Fixing overhead mpg numbers

[wildcoyote]

One thing I'm sure all of us have noticed is our overhead is off, compared to hand calculated mpg (mine is usually within 0.5mpg with lots of highway and little city).

The first thing that came to mind was the way it calculates this average. My guess would be, it takes the quantity (mm3/s) of fuel desired and averages that based on rpm and road speed. I believe the real fix, if you have your speedometer calibrated, is to address the fuel maps.

What is meant by this? Calibrate the fuel map (specifically, the duration table) to reflect the real amount of fuel being used (larger injectors would have to be compensated for). This requires custom tuning of course, but over the course of 2600 miles and three full tanks, I can say with some degree of certainty, this is the reason our overhead is off. I'm within .1 mpg depending on rounding to hand calculated numbers.

I tested it with a purposely off- calibrated map and saw a consistent 68 mpg over 100 miles on the overhead (I know I wasn't getting that LOL).

There it is, if you have questions or if this is in the wrong spot, feel free to move it mods.

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Sent from my SM-G930V using Tapatalk

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[Cummins7]

One thing I'm sure all of us have noticed is our overhead is off, compared to hand calculated mpg (mine is usually within 0.5mpg with lots of highway and little city).

The first thing that came to mind was the way it calculates this average. My guess would be, it takes the quantity (mm3/s) of fuel desired and averages that based on rpm and road speed. I believe the real fix, if you have your speedometer calibrated, is to address the fuel maps.

What is meant by this? Calibrate the fuel map (specifically, the duration table) to reflect the real amount of fuel being used (larger injectors would have to be compensated for). This requires custom tuning of course, but over the course of 2600 miles and three full tanks, I can say with some degree of certainty, this is the reason our overhead is off. I'm within .1 mpg depending on rounding to hand calculated numbers.

I tested it with a purposely off- calibrated map and saw a consistent 68 mpg over 100 miles on the overhead (I know I wasn't getting that LOL).

There it is, if you have questions or if this is in the wrong spot, feel free to move it mods.

Sent from my SM-G930V using Tapatalk

Sent from my SM-G930V using Tapatalk

I really appreciate you sharing this stuff when i have time to make another tune for my truck I may have a couple of questions.

Thanks again
Brandon

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[wildcoyote]

I really appreciate you sharing this stuff when i have time to make another tune for my truck I may have a couple of questions.

Thanks again
Brandon

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Feel free to ask!

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[Halojm]

I've corrected mine by running one size larger tires. Factory 285/60R20, put on 295/60R20 just that little bit bigger, my hand calcs are darn close to my overhead.

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