It depends on whether your car has a MAF sensor or not.
MAF Sensor:
MPG = (14.7 * 6.17 * 454 * VSS * 0.621371) / (3600 * MAF / 100)
= 710.7 * VSS / MAF
14.7 -
grams of air to 1 gram of gasoline - ideal air/fuel ratio
6.17 -
pounds per gallon - density of gasoline
4.54 -
grams per pound - conversion
VSS -
vehicle speed in kilometers per hour
0.621371 -
miles per hour/kilometers per hour - conversion
3600 -
seconds per hour - conversion
MAF -
mass air flow rate in 100 grams per second
100 -
to correct MAF to give grams per second
No MAF (Uses MAP and Absolute Temp to approximate MAF):
IMAP = RPM * MAP / IAT
MAF = (IMAP/120)*(VE/100)*(ED)*(MM)/(R)
MAP -
Manifold Absolute Pressure in kPa
IAT -
Intake Air Temperature in Kelvin
R -
Specific Gas Constant (8.314 JM/K)
MM -
Average molecular mass of air (28.97 g/M)
VE -
volumetric efficiency measured in percent
ED -
Engine Displacement in liters
This method requires tweaking of the VE for accuracy.
I have no idea if these are the methods the SGII uses. The accuracy will be off due to approximations (AFR ~14.7, etc). All the information is from the brilliant mind of
Bruce Lightner.
- LostCause