I have a 5 spd, 04 Accord EX. When I first bought it, I could get at least 400 miles out of every tank of gas, closer to 450 if it was mostly highway. Nowadays, I'm lucky to get 370 out of a highway tank. I've tried using higher octane, but saw no significant difference. Has anyone else seen or heard of this? Does anyone know what the problem could be?

 

do you perform regular maintenance and tune ups? How about your tire psi? I'm sure it's probably a bunch of little things.

Stick to that 87 though, you won't get better milage with higher octane.

 

Also check for dragging brakes...

 

milage on the car? milage decrease can be caused by failing o2 sensor and that usually does not trip a cel (check engine light)

 

How do you test your o2 sensor?