Problems with fuel economy - miles per tank
 

I just purchased a 2004 1-owner Civic EX Sedan about a month ago. 70K miles. Automatic. I love everything about this car, but have been very surprised at the poor fuel economy, as compared to what I was expecting.

Seems I am lucky to get 280-300 miles on my full tank at times. Is this normal? Also, what is the tank capacity? Sometimes I fill-up and am able to get more into the take, and other times, the pump cuts me off early. I am getting low to mid 20's mpg. I was expecting in the low 30's combined, and close to 40 on the highway.

I drive very much a mix of city and highway.

Thanks for your help.

Re: Problems with fuel economy - miles per tank
 

There should be no way you're getting under 30. You'll get less now than summer b/c of winter gas. Put in new quality spark plugs and change the air filter. If that doesn't work, maybe do a search for gearbox's forgotten tuneup mods

Re: Problems with fuel economy - miles per tank
 

What about oxygen sensor? How often does this need replacing?

Re: Problems with fuel economy - miles per tank
 

And you could put in a new O2 sensor since it's probably still the original but that's going to be pretty expensive since your car has a wideband instead of a normal sensor.

Re: Problems with fuel economy - miles per tank
 

Are you using cheap gas? It shouldn't make that big of a difference but along with other stuff like dirty air filter and bad plugs could cause under 30mpg.

Re: Problems with fuel economy - miles per tank
 

Fuel Injection cleaner may help too.

Re: Problems with fuel economy - miles per tank
 

I'm going to tag onto this thread because i don't see a purpose in making a new one. My car was getting 30-35 when i first bought it(i calculated by filling up the tank, running it, and then filling up and calculating miles driven / gallons of gas to fill back up) but now i am down to ~19 mpg. My driving habits have not changed, maybe a little less highway driving since i dont drive 60 miles a day for work anymore but still, i dont see how i would drop 10 + mpg.

I tuned up the car the day i bought it just because thats how i am with any used cars i buy. Only thing since then that i have done is cleaned the air filter(its got a k&n) and changed the oil. Plugs are gapped right, im using the same gas station almost every time, and im not getting any idiot lights so im confused. Tires are brand new as of when i bought the car and they are always at 30-35 psi.

I figured it would be my driving habits but seriously, i never accelerate over 3k unless i am getting on the highway and i take my time to brake. In fact my girlfriend even makes fun of me for it some times.

So im wondering, even without the CEL, should i change the o2 sensors? I read gearbox's post and to help you guys get my understanding i went to college(never finished because i changed colleges and degrees) for auto tech so i know most of the basics and concepts and theories and stuff. Any input would be great. Car has 115,5xx miles on it. Bought it with 110xxx miles.

Re: Problems with fuel economy - miles per tank
 

an old dirty oxygen sensor won't throw a cell only if the sensor completely fails will it throw a cell light. i just replaced my sensor with a oem denso that only cost me 90 dollars at advanced auto and thats the more expensive wide band.