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I have been running my SG for awhile now and am please with the results overall. However, I perplexed with the fuel offset adjustment and wish to gain as much accuracy as possible from my SG. Every time I fill up the offset factor needs to be changed and while my driving habits and routes do not vary substantially I find my economy varying. So I am asking the collective members of the site for input. I have included figures from my last fill ups to assist and possibly clarify the situation.

Odometer - 606.3 miles, 22.3 gal.
SG - 599 miles, 22.9 gal., 5.3% offset

Odometer - 507.8 miles, 18.8 gal.
SG - 502 miles, 19.6 gal., 4.5% offset

Odometer - 549.6 miles, 21.6 gal.
SG - 538 miles20.7 gal., 8.8% offset

Odometer - 533.6 miles, 19.7 gal.
SG - 500 miles, 20.8 gal., 3.9% offset

Odometer - 569.1 miles, 22.3 gal.
SG - 562 miles, forgot to note gallons, but ended up with an 11.1% offset

Good job recording the details. That us something to work with. When you say 5.3% offset, do you mean you had that offset for the duration of the tank, or that you selected it at the fillup at the end of that tank?

It looks like you need about a 1% Speed offset, to get the miles matching up. However, this won't affect the fuel usage readings at all.

I get a total of 84 sg gallons and 82.4 actual gallons (skipping the last one). That's a -2% fuel offset. All the offsets you listed above are in the same direction, so try moving it the other way (lower / negative offset).

Another way to handle pump variations is to only do a halfway offset adjustment. If the gauge says 22.9 gallons and the pump says 22.3, you do the fillup procedure with 22.6 gallons. It should approach accurate after a couple fills this way.

Are you filling up the same way each time? If you are topping off the same way you shouldn't be seeing that much swing. I only see that kind of movement with e-10 vs straight gas, do you know if your alcohol content is the same, winter formula will effect the adjustment too.

I used to do the same. each tank would have to change the adjustment and never would be close, so i started over and did like Andrew suggested. I'd change only half the adjustment the SG was showing and soon was seeing closer and closer numbers.

Thanks of for the great input! The offsets were made after I filled up in order to make the SG match the fuel registered on the pump. The fuel here in NW Indiana is 10% ethanol. I try to fill up at the same station and pump, facing the same direction. I set the pump handle on the lowest setting with the handle all the way in and remove it as soon as it clicks off. I started recording the info last September, I think we are now or will shortly be into using wiinter fuel.
goldie

You might try the 2nd or 3rd click, since sometimes the first click gets triggered prematurely.

Not sure if u already do this, but if u always fill up where the needle is at a quater tank, the scangauge seems to like that, and i found that it will be more accurate. This way u fill to about the same amount every time. Also i stop pumping when it clicks off the first time, because that's what works the best for mine.

Many thanks for all the useful comments! I usually fill up when I'm between 1/4 and 1/2 showing on my gauge. Now I will try to get closer to 1/4 of a tank when filling up, use the second or third setting on the pump handle, and incorporate the half way adjsutment of the SG as mentioned earlier. I have also made the 1% Speed offset as suggested. After few more tanks, I post my results. Again, thank you all for the assistance!
goldie

goldie, when i'd change mine it would go from 14.7 to 16.x if going up and if i changed down it would jump down to 13 or so. That was lil too much so i found that once i change whichever way i wanted I'd go back in and then it would change by .1 instead of big jumps.

I take a totally different approach regarding the SGII offset. I have a factory FCG that cannot be offset so after 12 tanks of gas I determined it was high on average 4% compared to pumped gas at fill-up. I don't change my SGII offset based on how many gallons I pump at fill-up. Instead, I compare my FCG and adjust my SGII offset and Fuel-cut to match -4% of my FCG. The problem with the SGII is the offset will not match -4% of the factory FCG until well into the tank of gas and near fill-up again.

Example - I set my SGII offset at 13% and at first it might be 13% lower than my FCG. As I continue adding miles that percentage reduces till I get to the end of the tank to match the -4% of the FCG. Every tank fill can be high or low so I need the gauges to be as consistent as possible to each other. Changing the SGII offset each time at fill-up would really mess things up with these high and low fills I get in my '09 FEH. I just base my mileage on all the gauges in front of me. After fill-up, I get a Miles To Empty reading in my information cluster. This will tell me if I had a low fill. Second, the gas gauge will tell me if I had a low or high fill depending on the miles it takes to start moving off of the full mark. As I get down close to 50 Miles To Empty the computer is constantly adjusting to -0- Miles to Empty. At -0- Miles To Empty I have .8 gallons left every time as a reserve. I determined this after running out of gas once and so I did it again to verify. So now I know based on the Miles To Empty, the gas gauge, the size of the tank, and the amount of gas I add at the pump if I got a low or high fill-up at the pump each time.

My SGII tank size setting never changes from 15 gallons so why would I change the offset adjustment once I got the true adjustment based on all of my other gauges? I will continue to get high and low fills so why chase them with an incorrect offset? With the SGII set with the most correct offset based on all the other gauges you have a better idea of what your tank MPG will be at fill-up and throughout the tank.

GaryG

I've kept a running total of SG un-offset gallons, and pump gallons. Now, I just set my scangauge to the difference between the two - with several years of data, that number never changes. I've learned by now that the SG is right and the pump is the source of variation. The result is good, too - this morning's fillup was off by only 0.5%.

Andrew - thanks for the great information. If I'm understanding this technique correctly; after filling up, I set the SG offset 1/2 way between what the pump registers and what the SG shows I've used since the last fill up.
goldie

Right. Then, if the next fill is off in the other direction, you're already halfway adjusted, instead of seesawing with huge offsets.

Andrew - Thank you and thanks to the rest you of who gave me their input. It looks like I'm on the right track. By the way, after setting my speed offset by 1, and trying some informal testing, it looks like that will be a big help. I'll post my overall results after another 6 or fill ups to give the SG a chance to "settle down".
goldie