ScanGauge: How much calibration required on each tank?
 

I've been using my ScanGauge for a couple months now. After the initial calibration it has proved to be pretty accurate. My main complaint is the deviation from one tank to the next. It can be a pretty large difference. For example, one tank says I got 52 MPG but the gas pump says it was 48. I follow the procedure in the manual and offset the fuel usage to "calibrate" the ScanGauge. The next tank it might indicate 46 MPG, but according to the pump I got 50. According to the manual I should calibrate it every fill, so thats what I have been doing.

So I am just curious if this is common, and do you guys just deal with it? I've been thinking about just leaving the tank-to-tank calibration alone. Obviously making minor adjustments doesn't help the accuracy. It frustrates me because I think I'm getting 50 MPG but its only 46 or something. Maybe I should just leave it alone and not worry about it?

To get it to average out a little better you can calibrate it over 3 tanks or so. After that I'd just leave it. If its off a little its off a little. All the OEM guages are off a little (sometimes a lot). Its not an exact figure, just a real close guess.

Yes, average it out. The more tanks you average it over the better. Record the % correction required each time and average those.

One tip passed along here was to NOT enter the 'whole' error value, but only HALF of it, during each MPG re-calibration. That way your MPG values don't tend to oscillate between OVER & UNDER estimated values with each fillup. This technique "settled" my SGII readings quite quickly.

I thought I'd had mine dialed in for a while, but some tanks it seemed to miss the mark by a significant margin. I recently started tracking the scangauges amount and %correction with my fuel log because I think my sg can be off by +/- 5% depending on type of driving. For tanks that I spend entirely in town I seem to get worse than the sg shows, but for long trips I get better than the sg shows.

I wonder how much more accurate the MPGuino is? Can anyone chime in? I'm really not that concerned about accuracy, but it would be interesting to see if the MPGuino shows the variations that the SG does. Since the MPGuino uses a much more precise way to calculate MPG I suspect it is more accurate.

MPGuino, accurate once dialed in.

Almost the same problem here. I didn't get as much deviation, only a few tenths of a gallon, but one time I suddenly got about 2 gallons off. I've been recalibrating every fill up since and now its usually under by .2-.4 at most. I'd say that might be your cure... At least try it for a number of tanks and if it does get better then try leaving it.

I keep a spreadsheet and I can calculate my total offset since the start. If I use that and leave it, it's more accurate than any single pump fill.

The "adjust it only halfway" suggestion is excellent, though.

...FWIW, someone HERE suggested it first, not me, I just recalled & use it.