Just remove the battery leads from the battery. Then connect the positive and negative leads together for five minutes - this will discharge some of the memory of the ECU; and it will relearn the motor next time you start the motor.
Rebooting should be done after every modification.

 

I'll give it a try!!
And I stopped driving my XF as much because she drinks like a ***** without a tab!! Lol.
And my XK 8 gets much better mileage!!!

 

Has it reduced the back pressure? If it has then it'll reduce the EGR and thus lower mpg.

 

"Has it reduced the back pressure? If it has then it'll reduce the EGR and thus lower mpg."

?

You have GOT to explain that to me.

 

"Seems" = you're not sure.

I'm betting that your mileage hasn't changed. The change in back pressure wouldn't be enough to change anything noticeably on these engines when the engine is being driven in the lower RPM part of the powerband as we do when we're driving normally in traffic, etc.

JMHO