Computer MPG vs Hand Calc

[Littlefield82]

I've compared a few tanks and each time the computer reads 0.75 - 1.0 mpg better than what my hand calc shows. What is everyone else seeing? I have changed the tire size and updated it in FORScan but I've not been able to get the PCM Relearn to work so I'm wondering if that's why the computer is off or maybe it's off like in a lot of vehicles I've owned before.

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[UGADawg96]

I've never had a vehicle across many brands that the hand calc matched the computer. Most likely due to the computer probably can't read accurately to the gallon. It's close, but never the same.

 

[12Lariat21]

To be within 1 MPG of the computer is probably as good as you are you going to get. You need to consider that the computer is an algorithm based on an 'assumed' flow rate of the fuel injectors, and the 'assumed' miles traveled. All of these are variable, and cannot be accurately monitored/calculated.

Your MPG numbers are better used as a comparison number, or an indicator of how hard you are driving, not a true to life, exact number.

 

[Bryan Simon]

Takes about two minutes to adjust this.
hand calculate your mileage per fillup

divide that number by what the truck tells you you got.

Display shows 21.3
actual comes out to 19.6
19.6/21.3=.9201xxxx

access engineering mode ( I forgot how since I’ve done it—simple tho)
change fuel AFE BIAS setting to 920 ——it should be set to 1000 factory

there are a couple of videos posted around here that show you how


edited to correct area of engineering mode from DTE to AFE BIAS

 

[pkinneb]

I never hand calculate

Ultimately for me I just use mpg as a guide to whether its consistent or changing due to conditions weather speed etc.

 

[Littlefield82]

Takes about two minutes to adjust this.
hand calculate your mileage per fillup

divide that number by what the truck tells you you got.

Display shows 21.3
actual comes out to 19.6
19.6/21.3=.9201xxxx

access engineering mode ( I forgot how since I’ve done it—simple tho)
change fuel DTE setting to 920 ——it should be set to 1000 factory

there are a couple of videos posted around here that show you how

Thanks. I just did this today.

 

[Jus Cruisin]

I haven't hand calculated my mpg for years. I agree with @pkinneb . I do look at the LOM to see if there's anything out of the ordinary going on. But, it is what it is. I get to somewhere between a half /quarter tank and I swing by the gas station and fill up. After gassing up the boat (carries almost 350 gallons), the truck doesn't put much of a dent in the yearly gas budget. Yeah, the boat doesn't get 1 mpg.

 

[Littlefield82]

I haven't hand calculated my mpg for years. I agree with @pkinneb . I do look at the LOM to see if there's anything out of the ordinary going on. But, it is what it is. I get to somewhere between a half /quarter tank and I swing by the gas station and fill up. After gassing up the boat (carries almost 350 gallons), the truck doesn't put much of a dent in the yearly gas budget. Yeah, the boat doesn't get 1 mpg.

I hear ya. The truck is so new to me that I'm still paying attention to mpg but after a few more months I'll likely just get in an drive. My 2008 Acura MDX required premium and averaged 16-17 so either way I'm doing better (minus the huge truck payment).

 

[Pedaldude]

For my new truck I have been recording my refueling on Fuelly.com, which does the math for you.

before that I would nearly always do the math in my head when filling up and whether you care or not about MPG, it's good to keep track of your mileage because any significant changes in performance can be due to any number of things wrong with the vehicle.

My truck is getting between .5-.2 MPG worse than shown, so it's close enough for me to not fiddle with the engineering mode.

 

[Bandito]

Just for convenience, to get into Engineering Mode, simply hold down the OK button on the right side of the steering wheel and start the truck. The center display will indicate that you are in EM and you can release the OK button. A press on the up arrow will land you on the AFE BIAS (Average Fuel Economy Bias?) page where you can make your adjustment.

After one or two adjustments, I have always been able to get within .1 mpg of the hand-calculated value which means I know the truck is telling me the truth. Before this adjustment, the truck was 1.1 mpg optimistic.

 

[pkinneb]

Just for convenience, to get into Engineering Mode, simply hold down the OK button on the right side of the steering wheel and start the truck. The center display will indicate that you are in EM and you can release the OK button. A press on the up arrow will land you on the AFE BIAS (Average Fuel Economy Bias?) page where you can make your adjustment.

After one or two adjustments, I have always been able to get within .1 mpg of the hand-calculated value which means I know the truck is telling me the truth. Before this adjustment, the truck was 1.1 mpg optimistic.

Thanks! Great info.

 

[JerseyGlock]

I've compared a few tanks and each time the computer reads 0.75 - 1.0 mpg better than what my hand calc shows. What is everyone else seeing? I have changed the tire size and updated it in FORScan but I've not been able to get the PCM Relearn to work so I'm wondering if that's why the computer is off or maybe it's off like in a lot of vehicles I've owned before.

My hand calculations were between .5 to 1.5 mpg.

 

[Bryan Simon]

Just for convenience, to get into Engineering Mode, simply hold down the OK button on the right side of the steering wheel and start the truck. The center display will indicate that you are in EM and you can release the OK button. A press on the up arrow will land you on the AFE BIAS (Average Fuel Economy Bias?) page where you can make your adjustment.

After one or two adjustments, I have always been able to get within .1 mpg of the hand-calculated value which means I know the truck is telling me the truth. Before this adjustment, the truck was 1.1 mpg optimistic.

I‘ve had a few naps since I did this, and completely forgot how I got in there.

 

[toyko joe]

Takes about two minutes to adjust this.
hand calculate your mileage per fillup

divide that number by what the truck tells you you got.

Display shows 21.3
actual comes out to 19.6
19.6/21.3=.9201xxxx

access engineering mode ( I forgot how since I’ve done it—simple tho)
change fuel AFE BIAS setting to 920 ——it should be set to 1000 factory

there are a couple of videos posted around here that show you how


edited to correct area of engineering mode from DTE to AFE BIAS

I just did this, I had to take mine down to 906!!! needless to say our PowerBoost is the only vehicle I have owned that has gotten far worse MPG actual than what the window sticker posts. 19.6mpg combined, my 2018 EcoBoost 2.7L got 25.4mpg combined, not sure I made the right decision on this PowerBoost. I also need to see if there is any electrical connection issue, as the battery system always seems to need to be charged/charging, very little electric driving.

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