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mdspadeccom
01-10-2011, 02:44 PM
Our new F10 repeats a display anomoly that I have also observed on all the other BMWs I have ever owner, namily that the MPG display goes to infinity whenever the car stops. Since miles per gallon is just MPH divided by GPH, and at MPH= 0 the MPG would compute to 0 as well, the logical thing is for the mpg display to show 0 whenthe car is stopped. Does anyoe know why BMW went to the extra efforts to make it do something else?

B-1 Pilot
01-10-2011, 03:22 PM
you are looking at the instantaneous sensor, not the average MPG over time right?

Ok so it would be 2 rates multiplied... usage of gas per unit of time, and distance travelled per unit of time (or speed). When either of these approach their limits (minuscule use on one side or very high speed on the other), the ratio will go very high. What you point out about coming to a stop is technically true, but when your engine goes to such a small demand as idle / coast or stop does even with a very very slow speeds you still will technically show 99.9 MPG. Finally i **believe** transmission or clutch come into play on this -- otherwise idling for extended times would be reflected in your overall average, which it isn't. Ask the guy who ran his car for four hours, the gas was gone but his avg. MPG was probably about the same. I first figured this about BMW computers on their bikes not their cars.

Also keep in mind efficient dynamics... I don't know enough about how the whole alternator to generator works to convert engine braking or whatnot to power, but this may give you less than accurate readings at anything out side of normal power settings.

Big picture, the instantaneous calculations that the BC does are only really accurate when moving at driving speeds.

mdspadeccom
01-10-2011, 03:32 PM
Yes, I mean the instantaneous reading, not the average. My point simply was that the "no brainer" behavior that you get from the obvious implementation of this indicator would have the MPG reading go to zero when the car stops. Note that when you are slowing down with the accelerator released you also have minimum feul flow, but the mpg indicator tracks the correct value all the way down to below 5 mph. It is only whne it approaches 0 mph that it jumps to infinity.

markl53
01-10-2011, 04:42 PM
Actually I'm pretty sure my previous 330i and 335i with mechanical instantaneous mpg meters would tend to go very high just before a full stop, then go back to zero when stopped. I have noticed that my F10 meter goes to max during a stop.

Emilner
01-10-2011, 07:43 PM
Yep, it makes no sense. It should be at zero when stopped. I do find the onboard average MPG to be extremely accurate. I reset it every tankful and have not been more than .1-.2 off....

CC Brown
01-11-2011, 04:57 PM
I find the computer MPG to be off from 1 to 2 mpg and it is always high. I drove to NC and though I was getting 32 mpg but when I filled up it was just 30MPH. I check every fill up and it is always high!

AzNMpower32
01-11-2011, 05:47 PM
The reason the newer digital display shows infinity during a stop is simply because of a conversion factor and the way fuel consumption is measured.

In most countries (EU, Canada), fuel consumption is measured in l/100km (amount of fuel consumed in a given distance. See here (http://www.treffbilder.de/93747769img_1143wuw-jpg.html)for the diesel one, you get the idea.

Using that l/100km way of measuring, a vehicle is consuming infinite amounts of fuel per 100km when stopped, because the vehicle is stationary while sipping fuel. Hence, the display maxes out instant fuel consumption.

When translating to US mpg, the same display ends up being a bit illogical. But thats because the display got translated to a different way of measuring. The Brits and US just don't use the proper units.

markl53
01-11-2011, 06:47 PM
The reason the newer digital display shows infinity during a stop is simply because of a conversion factor and the way fuel consumption is measured.

In most countries (EU, Canada), fuel consumption is measured in l/100km (amount of fuel consumed in a given distance. See here (http://www.treffbilder.de/93747769img_1143wuw-jpg.html)for the diesel one, you get the idea.

Using that l/100km way of measuring, a vehicle is consuming infinite amounts of fuel per 100km when stopped, because the vehicle is stationary while sipping fuel. Hence, the display maxes out instant fuel consumption.

When translating to US mpg, the same display ends up being a bit illogical. But thats because the display got translated to a different way of measuring. The Brits and US just don't use the proper units.

Regardless, they could make the display work any way they want, including when the vehicle is stopped.

AzNMpower32
01-11-2011, 07:24 PM
Regardless, they could make the display work any way they want, including when the vehicle is stopped.
They're not bothered. They design major components to work best in German logic. Just like how the temperature/time/board computer readout digits are perfectly lined up using metric, and how the oil temp markings make more sense in C.

Honestly the newer instant consumption meter doesn't work great with US mpg. The vehicle consumes no fuel when coasting (torque converter locked), consumes negative fuel under regenerative braking, and consumes infinite fuel when stopped.

Rafa
01-11-2011, 07:24 PM
Regardless, they could make the display work any way they want, including when the vehicle is stopped.

I agree. It shouldn't be difficult at all to produce a display that returns 0 mpg when the vehicle is doing 0 mpg.

Why not make the mpg display show 0 mpg when the vehicle is in fact doing 0 mpg? There must be an explanation... Does anyone have any ideas?