MPG decreasing!?

[enjikari]

When I bought my 2003 Sunfire used, it had ~41k miles on it. I'm a little over ~110k now. When I first bought the car, I could get ~320-330 miles before I would fill up (a little under a quarter tank left). Nowadays, I'm seeing ~250-260 miles on the same fill-up point. What gives? I heard that fuel filters are the cause of this, so I changed mine about 5 months ago. No improvement. Why does my MPG keep dropping? What can I do to reverse/fix/STOP this?

 

[oil country]

have u done the normal tune up stuff.....plugs air filter and yes the fuel filter....and are u driving eaxactly the same route u used to or has ur driving habits changed....are u using the ac all the time now???????

i have a 03 2dr 5spd and get 800kms per tanks and have had the car three yrs now with no complaints and i do regular maintanence

 

[enjikari]

have u done the normal tune up stuff.....plugs air filter and yes the fuel filter....and are u driving eaxactly the same route u used to or has ur driving habits changed....are u using the ac all the time now???????

i have a 03 2dr 5spd and get 800kms per tanks and have had the car three yrs now with no complaints and i do regular maintanence

I've had one tune up, I have regular oil changes @ every 3k, every 3rd oil change I also change the airfilter, changed the fuel filter once, my driving habits are roughly the same, and I don't use the AC any more than I normally have.

 

[djphuze]

Have you checked the tire pressures? Improperly inflated tires would cause a decrease of MPG.

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[Zimgxp]

O2 sensor, or coolant temp. sensor?