Rep Power: 0

I still can't figure out why my honda civic 07 automatic waste twice more gas after I installed a catback exhaust. I've had the exhaust for 4 months and I even tried the same driving habit "keeping the rpm under 3" for 3 weeks straight. I use to get 400 miles with 13 gallons now only 200 miles. Could it be because more car lost a little low end torque?

 
Rep Power: 388

Do you have all the sensors in, or did you have to loose one? If so, the ecu isnt getting the signal back that its adding enough fuel, so it adds more... resulting in less miles per gallon. Check your sensors.

 
Rep Power: 0

I had it professionally installed, how could I lose a sensor in the first place?
I'm still willing to get it rechecked.

 
Rep Power: 352

^he said a LOOSE sensor....not lose a senor...

a loose sensor makes a big difference.

 
Rep Power: 250

yep, they prolly just put a eliminator on the loose sensor so you wont get those CEL. just open your hood and check it around your header to exhaust part.

 
Rep Power: 0

What does it look like?

 
Rep Power: 388

I ment did you loose a sensor... if one is loose it will also make a difference. A simulator or emulator or whatever u wanna call it- its basicaly just a spacer between the sensor and the bung to move it out a little bit, usually on the 2nd O2 exhaust sensor. You have an 8th gen right... If you can, please take a picture of your header and anything going on with the pipes after it. I'm pretty sure your missing a sensor in one of them (looks like a spark plug with a wire attached to it that screws into the pipe), or some other issue with the sensor.

 
Rep Power: 225

this may sound stupid but shouldnt you be consulting with the people who "professionally" installed your exhaust system? after paying them to install it they should be glad to help you with your problem! after all they did do whatever is causing your mileage to suck.