In addition, the car must have some way to determine how many gallons of fuel (or more likely, how many pounds of fuel) are left in the tank. Otherwise, the car's computer would not be able to estimate how far the car can go until the tank is empty. It can use this and the miles driven to determine average mileage.
Jeff
I'd like to know how they are calculating mpg just from ECU data. Makes me wonder how it can tell the mileage difference from say a
41 mpg Corolla, and a 27 mpg Chevy Impala for instance.. "actual real life ratings, I've driven both". The Impala had that mpg indicator built into the car on the headliner display. Seems to me you would have to calibrate the thing according to miles driven, and gallons of gas burned. They seem to let you input gas data. <JS>It's an easy matter to calculate the Injector ON time and the number of ON Cycles to arrive at how much fuel is in demand. The ECU knows how far the tires have gone, so figuring out how much gas was used to go how far is pretty easy.
</JS>
ALL of the data needed is in the ECU. Amount of fuel used gets calculated using the injector pulse timing, RPM, load percentage, throttle position, miles traveled and starting fuel load (calculated using the percentage in the tank) This get compared to a table in the ECU which it uses to determine mileage.
The reason you need to tell it the make/model is so that the machine knows which communication protocol to use. It then looks in it's memory and determines which code maps to use.
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