Average miles per gallon gage

[crispone]

I have studied this systems behavior quite a bit in my 68k miles with the '04. I have concluded that the "fuzzy logic" processor is taking into account a basic calculation that is based on the rate of fuel delivered (metered) into the motor as either a by-product relative to the TPS (Throttle Position Sensor) or the injector pulse count (duty cycle) and mileage driven (don't know if it is off the tranny, and ralative to tire diameter, etc... but I believe it IS and therefore affected by my larger tires with a CONSERTATIVE rate).

Since the system is calculating in this manner, the ACTUAL FUEL CONSUMPTION is not always reflected, since "transitional driving" (accelerating/coasting, etc...) will "skew" the value of fuel delivered.

Case in point:

Look at the "real time" fuel mileage metering from the OBC. You will notice that on FULL THROTTLE, your mileage is SHOWING a "pathetic" mileage level... in the single digits, even. Now COAST from a HIGH rate of speed... the OBC shows 99mpg... surely the UPPER LIMIT or threshold value it can "see". If this "REAL TIME" calculation is also the same formula that is tracking the AVERAGE over the entire distance... (very likely... as it is within the SAME electronic device, which would surely NOT use multiple inputs for calculation...) then you can "SEE" your mileage "improve" or "deteriorate" by holding a "steady" speed, and "subtley playing" with the relative throttle position and your "on/off" application and "coast" condition manipulation. There is a "happy position" of the throttle that can net VERY FAVORABLE mileage rates, that will BEAT your MANUAL (and MOST accurate) tank-to-tank calculations, and then there are driving manners that will show WORSE mileage on the OBC but net EQUAL or BETTER mileage in tank-to-tank driving tests.

SUMMARY:

The OBC is only a "reference", and MAY or MAY NOT reflect your actual mileage. My personal findings indicated an "optimistic" rate on the computer MOST of the time, but I HAVE actually achieved BETTER than 30MPG as well as BELOW 20mpg under very different driving across complete tanks of gas and compared both MANUALLY and ELECTRONICALLY... just because I was bored and curious.

All that matter is HOW MANY GALLONS you require to DRIVE AN ACTUAL DISTANCE. The "dashboard gizmo" is just flickering Liquid Crystal Display to help you "observe" your "relative" driving behavior as "seen" by the computer through whatever "inputs" (both less than "perfect", fuel consumption and miles travelled), and a close representation of the mileage you are possibly getting, with the added feature of seeing about how far you can still drive on the rest of your tank. (mostly superfluous features, but neat to the feedback-techie in us all...)


...but I could be wrong.


-crisp GUINNESS!

[Gadgetjq]

Is the average miles per gallon gage based off of the total amount of miles on the car or based on current diving conditions or both? How far back does it take into account? Can this be reset?
Thanks,

My experience (almost dead on during an extended highway trip and optimistic in general driving) seems about the same as other posts. That's led me to a conclusion.

The overall fuel mileage computation is only being done while the car is actually moving measuring miles and fuel burned. It doesn't seem like the system accounts for idling time when the car isn't moving. If I'm correct can throw the mileage way off if you do a lot of stop and go driving.

The overall mileage number will be kept until you reset it by pushing and holding the 'display' button on your steering wheel which resets it to zero (see your owners manual). If you don't reset for several tanks (or months for that matter) that overall number will change only slightly since you're working with a lot more miles. You can watch it vary quite a bit and rapidly when it's first reset.

Cheers