maemo.org - Talk - Carman feature request

Sorry to revive this thread, but I have found some interesting info on this page:

http://www.windmill.co.uk/obd.html#Fuel

In a nutshell:

Quote:

Most vehicles do not have a fuel flow sensor, therefore he used the Mass Air Flow (MAF) sensor and the Vehicle Speed Sensor (VSS) to calculate miles per gallon (MPG).
1. Mass Air Flow - The mass of Air in grams per second consumed.
2. Vehicle Speed Sensor - The actual speed of the vehicle.

Vehicles use the oxygen sensors to feedback data to the vehicle's electronic control module (ECM) and control the air to fuel ratio. This ratio is set at the chemically ideal value of 14.7 grams of air to every gram of gasoline. He could use the known values to convert the MAF to Gallons of fuel per hour (GPH) and then calculate miles per gallon (MPG).

Here are the steps to make the conversion:

Divide the MAF by 14.7 to get grams of fuel per second
Divide result by 454 to get Lbs fuel per second
Divide result by 6.701 Gals fuel per second
Multiply result by 3600 to get gallons per hour
The expression for GPH is: MAF * 0.0805
To calculate MPG divide the MPH by GPH.
The final expression for MPG will be: VSS * 7.718

hope this helps
Darko