I don't know how the computer calculates MPG but I know it is not accurate. On my truck my computer shows on average 18mpg city and 22 hwy but by actual miles driven divided by gallons put into the tank I average 10mpg city and 14mpg hwy. And the dealer says that is normal, go figure. I also have the 23 gallon gas tank and it is a pain stopping at the gas station to fill up every 200 miles,

 

https://www.f150forum.com/f118/fix-i...inutes-421912/

 

Yours is exceptionally off, around 40%. Fix the fuel correction tables and you be where you want to be.

See post #4 above mine.

 

"The computer can easily calculate the amount of fuel delivered through the fuel injectors and it measures the distance traveled from the odometer and then calcs MPGs. Generally speaking the truck underestimates fuel consumption by about 8-10 percent. There is an easy way to adjust the fuel correction calcs if so interested to get the truck to display accuracy to 1-2%."

You know that makes sense at first. But then thinking about it I can't see the logic to it.
1. The fuel injectors are quite precise, no reason simple computer code cannot know exactly how much fuel has been consumed. Knowing that it's pretty simple to calculate mile/gallon.
2. I had a simple flow sensor on a 1972 Chevy Longhorn that was very accurate.
3. Milage then should be as accurate as the odometer is.
4. How could the way a person drives have any effect on the injectors? Just measure the flow.
5. Pretty hard to believe the computer in the truck can tell me where I am within a few feet, but can't measure fuel flow.
6. Why would any car company just estimate the amount of fuel used? Doesn't make much sense.
7. The truck mileage calculator might underestimate, but it's more likely by design than sloppy readings.

I guess if #4 can be answered I might understand better.

 

LOL if you drive with such a lead foot that you only get 10mpg then you deserve to stop every 200 miles to fill up. Wonder why you haven't adjusted the easy fule correction calcs. And I would really like to see your source that the onboard computer can be adjusted to 1 to 2% accuracy, especially since you haven't bothered.

Hells bells, I had a 1972 Chevy pickup with the 350 engine and it was the last vehicle I've owned that only got 10mpg, Empty, full pulling a load it didn't make much difference.

 

Thinking a bit further, those onboard fuel readings have to be very close to exactly correctly.
The EPA rates each model for its fuel economy and they measure the amount of fuel themselves. If the onboard computer is reading low especially 10-15 % low as some have said, the vehicle would beat the EPA's fuel economy ratings by the same amount.

Also if the readings are 10-15% low then lots of people would run out of gas often, since the same calculations are used to determine the amount of fuel left in the tank. 10 % of 28 gallons is 2.8 gallons. That's 50 miles or so. The range of an F-150 with a 28-gallon tank would be 50 miles less than indicated. With the 36 gallon tank that would be 65-70 miles.

It is physically impossible for the onboard fuel calculator to be reading low AND for the vehicle to get less than the EPA rated figures.

 

Your MPG is not normal. Either you drive very fast on the highway, 80?, or something is wrong.

 

1) Precise is relative. Each truck is not calibrated to perfection, these things rolls off the assembly line every minute. You have to account for tolerances in fuel pressure, fuel injector pulse width, etc. All these tolerances compound leading to inaccuracy when not individually tuned. Hell, you may have an out of spec injector that is causing this that would not cause any running issues.

3) The odometer is also only as accurate as the tolerance it is designed to. Tread depth affects miles registered for example.

4) there is no flow rate that measures the fuel consumption, its a calculation that is pretty close. For some reason yours is way off, why I dont know. Calcs are easier and cheaper to implement.

5) GPS is also a calculation that literally takes into account Einsteins general relativity theory to make the prediction of where you are in space and time. (not a joke this is a thing)

6)b/c its the easiest way to do fairly accurately. Just b/c you dont understand it doesnt make it wrong.

7)yes it is by design to err on the high side.

Ford rolls out 400k + of these vehicle a year, every single one cannot be perfect. They can be however within a certain acceptable tolerance. Yours is out of calibration or there is something else causing this and is easily fixable by following the procedure in post #4.

 

I don't have a lead foot and I drive the speed limit on the highway.

 

Then your truck has a problem. Or, you aren't hand calculating right, which seems unlikely. Miles driven divided by gallons used (fill up).

I have a lifetime mpg of just under 18 per computer. Hand calculated is within 0.5 to 1 on each tank. I get anywhere from 14 something to 17 local, depending on the season, and 18 to 20 highway depending on speed.

If you go to Fuelly, you will see an average of 16+. http://www.fuelly.com/car/ford/f-150...=&submodel_id=