Fuel consumption calculation

I assume it estimates how much fuel its squinting out each time an injection fires and based of speedometer makes the calculations.

Wouldn't think there's much you could do to make it more accurate unless your speedometer is off but then your calculation would be off to.

 

Don’t worry about the computer being off . It doesn’t actually measure the fuel flow. It is just an estimate. Some trucks are close, many can be out 20% or more.
Pen and paper is the only accurate calculation.

 

I have a brand new 2021 that's off all the time. If you idle much, or do a lot of city trucking it gets even worse. The only way to really measure is to hand calculate it when you fill up.

Just slapping a new bigger turbo on the engine is not going to necessarily increase mileage. There has to be tuning to go with it in the ECM. If that wasn't done correctly, the inputs the fuel mileage readout uses to display the mileage may be off by quite a bit.

 

Is it calculating in the fuel used at idle? It doesn't take much idling to knock the mileage way down.

 

My 99 Classic had the Detroit dash computer on it. It always read higher than actual. I heard it was based on RPM readings. Don’t really know how it works. I used it to refine driving habits. What I noticed is the higher the computer went, the more it lied. 7.5 was actually 7. 8.5 was 7.75, 10 was 9. I hauled very light loads, and got amazing fuel economy. It was a pre Lo Nox engine. It was interesting for a while. But got tiresome. Finally just started running it how I wanted to. Mileage settled in at around 6-6.5 for the life of the Truck.