MPG Calculation

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

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

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

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.

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