Hello, I am Danny.
Yes, I am sure having your defective catalytic converter will be causing you to get worse gas mileage/MPG. I am surprised your check engine light is not on. I would suggest replacing the catalytic converter to restore your vehicle's performance, get better gas mileage, and to be able to pass a smog check if applicable. Hope this helps and feel free to ask any questions if needed. Thanks for using 2CarPros.
Friday, July 27th, 2018 AT 3:16 AM