Hi everyone!*I have a 07 4dr accord with 63000 miles, 4cyl, manual transmission. I am getting ridiculously poor gas mileage and I can't figure out why. At one point I have gotten close to 500 miles to a full tank of gas and now I'm only getting around 280-260. The only mods I have done is a muffler (which I also had when I was getting good gas mileage) a short ram intake (I've also put the factory intake on and had the same results) , and 17" motegi ff7 rims. The change has been gradual over the last year to year and a half. I have replaced the air filter and spark plugs. I have cleaned the egr valve. I have reset the ecu. I replaced the down stream o2 sencor. I change my oil regularly. I'm a little heavy on the gas pedal but I've always been that way. The check engine light is not on (except for when I replaced the o2 sensor). The engine sounds like it is running the way it should and always has... I just don't know what else to do. Please help if you can!!!

 

A lazy upstream O2 sensor can cause poor gas mileage without setting a code?