About a week ago the cat'verter, the 1 under the front seat area, fell off due to rust. I put a pipe in it's place til I can afford another 1.
I noticed a BIG drop in gas milage!!
Other than emissions, what does it do???
Is it a contributor to gas milage???

Half a tank in 3 days used ( about 90 miles ) compared to almost twice that!!??!!

Thanks for ANY & ALL tips, advice, & education!!!

The catalytic converter should not be affecting your gas mileage -- a unplugged cat (and it requires serious engine problems to plug up the cat) flows nearly as well as an open pipe. I'd be more inclined to blame problems in your exhaust system from the temporary fix.

its more then likely the O2 sensor that is reading things wrong.

The catalytic converter is essential to sound reduction, emissions and helps maintain your engine's correct back pressure. Other than that your car should run just fine, but I would suggest replacing it when you can afford to. Don't wanna be the guy running around with the exhaust system cut at the headers lol. Hope we helped!

i have headers and full 2.5" piping no cat, its not really loud, resonator and muffler play a big role but your question is, when you have an exhaust leak you also tend to stomp the gas more to get power, on top of your sensors reading wrong.