Other than weight smaller wheels don't have much effect on mpg. Its the tire that counts most. weight and diameter and rolling resistance. And the wheel weight matters only a minority of concern.

 

Try removing the injectors and having them ultrasonically cleaned. It's a very complex test, spray pattern and pulse width are tuned perfect. I worked on Hornets in the NAVY and the fuel injectors patterns had to be perfect or you would get compressor stall. The perfect ratio fuel/air is 1/14.7. Trouble is it's not always a standard day 29.9 milibars pressure, 59% fahren, sea level , dew point etc. The mass air flow meter and the pre and post O2 sensors make the adjustments.

peace out

Brake Pad

 

Check the weight of the 205/45 and compare to your original tires on tirerack. Then compare diameters. if your new tires are heavier and larger in diameter you found the reason for reduced mieage, even after odometer reading correction.

 

I wanted to know if anyone has had a similar problem to mine and resolved the issue. I recently also noticed a mileage decrease.

At first I put 16x7 rota grid wheels, but right when I installed the wheels, one of the coil packs failed. So I replaced it, then I noticed my mileage wasn't the same. I assumed it was the wheels so I put the stocks back on.

Now that I have the stocks, I'm noticing that the mileage is still lower. I was getting 150 to half tank, now I'm almost at half and only at 110 mi. I'm not sure what it could be.

I'm not sure what could have affected the mileage, the coil pack went out on the freeway but only about 3 miles from home. It was new years so dealers were closed. I ended up using a coil pack replacement from o'reilly. I don't think the one coil pack would change the mpg that much.

Any input in appreciated.

 

I was noticing this as well. Mind you it was real cold and heavy city driving. One tank got me 300-329 another got me 400km. I usually get 500km in the nicer months. Weather is a factor. But 300km way to low. I went out bought fuel injector cleaner. Popped that in. Filled up full. I have noticed a difference. I intend to run fuel injector cleaner in my car once every 3-4 months now. Also you may want to look into doing a valve adjustment. I can't remember the last time it was done on my car. Used to be dealer serviced so by reviewing my bills I will know. But anyways, do a valve adjustment if you can. Not too hard do it yourself if you are willing and you should notice a difference.

Oh and stop hitting vTec lol. I know when I got the 300km tank I was ripping it hard. Late shifts and well being a speeder. Ferrari driver over here. And no I don't always drive like that. I represent people in traffic court. I've learned lessons through my clients lol. Even flooring it to the posted speed limit will guzzle gas quicker. 3000rpm shifts. Accelerate at a decent pace and do all the above, your mileage should go up. Unless you have a blown head gasket or something. But that you could tell.

I'm running stock tires, stock steelies, stock height.

 

There are several things at play
1. you should have measured the gallons to refill to your 'mark' at half full so you have good measurements. Just how accurate do you tthink that half full 'mark' is? the answer: not very.
2. Gasoline formulations change for winter and its not unusual for the gasoline to have less combustion energy in winter compared to summer.
3. Aftermarket coil packs have been a problem and could contribute to less mpg.
4. If the new tires/wheels were heavier than the OEM or bigger diameter you will see a drop in mpg.
We see on Fits about a 1 to 2 mpg drop in winter compared to summer and some of that is due to running at lower temeratures. Longer warmup and shorter runs at fully warm engines are the cause.

Trying to refill from any mark on the gauge simply doesn't work because the float position isn't that accurate and neither is the refill point unless the tank is topped off very precisely and thats not possible as some unmeasured amount will flow into the vapor recovery tank and screw that up too.
The ony reliable way is to refill the car to a known weight, measuring the weight of gas filled, convert to gallons and divide miles since refill to new refill and divide those miles by the gallons. The gallons must be found by accurately measuring the weight of gas that is used to refill in an accurate one gallon volume. Thats not going to happen with typical refills. ?The next best is averaging the calculated mpg over many refills.

 

-Well, I live in California so weather shouldn't be an issue.
-I've been going to the same gas station and using the same station # to get the most consistency and still noticed the lower mpg.
-I'm still seeing lower mpg with the stock tires back on.

I'll save up for a new set of oem coil packs. Is there a thread about aftermarket coil packs resulting in lower mpg? Can you post a link so I can research it? I just find it hard to believe because the car runs normal and drives the same with the aftermarket coil pack. That much drop in mpg for how it drives doesn't seem to make sense to me but I'd like to do more research.

Thanks for the input guys. Much appreciated

 

I also have 2008 Fit Sport MT which now has 228,000 on it. Beginning around the 60,000 mile point I began to notice a mpg decrease like you. I also began to get a misfire type of hesitation in lower RPM's with no code being thrown. After much diagnostics and talking with Honda, it was determined the fix is to replace the coil packs, plugs, wires, and adjust the valves. Immediately returned to 30 mpg range. Hope this helps.

 

Hello there,
Probably not what you want to hear, but I have the same issues with my 08 fit sport w/auto. The mileage just keeps slipping down. All maintenance has been done. In fact, I had the 105K service (valves, coolant, transmission fluid) done early at 96K to see if that was the issue and mileage did not improve at all! Only got 25.3 mpg on my last tank - awful. The car never got less than 31.5 mpg when new. Tires are standard size Goodyears. The one unknown on the car is the car was rear-ended doing major body damage two years ago. That probably didn't help matters! Otherwise, its been a great trouble-free car.

 

Unfortunately, since the output from refineries hasn't increased, gasoline companies are forced to increase the volume of gas at the expense of energy per gallon so most everybody is seeing poorer mpg. Not to the extent probably from 32 to 25 mpg. In that case I'd suspect the spark plugs and coil packs first. Thats a hard fact if you haven't changed plugs and paks in 100k miles. Another cause is the air filter; even apparently uncoated fiters can have enoughfiltrate to increase the loss in air flow to decrease mpg. So until there are new plugs, coil packs and air filters the mpg isn't properly determined. And then suspect the BTU per pound of gas. One more point: ckleaned your injectors regularly with injector cleaner? wally World sell good ones for about a $1 per and no ethanol content either. Ethanol content can also be a problem as it attracts water, creating acids that don't like fuel systems either. Supposedly less than 10% is Ok but then wonder why more than 10% isn't allowed. The difference between 9% and 11% isn't that safe.