Around this time last year I purchased my automatic 08 Fit Sport with ~79k on it. I’ve put ~7k on it since, the two drivetrain recalls, two oil changes and basic maintenance (new Spark plugs, ignition coils, engine air filter, upstream 02, CV Axle and new suspension all around)

My gas mileage last year varied from 26 city to 34 highway, which wasn’t the absolute best but it was better than most. Fast forward to now, I’m lucky to see 24 and generally range from 18-22. I’m at half a tank with only 80 miles and I’m starting to become fed up. I’ve used many “tune up in a bottles”, changed driving habits along with replacing all the parts listed and I’ve had no luck.

I would highly appreciate any suggestions to bring this beautiful fit back to the condition it deserves🥸

 

There are two variable: you and the Fit. If your fuel efficiency dropped by 10 mpg something must have changed.

You mention that you've changed driving habits. I assume you mean that you're attempting to drive more efficiently, but since you've seen your typical mileage decline perhaps whatever you're doing isn't working. Tell us a bit more about your day-to-day driving patterns: how much city vs highway, how long are your typical drives, flat vs hilly, speeds, do you use cruise control, do you carry a lot of weight in the car, etc. Has any of that changed from when you were satisfied with your fuel efficiency to now?

One driving aid you might consider is a Scangauge or Ultragauge, which allow you to see real-time fuel efficiency and better learn how rpm, engine load, etc. affect fuel efficiency. Driving style definitely has a major effect on Fit efficiency. I can easily get 5 mpg more than my wife over a tank in the Fit, and I have a similar range advantage over her in our Nissan Leaf EV. She doesn't look ahead to plan for hills, roll to stop signs or lights, and she rides the brakes down any slope instead of using engine braking or just rolling.

You have done a lot of maintenance on your Fit, but one thing you didn't mention is a valve adjustment. If you don't have confirmation that the previous owner did it then it's time. Can you confirm that all the parts you replaced (e.g., spark plugs, air filter) are the correct part for a Fit? I think there are only two spark plugs recommended for the Fit (at least for my 2010) and from everything I've read you should definitely stick to those options. You also didn't say anything about the transmission, but it wouldn't hurt to do a fluid change.

You also mention suspension work. Did you get the car aligned afterwards and are you running stock size tires? Are those tires properly inflated (or even a bit above - many folks like 34-38 psi both for handling and efficiency).

It's likely that many different factors are playing a role in your poor fuel efficiency. I can't think of a single problem that will cause a 10 mpg drop, but if you need a valve adjustment, have a bad alignment and underinflated tires, are running the wrong spark plugs and ignition coils, and always drive around with your two buddies who play on the defensive line of the Bills, you will likely see a major reduction.

 

As said u forgot valve adjustment and tire psi. Did fuel quality change? Winter blend will give worse mpg (more ethanol) then summer.

did u change oil weight? Maybe check alignment, you hit potholes and now u r running too much toe.

There's a lot of variable to mpg, impossible for forum people to guess YOUR life.

 

Same issues here with a 2011. Bought this car new for daughter going off to college, now that she’s bought her own car-took the Fit back to use as an in town runabout. Was shocked that mpg which averaged 31-33 mpg last I knew, is now 23-25 mpg in mixed driving. Started by replacing filthy air filter. That immediately improved 2-3 mpg. Next move is new plugs and o2 sensor, lof and at fluid. Am I on the right track or is there something I’m missing. Car has new tires w proper inflation on it.

 

I've seen fuel consumption vary between 7.5l to 5.3 (31 to 44mpg) without significantly changing anything (like not towing a trailer or going 160 on the highway suddenly), I think the biggest factors are:

• Speed
• Ambient temperature
• Tire type & pressure

I'd control for that to see how it's working before doing anything, just go on a slow drive on a nice warm day and see if you're getting reasonable numbers.