Should Scangauge II Match Honda MPG?
 

Today was the first time I actually compared the average MPG of my Scangauge II and what the Fit says fuel economy was. Here's what I got.

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Not too terrible of a difference considering 2 miles per gallon on an 8 gallon fillup is only 16 miles difference, so about 6%.

But considering how the range is calculated, I had a much greater gap.

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The Scangauge II said I could go 50% farther than what the Fit was telling me. I understand that there can be differences by the way things are calculated, but the range difference is pretty big. I suspect I probably need to adjust the corrective percentage on the Scangauge the next time I fill up, but I do set the gallons to show what I put into the tank. Having the setup value set to 10.0 gallons, I would think the adjustment value should be 6%, since the tank is 10.6 gallons, but I think the adjustment is higher than that.

Has anyone seen similar differences between their Scangauge II and what the car is reporting?

i'm still only on my 2nd fillup since getting mine. distance is off by 1%. is ur odometer and the scangauge distance the same for u?

Good point! I actually forgot about distance. My distance is off by about 1.4% or 1.5%. I did submit a suggestion to Linear Logic to implement an adjustment value for distance similar to how the fuel tank is adjusted. I don't know if they'll ever add that, but I think it's pretty important. As far as I can tell, the only way to adjust distance is by adjusting the speed adjuster, but that's in whole percentages too, so being at 1.5 percent, I can't get an exact match.

I do really like having the water temperature gauge. I learned that with the MY'15 the cold engine lights winks out at 127 degrees Fahrenheit (52.7C), although I don't know what's significant about that temperature. And with my previous Corolla and this car, the fan set to full hot doesn't start to get to a cozy warm until at least 150F. I think having a newer car seems to warm up faster and does a better job of defrosting the windshield while still cold than my last car, too.

i'm off about 1 mph. My GPS would say i'll be at 66 mph, SG will say im 65-66...

You need to calibrate the ScanGauge for mileage and fuel every fillup until you're happy with it.

I followed the instructions, and the only setting that really seems open to interpretation is Cutoff, which is said to be 3-4 points above TPS at idle. My idle was around 12 or 14, I think, so I set it to 16 or 18, but the average MPG was pretty off so I adjusted it some more. I love the Scangauge for what it can display, but getting distance and MPG to seem accurate is more difficult than I expected. At the very least all average MPG per tank is relative, so I know if I had an exceptionally efficient tank or not.

FitCharlie, have you done any mods to your Fit to get such outstanding fuel economy? We have '13 Sport AT and '15 EX CVT and I don't think we see such high averages.

Every fillup, tweak the miles and fuel. It could be several tankfuls before the ScanGauge starts matching the odometer and the pump.

The first step to good mileage is good instrumentation, and you're already working on that. Inflate your tires to at least the sidewall pressure. After that, drive as if you don't have any brakes. Turning gas into brake dust isn't very useful. And in the future, stop buying cars with automatic transmissions. Being able to pick your gear and not have a computer or pressure sensor decide that it knows better than you is important- it also lets you explore Neutral, because engine braking is a waste of gas.

On my 2nd fill-up, the miles driven per my SG was 388 and per my odometer was 394.6, a difference of 1.7%. I adjusted my SG to +2% to mitigate the difference (I sure wish the adjustments were available in tenths and not full percentage points). I'll see what effect that has on my next fill-up. Charlie is correct though, it could take several tanks to tweak the SG.

Charlie, you mention that engine braking is a waste of gas. At times, I actually use engine braking (instead of my brakes) while slowing to keep my RPMs high enough to keep the engine in fuel cutoff mode. I guess I'm assuming the Fit has fuel cutoff, as most newer vehicles should. Does anyone know for sure if it does and at what rpm the fuel turns back on (it's usually between 1000-1500 rpms)? I have the fuel cutoff on my SG set at 24, not sure if that's correct, but because of that the SG reads 9999mpg during engine braking.

Cutoff is recommended at being +4 over idle TPS. For me, idle is 13, so I set it at 17. Linear logic also adds the caveat that you only need to adjust it if your estimated mpg seems inaccurate.

GoBucky- Engine braking is great when you want to use brakes, but elsewhere there are plenty of times when you don't need to be on the gas and don't want any brakes at all- engine or otherwise.

Agreed, I use engine braking, as opposed to using the brakes, when I need to slow down quickly. I also neutral coast often, and I have for years, on my automatic transmission equipped cars.

That's hard on an auto trans though. I'd never do a thing like that in a car I care about...

So is detriment to the auto trans possible with frequently shifting in and out neutral?

Its just a shock on the drivetrain, going from ~800 RPM to whatever crusing speed revs are.

I double checked my Scangauge calibration. Speed is +1%, cutoff is at 17. I made the time to compare a handheld GPS because it provides precision of speed to a tenth of a mile per hour. As best as I can tell, and there's definitely room for error, the Scangauge does not round up to the nearest mile per hour. So 54.5 mph won't show as 55 mph, you need to speed up to 55.0 before it shows 55 mph. With the adjustment of 1%, it isn't noticeable until about 58 or 59 mph. At 60 mph the Scangauge was receiving 59 mph for the OBD-II and +1% bumped it to 60. I'm still having trouble getting the fill up and range on the Scangauge to match the car. My MPG was close to the cars, but higher than the actual math.

Fuel Remaining
Car: 7 ticks (2.9 gal?) SG2: 4.5 gal. "Actual:" 4.65 gal

Fuel Economy
Car: 37.2 mpg SG2: 37 mpg Actual: 34.6 mpg

Range
Car: 108 mi. SG2: 166 mi. "Actual:" 161

Wow, I haven't done the math comparing all three methods of monitoring fuel use before. I'm surprised that despite the fill up differences on the Scangauge varying from the pump, the remaining fuel isn't too far off. I am surprised that the miles per gallon isn't closer to the actual. Perhaps that will be something play with the cutoff value so they match.

But wouldn't you rather have your SG match actual figures rather than the Fit's overstated numbers?

Yes, that's true. I was just kind of surprised on how one value seems to match the actual, but not the other. I'm hoping that in a few more full ups I'll have it tweaked.

i upped my speed calibration by 1% and now i'm within 1 mile of my Car Odo vs SG Odo.

In my correspondence with LinearLogic, they made it seem like the odometer difference is of no concern. They only stressed to make sure the speed on the Scangauge matched true speed. Even with a consumer grade GPSr it seems like there may be rounding errors between the speed on the GPSr and the SG. But I think 1% is good. Distance-wise, I think my SG is about 0.4% - 0.5% under the car odometer. Unless we regularly drove over 100 mph, I don't think the difference between 1% and 2% will be noticeable as far as speed matching is concerned.

My tank fill up yesterday was 6.665 gallons and the car reported 38.8 mpg and the Scangauge said 38.6 mpg. The pump calculated was 34.4. I increased the Scangauge Cutoff setting to 20 from 17. I guess I'll see if that makes a difference when I fill up again.

The Scangauge expected 6.5 gallons to be put in the tank, so I didn't change it. What I did last time I filled up though, was I immediately went through the full up steps again, before leaving the gas station. I set the fill up adjustment to 6%.

i just filled up today myself. not paying much attention to the mpgs comparison. my fillup today was 31.59 mpg, i think SG was reporting 33~ mpg. the tank was very close. i filled like 9.6, SG thought i used up 9 gallons. increased the calibration to say 9.3. now i think i can start seeing if things start matching up better. mileage on my odometer and the SG matches now too.

With my last fill (which was my third fill-up), SG said I used 8.9gal, I actually filled 9.1gal so I changed the SG to 9gal (I compromised since pump accuracy is a variable) which increased my fuel adjustment to 12% (from 10.9%). My SG miles were within 1.5mi of the odometer (I have a +2% speed adjustment). I'm getting close to having this thing tweaked. Oh, I also changed my Fuel Cutoff from 24 to 17 (I don't think that will have much of an effect, but I didn't want the SG to think it went to DFCO too early).

I filled up the tank yesterday, and the Scangauge was actually near perfect. I filled 7.596 gallons and the SG fillup expected 7.6 gallons. The fuel economy was pretty accurate too. my actual was 38.7 mpg and the SG reported 35.6mpg. I changed the cutoff when I filled up because it was higher than the car, which I was expecting to be above the actual, so I'll have to put it back where I had it. I think it was at 20.

Like you, my SG's estimated gallons to fill is pretty close to actual gallons filled, but my actual vs SG mpg figures are always a little off (like 1 mpg or so), but not as far off as yours (more than 3 mpg). My biggest issue now is that this dang weather, 5th coldest February in history, is no good for fuel efficiency. I'm really looking forward to some 30 degree days, maybe in March.

My distance calibration is spot on now. Only 1 mile off actual. Fuel was off by .2. Sg mpg reading was 30mpg. Actual was 29.6 or so. I think im there now for calibration.

Try to stick with the same pump until you feel like it's really nailed down.

Like you, I've got my distance down. I'm within 1-2 miles actual (odometer) vs. SG. My SG speed adjustment is +2%. To confirm what Charlie said, I have used the same pump every fill-up, with the car pointed in the same direction and filled it exactly the same (at this point, I add 1.5 gallons after the first nozzle auto-shutoff). As soon as my calibration is complete, I'm going to see if I can get 2 gallons in after shutoff. I am getting closer with each fill-up. However, I don't expect SG mpg to equal actual mpg every time, there are just too many variables.

Does it seem fair to assume that if the car calculates the range left, that you can use that to find out how much gas is left in the tank? So if the range was 100 miles with a 32 mpg trip average, then can we assume that there is 3.125 gallons left in the tank? I wonder if this would be a reasonable way to calculating how much gas is actually in the car when the gas tank gets filled up. The manual says the tank is 10.6 gallons, but I don't expect this includes the fuel in the filler line when the pump shuts off.

i do somewhat the same calculation you are doing. supposedly the E light will turn on when there is 1 gallon left, I've found out it can light up as early as 8.5-9 gallons of gas left. However, when my light comes on, I look at the average MPG and give me 30-34 miles left before I run out of gas. I don't want to risk being stuck on the side of the road waiting for AAA or walking to a gas station. I don't trust the miles left gauge.

In all my previous cars I always filled up gas by the trip odometer. I use the fuel gauge as a guide, but ultimately fill up every x miles. The last few cars it's been fill up at around 300 miles on regular blend and about 250 on winter blend.

Let's see. I had 275 for my range and and average of 34.4 mpg. So I should have had 7.994 gallons in the tank. The pump shut off at 2.853 gal. so I should have had 10.847 gallons when it shut off. Boy, now another data point to monitor for a while.

You can use this logic to determine approx how many gallons you have remaining, remember the "Range" miles are conservative, so using this philosophy should prevent you from running out of gas. Also, keep in mind that "Range" is a dynamic number and will change depending on how your mpg's are trending (e.g. if you are currently getting much higher mpg than your tank average, you may actually see your range increase).

Did my 5th fillup yesterday. It looks like I may be as close as I'm going to get with my SG calibration:
-10.615 gallons pumped, SG estimated 10.6
-Tank miles per odometer 472.3, SG tank miles 474
-MPG per dash 46.1; MPG per SG 44.8; MPG calculated 44.5

I adjusted my Speed calibration from +2% down to +1% so my SG MPG should hopefully be lower than the calculated MPG from now on. My miles will be just a little more out of sync but I'd rather have actual mpg be higher than my reading so I get a little bit of a good surprise when I fill. We'll see how close it is from here on out.