How accurate is the AVG MPG? Mine says I'm getting 39.9...those are 95% highway miles. Is this possible? If so, I like it!

2009 Fit (Base model, I guess)

 

That readout COULD be about 10-15% high. It's a known issue with 2009s & there's an engine ECU flash available from your dealer that will correct the false high reading.

The only question is whether or not it's already been done...

 

Mine reads a little high. I calculated 36.5 the car said 37.3, close enough for me.

I could see you getting close to 40 mpg doing all highway. I averaged slightly above that (car calculation) on a 1.5 hr highway run.

 

I know the AVG meter reading can be influenced by your driving style, especially right after filling up and being reset. When first reset, it becomes hyper-sensitive, changing widely depending on how heavy your foot is and how much coasting you do. The farther you drive, and at what speeds/throttle settings, greatly influences both that average displayed and fuel you will see burned. I believe this is influencing changes being made in the short and long-term fuel trims.

My last tank of city driving in 95F Florida with careful attention to my right foot got a horrible 26 mpg. The displayed average at the end was 29.5 (11.6%), not too accurate. I use Torque Pro and have set up dial/needle gauges to read avg MPG, fuel flow gal/hr, measured a/f ratio, MAF CFM, and cat temp. Easily visible, rapid, sensitive changes are seen, measured several times per second. The cat temp quickly rises as fuel is added. Also, the A/F ratio is maintained very tightly at 14.7, and you can see tiny rapid shifts of +/-.01 as the 02 sensor is working. Honda cuts the mixture to less than 29:1 in off-throttle coasting situations for ULEV ultra-lean burn, no burble or roughness, with seamless throttle tip-in response back up to 14.7. You can also see these changes reflected in fuel flow and cat temps.

Fuel flow shows almost instant change with the lightest change in throttle pressure. I was seeing 2.0 GPH cruising level @ 70 with windows up, A/C on. The dash meter wouldn't get above 29.9. After filling up with the same gas (Shell top tier 87) and driving the same trip the fuel trims and avg's began to swing up until I was eventually seeing around 38.5. The displays in Torque reflected a noticeably reduced fuel flow @ 1.7 GPH (15%), with it's avg at about 35 mpg. So there are a lot of adaptive changes happening in real time here.

 

So I calculated my tank when I filled up again on an app that I downloaded. It show 34.6 if I remember correctly. The AVG MPG in the car indicated 38.2.

I'm a brand new fit owner so bear with me. The AVG MPG is the average per THAT tank correct?

 

I reset your Trip A every time I fill-up and the computer will calculate for that tank. If I was going on a road trip needing multiple fills (and I haven't yet) I would track the trip with Trip B and just compute MPG it manually. Don't know what others do.

 

I thought fits only have trip A

 

Well, the question here is: how does the MPG readout know that you've filled the tank, so it can reset itself? It doesn't. You have to reset it manually.

This is done by resetting the trip odometer: push the button/stalk at the bottom of the instrument panel to cycle through to the trip reading, then push-and-hold until the trip display goes to zero. Every time you reset the trip odometer, the AVG MPG is reset as well.

If you want per-tank averages, you'll need to reset every time you fill up. Or, you can leave it alone and get a long-term running average over many tanks/weeks/months. Your choice.

BTW, that significant a difference between the readout and your calculation - right around 10% - suggests that the engine ECU reflash has NOT been done on your car. If you do get it done, you should see the readout drop down closer to your calculations.

 

Had to look in the manual just to make sure I wasn't imagining - yup, page 83-4 has Trip B gauge but now that I reread OP's post I notice he has a 2009 which might not have Trip B. My manual is for a 2015. D'oh!

 

Spot on. 2009s and 2010s only have the one trip gauge. Don't know about later GEs.

 

2012 only has one

 

I have a 13 but calculated both by trip reset and math. The computer was .1 off from my calculations.

 

My 2009 Sport (with the ECU Flash done) used to read about 4-5mpg high. I was seeing 45+ mpg on the trip meter from time to time. After the ECU Flash, I'm now down to about 1-2mpg higher than actual calculated mileage. It's better but still not great. I've had maybe 4-5 fill-ups where the onboard economy meter has been lower than my calculated... over 65,000+ miles (or about 2% of the time the car reads lower than actual). They still didn't get the economy meter flash update to the ECU right - but like I said, it's better.

I average about 32-35mpg right now. on an 800+mile (round trip) road trip over the 4th of july weekend, I averaged around 34.5mpg from VT to PA, (Windows Cracked, and speed around 72; meter was just under 36) and 32.75 on the return trip (A/C on and speed maybe a little higher ~75; Meter was around 34mpg). Driving on Country roads here in VT (as long as it is more than my 2.5mile commute to work) usually nets me around 38mpg (calculated).

I'm in agreement that the ECU Flash probably hasn't been performed. If that hasn't been done, you may also want to verify that the Lost Motion Spring Recall (which may apply to you) has also been performed.

~SB

 

My '13 Fit Sport is showing 23.5 mpg almost exclusively city driving and crossing the highest elevation point on the Eastern Seaboard to get to/from work every day.

I don't get it...my CRV gets better mileage than the Fit driving the same route.

 

and in New York and small ass engine = poor city MPG

 

I keep track of my 2012 Fit Sport AT's mpg on Fuelly. I also always include a note about what mpg the on board computer calculated. With a few of the latest fill ups, the trip computer has been conservative by about 1 mpg. However, the larger trend is that the computer is about 1 mpg too high.

Vincenzo (Honda Fit) | Fuelly

 

That's got more to do with what the word average means than with the ECU changing the car's tune based on the amount of fuel in the tank. 10 seconds WOT makes up a whole lot more of your average in the first mile after resetting your trip meter than it will a week later. This should hold true whether you reset the meter right after a fill or at 1/4 tank.

If you're noticing "the A/F ratio is maintained very tightly at 14.7" but seeing big changes in GPH, I'd account for that with another bit you noticed, "Fuel flow shows almost instant change with the lightest change in throttle pressure." Throttle pressure, outside temperature, load due to weight, gearing, slope, wind, traffic and other conditions have a lot more to say about your mileage than "careful attention to my right foot..."

How you use the car is a lot more important than how you use the throttle: If you're not driving the car smoothly and if you find yourself touching the brakes at times you're not coming to a complete stop, who cares about your throttle usage? The most gentle throttle application can't overcome an inefficient driving style! Pay less attention to the sudden changes in GPH from throttle pressure- in fact, stop paying attention to GPH for a while and pay attention to the brakes. Look outside the car and see what you're asking the car to do. Look and think ahead to conserve its momentum.

 

my Scangauge, onboard MPG meter and calculations are spot on. Strange though how my Scangauge never goes 9999 anymore. My average keeps going up this summer maybe because it has been very mild. My last 10 fill up average is nice!

 

my 2013 gauge says i get 34.4 mpg but fuelly records me as 32
I do mostly city driving