Post your ScanGauge setup & Adjust %

[basslover911]

Mine is also really high, something like 10.5% or so...

Speed is +1

[Formula413]

Originally Posted by MetroMPG

I've had the SG2 set at +8.0% gallons for a while, but my fill today was way off: 7.83 gal actual vs. 8.82 shown on the SG. That's 12.6% high, which suggests I actually need a *negative* offset to be accurate.

The 12.6% error just means you have to lower the 8% a little, not that you have to subtract 12.6 percentage points. According to some simple math 7% should be right on if your fillup was accurate. 7% is actually what I have been using (I reported 5% earlier) and it has been pretty close.

[Funny]

2002 Toyota Corolla S - 1ZZFE 1.8L engine: 9.9%+ on the Scan Gauge I.
This number is from many tanks of gas, and I can confidently say that this mileage figure is within 0.2% of actual mileage, every time.

Am I seeing a trend on the ~10%+ line here, or is it just a coincidence?
Darin, we may have you calling Ron about this . This would give an overinflated figure, right? One too many six packs in me to think about even this low-order math... perhaps in the morning...

[MetroMPG]

I filled up again today, after a long trip (750 km), and using a +3.0% fuel offset, the SG was still reporting more fuel used (6.68 gal) than the pump read (6.33 gal).

The 12.6% error just means you have to lower the 8% a little, not that you have to subtract 12.6 percentage points. According to some simple math 7% should be right on if your fillup was accurate.

Are you sure about that? If I remove the 8% correction from the SG's calc for fuel consumed (8.82 gal., in post #10), then the un-corrected amount is 8.17 gallons (8.82 / 1.08). It's still higher than the actual fill amount of 7.83 gallons. Am I doing it wrong?

I'm going to drop it to 0% correction factor for tomorrow's leg of the trip. I'm still predicting it'll end up needing a negative correction.

I wonder why it has changed from a positive offset to a negative one.

[Formula413]

I think I had it wrong earlier. If you were using a correction factor of + 8% and the SGII reported 8.82 gallons used, that means that it actually thought you burned 8.17 gallons, and applied your chosen correction factor to come up with 8.82. So based on that you should be using a correction factor of - 4%, which is about what you estimated. So yeah, go with that. As to why the correction factor seems to change, that's a good question. Mine was pretty accurate at + 5%, now it seems to work best at + 7%. Perhaps it is seasonal, I.E. the SGII is unable to account for changes in air density from different temperatures? This wouldn't seem to make sense however since it has access to IAT data. Does anyone know exactly how the SGII comes up with it's fuel usage estimate?

[MetroMPG]

Originally Posted by Formula413

As to why the correction factor seems to change, that's a good question. ... Does anyone know exactly how the SGII comes up with it's fuel usage estimate?

Aha! I think your question solved the riddle.

The SG calculates fuel consumption based on air consumption, and extrapolates fuel use with a formula based mostly on stoichiometric air-fuel ratios.

But I've changed my driving style. I used to do a LOT of pulse & glide (P&G), but now I mostly drive with load (DWL). In the Metro, P&G consists of a lot of non-stoichiometric, open loop acceleration. DWL keeps me in closed-loop stoich mode almost all the time.

So, the ScanGauge probably didn't know what the rich burn rate was/is, and obviously it was guessing wrong. It was underestimating it, which is why the offset that worked best when I was doing lots of P&G was +8%.

Also: maybe Linear Logic updated the SG's formula between versions? I've also gone from SG1 to SG2 since I first figured out that +8% offset.

Anyone else upgraded and noticed any difference?

Good reason to use a MPGuino.

[PaleMelanesian]

1996 Civic DX (d16y7) manual 5
Fuel +8% (or +12% with e10)

P&G driving all the time.

[RH77]

Originally Posted by PaleMelanesian

(or +12% with e10)

That's an interesting observation that I didn't take into account. I'm sure the Winter-blend is now in effect, so the adjustment may be needed.

-Rick

[PaleMelanesian]

Wayne G has registered a similar effect between summer/winter gas. We have the same year-round here, but a few months ago we switched to (almost) all E10 instead of straight gas.

[guudasitgets]

**based on the pic, I wonder what car can get 7mpg at 129MPH!!?

This gets 16mpg at race speeds, usually averaging over 110mph