I have been trying at times to get increased mileage just to see how high I can go. For a couple of days I was above 40 mpg. The first day it was 42.4 then it fell to 41.2 then it went down to 40 then eventually to 33.3 where I always seem to wind up. I drive 25 miles one way to work, about 5 in town and the rest on an interstate so this is mostly combined city and highway.

Anyway to the point of this. I sometimes view the instant or current gas mileage. I see it go way up on the downhill and way down on the up hill. This got me to wondering how it was calculated. Do they use engine rpm to figure how much is being used at any particular time? It seems to me that rpm biased by throttle opening would be a reasonably accurate way to get instant gas mileage. After all every rpm you should intake a fixed amount of gas, varying possibly with throttle opening as that changes the amout of air available. I have been searching the www but have not found any mention of this. I expect that I am just searching in the wrong places or using the wrong terminology. Does anyone know the answer?

 

probably based on current speed versus gallons per hour consumed to guess the instant mpg.

 

They use the pulse width of the injectors from the ECU and the RPM to measure the amount of fuel being burned then add the speed in to get the MPG. Seems to be pretty accurate from what I see with my Scangauge.

 

Thanks for the reply. That certainly makes sense to me. Where in the world did you get this information?

 

Pretty common knowledge in the GasSavers.org chat group.