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I have a 1989 hatch DX which is getting 22mpg instead of the 30-35 that it should be getting. I need a new fuel filter and air filter, which I know effects the mileage, but I doubt it'd be by that much. I also have after market wheels which are 15" instead of 13", but once again I feel like that wouldn't effect it so much. Everything else on the car is stock. Could I get some help trouble shooting the problem? I'd like to be able to spend a little less on gas per month... I don't know a whole lot about cars yet so I apologize if this is a dumb question, i'm just trying to learn and researching hasn't done me much good.

Thanks!

 
Rep Power: 174

Bigger wheels WILL affect your gas mileage. It's probably a combination of things though.
Definitely the fuel and air filters.
How old is your oil and filter? Dirty oil makes your engine work harder. Consider changing to synthetic or at least high mileage.
Spark plugs?
Oxygen sensor?
Tire pressure?
Alignment? Suspension?
Is your carburetor dirty (or throttle body if fuel injected)?
There are a ton of factors that can add up to crappy gas mileage.

 
Rep Power: 519

Low altitude spec car being operated at high altitude?

 
Rep Power: 174

Doing a lot of short trips instead of longer ones?

 
Rep Power: 519

....under ideal conditions....which very few real people ever get to drive in.

Have you ever, in the past, calculated that the car actually achieved gas mileage as high as you expect?