I bought the car in my sig about a month ago and it has been driving great, no hesitation or anything. But it has been getting like 17-20mpg. And I usually drive like a grandma with a good bit of coasting in neutral down hills. I have changed the plugs, wires, cap and rotor, air filter, the tires are 2 psi over. This car seems to coast miles longer than my old mazda so I don't think there is a rolling resistance issue. Treadwearlooks even. I ran a good injector cleaner for two tanks, the fuel filter hasnt been changed for a long time but it is located behind the brake cylinder and I can't get to it.

My best guesses so far are o2 sensors, cat converter, timing, transmission, fuel filter.

What do you guys think?

 

All of those items are good to check.

I would also say to make sure you don't have extra weight in the car by having a lot of heavy stuff stored in the trunk.

 

How are you calculating your MPG?

 

Also, how long are you warming it up???

 

Check the air filter.. in my last car it was dirty... changed it and I gained 1-2MPG no joke.. and these cars thrive on air.
If the Fuel filter has never been changed it is likely it is clogged or something of the nature, so definately get it changed. Jack it up and change it. The bolt may be rusted.. be wary because you may end up having to cut the fuel line-- take it to someone if that needs to happen if you can't do it confidently yourself.

 

To calculate, I hit the trip odometer every time i fill up, I divide the miles i drove between my last gas and divide it by how many gallons i just put in.

I usually let my car warm up about 1 minute, just long enough to put on my seatbelt, find a good cd, and adjust my floor mat.

Yeah, the fuel filter is usually one of the first things i change on a used car, who knows what kind of stuff the last owner used, but i can't seem to get to this one without taking apart the brakes. any ideas, maybe through the wheel well ?

 

My thoughts are if the fuel filter were clogged up the car would not be running well at all due to starvation especailly under load as in going up a long hill. Still a good idea for a new one but I question if that is causing the poor mileage.

 

Here is a link from the DIY section: https://www.hondaaccordforum.com/HOW...m_16788/tm.htm
You do NOT have to jack the car up to replace the fuel filter. Unless you like to work from the bottom (may be easier)

I doubt it's the fuel filter. the car would be running rough due to fuel starvation as RTexasF suggested.

 

I'm leaning towards something besides the fuel filter as well.... When you calculate the miles I assume that you fill the tank, reset the trip meter, then drive for a while, fill the car all the way back up and re-calculate?

Make sure that your trip meter is on par with your odometer. Next time, write down your odo number and work off that, try to use the same station/pump. Also, make sure you're using a good airfilter and NGK plugs, optimal shift point for fuel economy is between 3-4k rpm's

 

What about the o2 sensor? what other symtoms would that cause?