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 for 3 weeks straight. I use to get 400 miles with 13 gallons now only 200 miles.

 

Could it be because my car lost a little low end torque

 

was the driving habit you tried out for 3 week "pedal to the metal"? your engine may be using a little bit more fuel than before. why i dont know just cuz i guess

 

The driving habit was mostly keeping the rpm under 3.

 

No, the cat-back should have nothing to do with fuel mileage UNLESS the better sound makes you keep the revs up. Double-check your actual mileage and if you are really getting an average of 14 MPG, take it to the dealership - something is wrong and it's NOT the cat-back!

 

first thing i want to know: how are you guaging your MPG?

 

Before having the catback,I filled my tank to near full at least 10 times after the breakin period (7000 mi). I remembergetting over 400 miles after every fillup. Since after the catback installation, I noticed as I was driving home my car was eating up alot of gas and since then after every fillup my car at the most gets 220 miles on almost a full tank.

 

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I decided on this weekend I'm getting a performance diagnostic test because I might possibly have bad or faulty O2 sensors.

 

I still say go to the dealer they might diagnostic for free since it's still under warranty