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  #1  
Old 08-08-2013, 05:14 PM
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Crazy mpg problem/ question

Got a wild question for you....somebody smarter than I am regarding these computers.

attached is a pdf file showing my most recent fillup. I have noticed on two recent road trips that if you go by the mile markers on the highway then my trip meter on the truck is somewhere around 20% off. If I drive a mile then it shows I have driven .8 or .82 of a mile which means as the sheet shows if I drive 400 miles then I really drove 480 miles. This would be irrelevant as to what speed you were driving. If I follow my speedometer then it is off by 7% roughly. So the question is per the spreadsheet which is the correct mpg for the truck. It seems to me that the mile marker vs the trip meter is the most accurate measurement divided by the actual fuel put in the tank. this also means my truck gets excellent mpg with 37" tires on it

Ford Mpg Calculation sheet


Trip meter
Gauge Actual %
0.832 mile 1 mile 1.201923077


Last Tank 389 miles 467.5480769 miles

Gallons 23 23

MPG 16.91304348 20.32817726

Speedometer

Gauge Actual %
70 mph 75 mph 1.071428571


Last Tank 389 miles 416.7857143

Gallons 23 23

MPG 16.91304348 18.12111801
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Old 08-08-2013, 05:22 PM
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I would use an after Markey GPS
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Old 08-08-2013, 05:39 PM
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Not sure what aftermaket gps is going to do. I am pretty sure the hwy dpt mile markers are accurate enough over 300 miles that can get close enough

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Old 08-08-2013, 07:08 PM
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Highway department employees don't get paid much money… if you want it to be dead on accurate go off of a GPS


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Old 08-09-2013, 04:31 AM
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Quote:
Originally Posted by Gburow View Post
Highway department employees don't get paid much money… if you want it to be dead on accurate go off of a GPS


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because GPS is so accurate.


want to be accurate and see how far your odo and speedo are off? go measure off 1/4, 1/2, 1, and 2 miles.

then see what your gauge reads compared to those markers.
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Old 08-09-2013, 04:59 AM
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Have you recalibrated your speedo for the bigger tires?
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Old 08-09-2013, 05:45 AM
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Just a few days ago, I learned that my SCT SF3 tuner will re-calibrate my speedometer to adjust for my 35" tires. It was always off by about 4 mph.

It now tracks perfectly and my mpg have increased all because it is taking into account the fact that I am driving farther than it thought I was driving between fill-lups.

I track my mpg religiously on fuelly.com. It is free and every drop of fuel I put in my truck is tracked on this site. Check it out!

Here is the link to my trucks MPG stats
2007 F-350 (Ford F-350 Super Duty) | Fuelly

Lastly, there is a free app called "Speedo HD" that is a speedometer.
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Old 08-09-2013, 05:51 AM
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I use to use that site for my DD. I haven't done it with my truck yet, but I still check my mpg every fill up.
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Old 08-09-2013, 05:47 PM
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I checked today based on GPS and trip calculator on truck is off by 17-19%

You cannot adjust the speedometer on the 11 for the 37" tires yet as far as I know. My speedometer is off by 5-6 mph at 70 mph. I am not sure that everyone follows my point. I have used fuelly on my 08 and some on my 11 but it is not giving you an accurate determination of your mpg due to the trip meter being inaccurate.

I am happy that it is getting better mileage than I thought I was


The biggest issue with using a GPS to measure the trip distance would be consistent accuracy of the GPS across 400 miles of driving during a week. The fluctuation of the GPS due to trees and everything else makes it slightly inaccurate for measuring this way. I am checking on interstate where it is clear and I know I it is as accurate as its going to get.

According to my math ford warrantied my truck bumper to bumper for 40,000 to 42,000 miles vs 36,000 per odometer


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Old 08-16-2013, 04:20 AM
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I checked my odometer the other day with my handheld GPS. I had acquired 13 satellites and it showed an accuracy of +-27 feet. Over a 20 mile trip to work it was .30 miles off. My truck said I went 20 miles exactly, my GPS said 20.3. Also my GPS said I was going 73 mph when I had cruise set at 75. It was off 2 mph across the board, well up to 75 anyhow.

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