Well if you are on the brake and slowing you'd be using less fuel, so I'd assume the bars should go up.
If you'd be cruising at say 60mph and let off the gas the bars should go up also, I'd assume. I mean when you let off the gas you cut the fuel to a certain speed/gear. I know my car is a bit more archaic and runs a different ECU but in 5th gear if I let off the gas my injectors are shut off until I hit 47mph, similar in all other gears. So if a the instant mpg display is hooked up right it should read engine load (fuel trims and manifold vacuum (MAFS count)) and when you brake you create more vacuum and the injectors should shut off.

 

Well if you are on the brake and slowing you'd be using less fuel, so I'd assume the bars should go up.
If you'd be cruising at say 60mph and let off the gas the bars should go up also, I'd assume.

Yep i understand.. and that's exactly what happens when I'm set to MPG. When I change the units to the metric version L/km the exact opposite happens.

See the quirk?

MPG is the opposite measurement to L/km. So for example - for better fuel economy using MPG you want a higher number... but for better fuel economy with L/km you want a lower number. When Ford programmed the computer though they didn't take this into consideration - they just graphed the numbers directly.

When I'm set to the metric unit (L/km) and my fuel economy INCREASES.. I get less bars.

It's technically correct but totally counter intuitive - because in my head I want that graph to represent "fuel economy" in general - more bars should equal better fuel economy regardless of whether I'm set to MPG or L/KM.

My friend who drives a 2005 Mustang swears that his graph does not show this "quirk".

Just for clarification: L/KM is Litres per Kilometre (the reverse of Miles per Gallon). I might not be making a lot of sense becaus in the US your computer likely only shows MPG... but in Canada I can choose to change it between either MPG or L/KM

 

strictly speaking isn't the metric unit L/100 km?

where 8L/100km is roughly 30mi/gal.

 

Yep - correct.

But the graph just says "L/KM" and it sorta doesn't matter because there are no numbers on the graph - it's really just showing an indicator of "better" or "worse". When you change the computer to show the ACTUAL average gas mileage calculation it is showing it in L/100km as you mentioned.

 

I just bought a new Focus but I have always had mine set for MPG I will have to try it on metric and see what happens.

It really would not bother me because I plan on using MPG anyway

 

I personally don't like the measurement L/100KM either. I find it hard to reconcile in my head what it means. I much prefer MPG. The only problem with leaving it at MPG is the rest of the system also changes - odometer, temperature etc. And as a Canadian I want to see those in metric.