My car used to get around 20 mpg, which is alright. I do a lot of driving between school and work which are short trips but now my mpg is around 16. This pisses me off. I just recently replaced the whole exhaust system because the catalytic converter was plugged up and the car had no power. Then I was getting around 14 mpg and it hasn't gone up that much since, which I was really hoping it would. So I have a parts car and I was wondering if maybe an 02 sensor or something of that sort would help if I replaced it. Any ideas anyone? Thanks for all the help. Much obliged.