hey i have a 99 civic ex and i average about 250 miles per tank is that average or not? and if thats not what should i do to average more

 

Whats your driving like? i shift at no more than 3500rpm around town and got about 320 miles to the tank.

 

Depends on your driving habbits, as well as the condition of your engine's components, such as MAP sensor, O2 sensor, Fuel filter, your Air intake filter (how clean it is), spark plugs, ignition, motor oil, and a few others. All these things can help/hurt gas milage if kept well vs. Not maintaned correctly. The biggest contributors are O2 sensor and MAP sensor. When these two become worn and\or old, they dont deliver the right amount of information to your cars ECU, causing it to put more fuel in than necessary. Other than that, consistent general maintenance on those othere things listed will help keep your motor running good, giving you the best gas mileage possible.
ALso has to do with if you do allot of city driving vs highway driving. You use up more gas in stop and go, esp during any type of rush hour, when your more likely to get on the gas harder. When it comes down to it, it all has to do with what your doing with your right foot on throttle.