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Old 08-24-2012, 11:42 PM   #11
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The computer generated mpg always seems optimistic compared to hand calculated. Has anyone ever had the computer indicate worse mpg than the hand calculated number...I've never see it!

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Old 08-25-2012, 01:42 AM   #12
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I have had 2 occasions where the puter was 1/10th lower than hand calculated.....im not sure how tge new fords data mine, but i get average, instant, and last 5 min graph type readout......i have never had it off more than 3/10ths vs hand calculated......im happy with that !....of course if i reset it while slowing down i can get 99mpg......lol
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Old 08-25-2012, 08:26 AM   #13
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Quote:
Originally Posted by windrider View Post
Since there is no actual fuel flow meter on any factory truck, the computer readings are useless, and usually off 2 mpg or more.
Sorry, but my DIC is always within 1/2 mpg of my hand calc.
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Old 08-25-2012, 08:53 AM   #14
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I don't think anyone in the general public knows what all the formulas the computer is using to calculate mileage, closely guarded trade secret. Yes the fuel gauge comes to play, Mass Air Flow, throttle position, O2 sensors, (rich or lean), intake vacuum, transmission gear, torque converter lock up, outside air temp, coolant temp, and others sensor readings come to play. They probably do dyno runs, ant various rpm and load, and measure fuel mileage at several points. Then they can make a graph, plot the curve, then go work on all the formulas to get somewhat close to real world. I haven't owned a vehicle in a few years with a computer readout, but Dad's 2009 Explorer is reasonably close, a little higher than actual. May be due to wind, as I'm sure the wind tunnel test give drag coefficient and that is in the formula also. Of course extra wind would drop mileage. As you can see, the formula starts to get rather lengthy, with a lot of changing data. Glad to hear they are making it closer to real life.
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Old 08-25-2012, 12:16 PM   #15
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I dunno how it works, but it does......+/- 3/10ths in my case?....towing, hwy, idling, all pretty accurate...with all the sensors and computing power in these new things, its not terribly surprising....
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Old 08-25-2012, 01:08 PM   #16
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My 06 Chev truck was .3 optimistic when it was new, last check in 09 it was .2 optimistic. My 08 Taurus was .2 optimistic when new, last fall was off by 1.5 mpg (optimistic). This summer its reading about .2 low. The truck always takes more fuel than it says it burned.
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Old 08-25-2012, 06:49 PM   #17
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Going downhill, it cuts back to 4 cylinders and I get 99 mpg. You'd think running down to the beach I'd get at least 50 mpg!
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Old 08-25-2012, 07:39 PM   #18
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Isn't the fuel injection system fed by a constant displacement pump? That means that fuel flow rate is known as long as pump speed is known. Easy.
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Old 08-25-2012, 10:42 PM   #19
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Originally Posted by blw2 View Post
Isn't the fuel injection system fed by a constant displacement pump? That means that fuel flow rate is known as long as pump speed is known. Easy.
The fuel pump maintains the required fuel pressure needed for the injectors. The injectors determine the flow, not the pump.

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Old 08-26-2012, 07:51 AM   #20
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In my case, I use a ScanGauge II. The mileage differences can be adjusted with the ScanGauge. I keep a spread sheet of actual vs. computer mileage so I can get a good average over time, and have already made several adjustments to the ScanGauge since I got it. It might due for another adjustment, although it seems to be pretty accurate with my non-towing mileages. Here are my results from the trip pulling my Surveyor to the FROG Rally and back:

A low of 9.1 mpg (actual) vs. 9.6 mpg (ScanGauge) in the mountains of WVa. and eastern KY…..there were some long, hard pulls on that section of I-64. High was 11.7 mpg (actual) vs. 12.1 mpg (ScanGauge) for a section of mainly 2 lane road through rolling hills, with some stop and go in small towns and getting lost in downtown Winchester, VA. Overall, I had a 10.2 mpg (actual) average, vs. a 10.5 mpg (ScanGauge) average. Yep….the Scan Gauge is due for a little adjustment.
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