Hey everyone. It's been a while since I've posted on these forums. I used to be extremely active and life has led me astray. I'm still a Honda nut at heart.

I've got a stock 2000 Hatchback with about 155,000 miles on it. After driving to DC in my girlfriend's '07 civic getting ~37mpg I'm rather jealous. My hatch tends to average about 26-27mpg. I am measuring by checking the trip meter and dividing that number by the gallons I put in it on a fill up.

I have a prediction:

I'm quite sure my o2 sensors are original, I'm thinking replacing those alone will be a big help.

My air filter is a K&N which i keep clean. Stock airbox. My tires are factory size on factory steelies/hubcaps. My air pressure is fine in my tires. I drive pretty mildly.

My exhaust system however is a bit "interesting." It's a frankenstein mix of an EX header, new catalytic converter, some decent aftermarket piping, and a '06 SI muffler.


Can't think of anything else that would impact efficiency. Like I said, it's a stock hatchback with fresh oil and a lot of miles.

Suggestions?

 

Welcome back.

What condition are the plugs, wires, cap, and rotor? Is the ignition timing set to spec?

Any CEL codes?

Might you have an exhaust leak upstream or near the primary O2 sensor?

Is the engine running cold?

 

Wires and plugs are new. Rotor not sure, ignition timing as far as I know is fine.

No CEL

And the exhaust was just redone about a year ago. No leaks as I'm aware.

Engine runs normal temps.

Edit: Thanks for the WB

Excited to start re-learning what I can.

 

Make sure all of these are in good order before doing anything else.

 

Will do, thanks

Your thoughts on o2 sensor?

I've read before that some people, regardless of CEL, saw drastic improvements replacing their old o2 sensors.

 

Well, they'll probably go out pretty soon anyway, so you may as well try it. 26-27 MPGs is pretty bad for what car you have. I usually get low 30s in my 1997 coupe with about the same miles and it's on 205 series tires. When I used to live in North Carolina I could get up to 40+ fairly easily. Miami traffic kills me though.

 

Another thing, if you haven't done it in a while or ever, throw in some Lucas Oil fuel injector cleaner. It's good stuff and will only run you 5 bucks at most.

It's always helped my fuel mileage.

 

A bad O2 sensor can certainly reduce gas mileage. However, in the absence of CEL codes, I prefer first to focus on items that are more common causes of bad gas mileage (e.g., ignition system problems).