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Discussion Starter #1
I'm wondering what people are experiencing as far as the miles per gallon calculated by the trip computer versus actual miles driven divided by gallons to fill the tank.

My own experience is that the trip computer is ALWAYS on the optimistic side by about 1 to almost 2 mpg. It averages about 5% higher mileage than reality. It doesn't matter which gas station I fill up at (thinking that pump accuracy may vary a little bit, even though they are supposed to be calibrated and certified). It doesn't seem to matter if the mpg is the lower in-town variety, or highway miles. It's off by the same percentage either way. I'm pretty consistent in how full I get the tank, but I suspect most of the difference in how far it's off each time is due to that variability. Mine has never been "right on" or even pessimistic. I've seen a couple of other people report their trip computers are off in the pessimistic direction (real mileage is better than reported).

I think it would be great if this device had a calibration adjustment, but that doesn't appear to be the case. I've looked through the Helm factory service manual, but haven't found anything. It seems like something Acura could add as a feature to the trip computer calibration functions that can be accessed by pushing the right combo. of buttons, along with some of the GPS calibration functions.

I know it's just a gauge, but I'm an engineer and it bugs me to have it consistently "wrong," so that's why I'm asking about the experience of others who may be compulsive enough to calculate actual mileage. This isn't a serious "complaint."

FYI, my MDX is an '02, Touring/Nav. and I'll cross 8000 miles tomorrow. Average mpg over that distance is about 22 or a little less. Highway high is about 24 mpg. My usual mix of commuting and town driving is about 21. All-time low, about 18, but serious in-town short trip driving would bring it down below that. (People's definitions of city driving vary considerably depending on where they live and how they drive, so it's very difficult to compare mpg from one person to another).
 

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The readout is always off, sometimes as much as 1.5 mpg....when I fill up, I usually get anywhere from 17.1 mpg to 18.5 mpg by the trip computer with mixed freeway and street driving, but freeway never more than 10-15 miles at a time. I don't bother doing actual calculation anymore since I know the trip computer can't calculate correctly.
 

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Discussion Starter #4
Hockeyplayer - thanks for the link. I've been into that calibration screen on my navigation unit. Acura lets you adjust the accuracy of the temperature readout, and mess with the range-to-empty feature (basically changing what zero miles to empty really means), but apparently there is no correction factor for the mpg calculation. There's also a more obscure navigation GPS adjustment where you can apparently adjust how the car reacts to the GPS signals versus the car's own knowledge of how far the odometer says the car is travelling. I guess that would have an impact wherever the GPS signal is temporarily lost. The service manual says not to mess with that one, and leave it in the automatic mode. I don't think it would do any damage, it would just cause the GPS navigation to be less accurate. They call this adjustment something to do with a "tire" calibration. I was originally hoping it would affect the mpg readout (by changing the distance the car thinks it has travelled buy hopefully not messing with the actual odometer accuracy), but that's not the case.

I know that some BMW models allow this correction to be made, and others, like the newer 3 series, don't. With BMW, you can essentially input a correction like "times .95" or "times 1.05" or whatever you need.
 

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Hmmm. Thanks for the info Dale MDX. "Now I know......and knowing is half the battle." Stole that one from the ole' G.I. Joe cartoon.:)
 

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I have checked the accuracy of my trip computer a half a dozen times and it has been relatively accurate.

Actual MPG has been .1 to .5 less than the trip computer has indicated. The time it was .5 low was when I had to do a lot of idling when trying to get out of a busy parking lot. It has been closer on long trips without a lot of stop and go travel. Perhaps long stops while at idle effects the accuracy.

Although I can't find it I thought that there was an adjustment to calibrate the accuracy.
 
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