I helped my friend install a new cat back 2 days ago. He just called me to tell me that his gas millage is HORRIBLE. I was thinking it was cause he got on the gas more, but he says he hasnt. Is this common, should we try to disconnect the battery over night or something? Any help is great.

 

check for exhaust leaks. taht can cause a rapid decrease in MPG.

 

im not really sure about this... but i think that because more air is coming out from the exhaust and its burn more gas... just like after i install my inake it eats up more gas... so i think thats should be common

 

intake = > mileage (if you are driving the same)
you probably notice lower gas mileage cause your foot started getting heavy

 

Let me educate you.

Acura is picky about their emissions. The modern emission systems have a million sensors designed to REDUCE emissions. These sensors were very very tuned for a stock car. I have seen people with open exhaust systems loose horsepower. The motor has to be tuned. The ECU is going to see a change because of an altered exhaust flow (YES, I'm not kidding, the K-series are really this picky.) For some cheap power, add an intake and reset the ECU. By ******* with the exhaust, the bad MPG is probably from the sensors reading something that they didn't like and overcompensating or doing something wierd. I don't have any specifics, please check google and honda-tech for more information, but I'm not kidding when I say you can put the B and D series type bolt ons to a K-series and possibly loose MPG and HP. First thing, reset the ECU and start up the car. Then, check for exhaust leaks. Then check any electrical connection problems. If its still ****, get on the internet and see what could have caused it man. This is all I can tell you.