Weird Fuel Eco calculation with idling

[mypatpat]

I was playing with the trip computer one day and noticed that the average fuel comsumption goes up when idling. It wasn\'t obvious as first since the computer collects thousands of data samples a day, if not more, a few outliers shouldn\'t have a dramatic affect on the average comsumption. It caught my attention when it jumped from 10.1 to 10.2 after around 45 min of idling, considering that I have not reset my average fuel consumption for almost a month, the 0.1 difference rang a big bell.

Immediately I resetted the average and wait for the first data sample, not to my surprise it showed 999.9L/100Km. Now, I know that idling uses up gas, afterall something have got to keep the engine running. But this looks more like a defect than even an educated guess, I really doubt that it\'s a calculated value. Any input on this?

[majic]

Originally posted by mypatpat
It caught my attention when it jumped from 10.1 to 10.2 after around 45 min of idling


first of all.. WTF are you doing idling for 45min???????? :sarc

second of all.. average is what it is example:

avg(100+100+100+1+1+1)=55.5

take 100 to be your idling L/100 and 1 to be your highway L/100km.. well if you START idling.. obviously your avg is going to be 100 and remain ther until you are moving.. then it\'ll drop.. and over a longer time frame it\'ll come down to your actual average (in theory)

[mypatpat]

Originally posted by majic



Originally posted by mypatpat
It caught my attention when it jumped from 10.1 to 10.2 after around 45 min of idling


first of all.. WTF are you doing idling for 45min???????? :sarc

second of all.. average is what it is example:

avg(100+100+100+1+1+1)=55.5

take 100 to be your idling L/100 and 1 to be your highway L/100km.. well if you START idling.. obviously your avg is going to be 100 and remain ther until you are moving.. then it\'ll drop.. and over a longer time frame it\'ll come down to your actual average (in theory)

I know what an average is, and I\'m not saying the average calculation is wrong. In fact, it is so accurate that it doesn\'t staticially remove the outliers and made the calculated value wrong!

Quote from my first post:


Immediately I resetted the average and wait for the first data sample, not to my surprise it showed 999.9L/100Km.

I\'m simply saying that when the car the idling, the trip computer enters 999.9L/100Km as a data point at every interval (10 sec or whatever). The end result after your above example becomes avg(999.9+999.9+999.9+1+1+1)= 500.45.

Never thought I\'ll be saying this to the almighty majic but...read my post carefully :p

[majic]

lol.. ok.. so i reread your post and i\'m confused :p

from what i read:
1) when idling for 45min (w00000t) average L/100km went up from 10.1 to 10.2 - MAKES sense.. u idled for a DAMNED long time!!! i\'m surprised it didn\'t shoot up to 12 or so..
2) when you are NOT moving mpg = 0 or L/100km becomes infinity.. it would be nice if the stere could show a tilted \"8\" but the most it can do is 999.9 (i assume sincei have 05 model) so since you\'re not moving it\'s showing you its internal infinity

where did i go wrong? :D i just woke up.. leave me alone :p you never mentioned your 999.9L/100km \'avarage\' improving once you started moving your car..

as for my 100s and 1s.. they were arbitrary numbers.. and i don\'t know what the standing still consumption is but it\'ll all even out (maybe it\'s weighted average, i dunno ask mazda :)..

[Jeff-TheBiz]

Originally posted by mypatpat


Immediately I resetted the average and wait for the first data sample, not to my surprise it showed 999.9L/100Km.

I\'m simply saying that when the car the idling, the trip computer enters 999.9L/100Km as a data point at every interval (10 sec or whatever). The end result after your above example becomes avg(999.9+999.9+999.9+1+1+1)= 500.45.

Never thought I\'ll be saying this to the almighty majic but...read my post carefully :p

(999.9+999.9+999.9+1+1+1)= 500.45 I tried this calculation on my calculator and it worked out differently.. :D

I think it goes to a default when you divide by 0

litres used / km travelled = average consumption

1 L / 0 km = 999.99

just my $.02

[mypatpat]

Average Jeff average! Divide the total by 6...

I know it can\'t display/interpert infinity, thus it displays 999.9. I\'m just thinking that 999.9 or inifinity for that matter doesn\'t necessarily represent the fuel consumption when idling.

[Optimzer]

infinity sure does represent the fuel consumption rate when idling.

think of it, fuel consumption rate represents volume of gas used per distance travelled. like Jeff\'s example (1L / 0km), if you travel no distance, then your fuel consumption rate is infinity (you\'re using a lot of fuel, and moving no where)..

at least i think that\'s what you\'re question is saying...;)

[Junior]

milage calculator (http://kgm.tiwing.com/mileage_cost_calc.htm)

[john_ertw]

It may use a different calculation:

the total fuel used since the last reset divided by the total distance travelled since the last reset.

While idleing you may use whatever amount of fuel, but travel 0km. so this will increase the L/100km.

[Junior]

a car could idle on fumes for 7 days. what\'s the point? this is a bit \'outlandish\'

:sarc