In the manual for the SG is explains that one should fill up twice at the same pump, and use the fillup command on the SG to "correct" the fuel level to match the pump reading. I've done this a few times and ended up with numbers USUALLY around 6% or so, though I've seen it go as high as 10% and as low as 2%. Incidentally 6% makes it match relatively well with the internal NAV for me....at least until it starts dropping points.

Because fuel pumps are NOT terribly accurate for when the shut off I've been working on getting a more accurate number by keeping my correction at 0.0% and recording the differences, and doing the math in excel, always fueling at the same pump for each interval. I've only had three fillups so far and my percentages appear to be 6.43, 5.68, and 6.84%. I'm not sure exactly what sensor the SG using for its fuel usage. But assuming most of our vehicles have engines and such with fairly tight tolerances I'd think this percentage should hold fairly well across FEH's (at least for the 05-07 models).

What % correction for fuel is everyone else out there using on their SG?

For those who find their NAV is always 3MPG high or so compared to your SG... what is your SG setting?

 

TeeSter — For what it's worth (since I'm a TCH not an FEH owner), I have found that a SG setting of around +5% seems to be about right for the TCH.

Stan

 

My correction is 1% on my 08 MMH.

 

Mine is ~+6% on my 08 FEH.

But how accurate is this reading? There are some nights when I get home from work I can have a trip AVG of 40+ Granted I top out at maybe 45-50mph and try to keep rpm <2k, once warmed up (about 2 miles into my 6 mile trip) I can EV a good bit, & if I feather foot one streach I can got a whole block on EV (that's a country block of 1 mile). So I can see where maybe a 35, but 40-45, 50 ?! Really?

Then the wife gets in, makes the same round trip in 10min each way vs my 20min, RPM's hitting 4k frequently and trip avg is 26-28

 

+10% with two different SG's over the last 12 months.

 

I'm at +7% right now (was around +9% this winter). The last few tanks have been about 1% lower MPG on the scanguage than calculated based on gallons added.

-- Rick

 

Its latched into the Engine and computer communications... I suspect, once calibrated its pretty accurate. 6miles is a pretty darn short trip. You can, under the right conditions, drive nearly half of that in EV... but you'd have to be really careful and go pretty slow. Essentially your MPG during those phases is infinite!

HUGE apparent fluctuations in gas mileage like you describe are entirely possibile on these short trips depending on driving style, wind speed and direction, uphill/downhill, drafting (intentional or otherwise), temperature, battery condition.... I have drives where I get really great MPG readings and then two days later on the same drive I can get a MUCH lower MPG on the same short trip.

In short... I think the SG is pretty darn accurate, and you need to talk to your wife --OR-- more likely for marital bliss.... bite your lip and just sob inside silently

 

Thanks... that seems to imply right around 6% is correct and I might be onto something here.

I think the actual % will be pretty darn consistent across vehicles, and I would guess it should be consistent throughout all seasons but not sure of that one, I hadn't thought about it.

I just want to get a good average number and fix it there. There is so much fluctuation on gas pump shutoffs that I think trying to MPG from the reading on the pump every time is very inaccurate, and setting this number from ONE pump reading is a mistake as well... enough averaging should get a pretty good number.

 

Well.. four tanks and the experiment is done I think.

Pump readings
8.621, 6.975, 7.799, 10.811

SG readings
8.1, 6.6, 7.3, 10.1

If I do the math I get a correction of 6.5% (or 6.6% depending on whether you average the totals or each value independently). Statistics says their is a 95% chance its between 7.18%, 5.82%.

Now.... this morning I set my SG correction to 6.6%. I've previously adjusted my SG speed setting to 1% using a GPS to determine how fast I was really going....

After all those adjustments I reset my SG and my NAV to zero... I drove 40 miles to work.... final reading on the scanguage was 32.6 and on the NAV it was 32.7.

My belief is if you don't run the NAV past its internal memory (1000 pts?). I think its Accurate and I think it matches the SG pretty darn well **IF** you've set your fuel adjustment accruately and not just based on one reading at the pump. At least thats on my FEH.

I think the NAVs don't run 1-2MPG high or I've got one that doesn't. I think it has more to do with the fuel pump shutoff being so inaccurate and using one point based on that pump shutoff to set your fuel adjustment on the SG.

 

I can tell you that I use the exact same pump and fill until I can see a little gas (splash) coming out the filler neck. I park in the same direction/spot at the pump and also shake the car and fill slowly to reduce air pockets in the tank. I'm pretty sure I get a near consistent fill level every time.

That said, my NAV has almost always been off by 1-2MPG when compared to hand calculations.

I don't have a Scanguage...yet.