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Today I wanted to fine-calibrate my SGII. It does not give me credit for my idle-4'th gear-60mpg mode, and I realized that the instant mpg is way off at low speed.

The speed calibration is quite good, but to double check it, i reset the car's odometer and checked the amount of kilometers against the SG. It was very close, and I was able to fine-tune it one notch down.

So why not just forget about calibrating the speed? I mean, speed and distance are the same thing for the SG. It is just a series of pulses from a sensor in the gearbox Pulses/sec=speed, and number of pulses since last reset=distance.

So we can calibrate the speed of the SG to 3 digits precision by just logging enough miles/km's... When the distance is calibrated, you will find the speed is spot-on!

After doing this, I ended up adjusting the calibration in the fill-up screen 3% down and now I get similar results with iFCD and the SG at cruise speed, but I still think the SG has a rather large error at very low speed, maybe 10-20% too high...

Hi Shrek:

___As you have probably read before, the SG-II does not make up numbers but uses data from the OBD-II stream. If a VSS is off, it is off by the ECU, not the SG-II as 10 to 20% off it should never be. At least I have not seen it off by that much in anything I have driven.

___Do remember that in a FAS, until the OBD-II stream is back online and the VSS is reported, the SG-II is sitting there waiting for input while you are tooling down the road ICE-Off … If you are at any time under a FAS. Some vehicles are quicker than others to pick up the transition. Honda’s and Toyota’s can be wicked long wrt this. Ford’s are pretty darn quick surprisingly!

___Good Luck

___Wayne

Wayne, while I agree that the SG gets its info from the OBD stream... However, I have a digital Odometer in one vehicle and the SG's mileage is off by about 0.5% low. Now I know the speedo is off just by watching radar feedback. But, the odometer seems to be on. Unfortunately, I don't have a GPS to compare with.

For Shrek, depending on the vehicle, you can't rely all that much on the speedo. Both of my Toyotas read high. One seems to be off by a diminishing % the faster you go and the other is off by a pretty consistant +2 MPH. As for your calibration.... it is what I do and I agree with your method. I do manual MPG calcs and the ODO is what I use for that. So, I want the SG to mirror my manual calcs. So, I compare tank miles to my trip ODO.

Interesting. I too notice that my spedometer in my Toyota Echo is off by 1-2 MPH, although the odometer seems to be highly accurate.

I have a theory. The odometer is probably driven by digital data without the penalty of D-A convesion. On the other hand the Echo speedometer display seems to be a conventional analog meter movement, which probably means that a D-A conversion has taken place. In addition, the analog meters may be off calibration. Just a theory;)

Hi all!

I should mention that I am not so much interested in getting the SG to be perfectly calibrated when filling the tank. That is going to change with fuel quality etc. But I would like it to be calibrated against the car's computers, so that when I drive with the iFCD showing instant mileage on the convenient and clearly visible display in the radio, the average day/current trip average on the SG is correspoinding well.

(Of course I log my mileage based on the fillups and not on the SG)

Interesting. I too notice that my spedometer in my Toyota Echo is off by 1-2 MPH, although the odometer seems to be highly accurate.

I have a theory. The odometer is probably driven by digital data without the penalty of D-A convesion. On the other hand the Echo speedometer display seems to be a conventional analog meter movement, which probably means that a D-A conversion has taken place. In addition, the analog meters may be off calibration. Just a theory;)

I think it is simpler than that. Speedometers have always been calibrated low to account for variations so that they would never show too much even with seriously under-inflated tires etc.

I agree with Shrek. Most speedometers are spot on or read high; And I suspect that is intentional. You don't really want your customers comes after you when get caught speeding in a school zone when the speedometer said they were not.

Same here, my speedometer is ~2-3 miles faster than what the ScanGauge reports.