View Full Version : OBC Fuel Consumption Accuracy

Fern3

12-10-2010, 12:38 PM

On the highway today driving like a 60 year old I hit an avg consumption of 5.7 l/100km. kept that figure for the whole trip down to oshawa from mississauga (hit 5.6 at random times as well) I was just wondering does the obc calculate that number based on real time distance values vs. calculated amount of fuel remaining in the tank or is this all from a preloaded chart in which the obc just throws out a number based on throttle position/engine load?

InfiniteDice

12-10-2010, 02:31 PM

It knows how much fuel is passing through the injectors (flow of injector, duration, rpm, etc.) If you mess with stuff and some part of the injection system is not stock, your reading could be off. In that case record and keep track of distance driven manually, then do the math.

If it knows how much gas you're using (plotted over time) it can then make an assumption about how far you can drive based on how much fuel is left in the tank.

SickFinga

12-10-2010, 08:03 PM

InfiniteDice, is right. It appears since you swapped your engine from m52b25 to m52b28 your injectors are different now. If I remember correctly 323i uses M50 injectors. So you went from 17.5lbs/h injectors to 21.5lbs/h.

In the OBC there is a menu that allows you to change the formula by which the fuel consumption is calculated.

Since your injectors are now 23% larger, adjust the formula number by 23%. That's what I would do.

doogee

12-10-2010, 08:20 PM

InfiniteDice, is right. It appears since you swapped your engine from m52b25 to m52b28 your injectors are different now. If I remember correctly 323i uses M50 injectors. So you went from 17.5lbs/h injectors to 21.5lbs/h.

In the OBC there is a menu that allows you to change the formula by which the fuel consumption is calculated.

Since your injectors are now 23% larger, adjust the formula number by 23%. That's what I would do.

He's exactly right.

You need to change the values for it to be accurate.

Fern3

12-11-2010, 11:02 AM

Thanks for all the helpful info guys! I will manually calculate my consumption for this tank and adjust the correction factor from there. Correction factor is obc mpg reading/actual mpg. Correct?

pawcio

12-11-2010, 11:18 AM

Thanks for all the helpful info guys! I will manually calculate my consumption for this tank and adjust the correction factor from there. Correction factor is obc mpg reading/actual mpg. Correct?

if you mean the correction factor to calculate your actual mpg after you look at the obc readout then: correction factor= actual mpg/obc mpg....in this way once you have a correction factor: Actual mpg = obc mpg x correction factor

tg07lq

12-11-2010, 12:48 PM

ive actually found all my systems to be pretty accurate, overall im incredibly impressed actually. both the absolute gas gauge, the obc volume , even the fuel consumption per hour have helped aleviate some stressful situations (like having a friend return my car to me at the cottage with next to no gas, and no station near by)

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