MPG Calculation

[alexcm]

I drive a 2000 LeSabre that displays gas mileage. The display values are consistently above manual calculations. On a recent 2800 mile trip the display was 34-35 MPG(average value) and the manual calculation average over the entire trip was 31.6 MPG. I am quite happy with both numbers but why the difference? Does anyone know how the algorithm works?

alexcm

[tman]

Did you reset the digital fuel economy thing? When the average economy is displayed, hit the reset button, and it should be more accurate.

[Lesabrelover]

The owners manual states that the displayed average is for the last 25 miles traveled. That might explain why your overall average is lower.

[alexcm]

I did reset the average at the beginning of the trip. I monitored the average almost continuously during the trip and did not see any values outside of about 33.9 and 35.7. That is why I thought I should see my calculated value nearer than range.

Looking at the computer input list I don't see any direct measure of fuel flow rate. I suppose the flow rate is derived from other inputs.

[cLy_eLiz]

how do they measure fuel flow rate. is there any OBD software that can display the fuel flow rate/gas mileage in real time.