Does anyone know how this is actually calculating it's values? At first I thought it was the amount of fuel sent to the engine divided by the distance recorded in the trip.

I've now realised that it can't be. Last night I had half a tank of fuel left so I'd driven over 150miles. The dash display was showing 50.2mpg when I started the car. By the time I'd driven half a mile to a point where I had to stop it was down to 48.3mpg.

Okay so it's winter here and it'd be burning more fuel initially but I don't see how a half mile trip with full choke can be burn so much fuel that it has that much effect.

Now my maths skills are poor but the isn't the above implying that 0.3% of my trip caused a 4% drop in economy? That's crazy.

My current theory is that the consumption display must be a rolling average over a shorter distance. 10 miles perhaps.

As such it's an almost useless figure. You can't use it to adjust your throttle position and you can't use it to judge how well the engine is running.

 

If it doesn't read 0mpg when you stop, or double when you let off the throttle, then it's an average.

NA Fits don't have this display.

Assuming your version has an OBDII port, see the ScanGauge thread.

 

Well it's certainly an average then, just not over the entire trip. Oddly it does go to zero when reset the trip but quickly climbs back.

 

Mathematically -

150 miles @ 50.2 mpg = 2.988 gallons used.

150 miles @ 48.3 mph = 3.106 gallons used.

=

0.118 gallon used.

At full "choke", that is certainly possible.

 

Hmmm. Okay, I did say my maths was a bit poor. I'm still going to check it out the old way "fill-to-fill" though