Trip Computer / Fuel Consumption Accuracy

[Chris_08_M3]

Is it just me or is the fuel consumption gauge/computer inaccurate? I typically get 350 KMs per tank which I when I fill up requires 57 liters of gas. So by my calculation the reading should be 16.3L/100KMs but my screen shows 14.1L/100KMs. Am I missing something here?

Chris

[kaede]

Originally Posted by Chris_08_M3

Is it just me or is the fuel consumption gauge/computer inaccurate? I typically get 350 KMs per tank which I when I fill up requires 57 liters of gas. So by my calculation the reading should be 16.3L/100KMs but my screen shows 14.1L/100KMs. Am I missing something here?

Chris

Wow... you drive the M3 hard. Personally, I drive mine almost 90%+ in the City and I do occasionally step on it. Fuelly (fuel consumption tracking app i use) have always calculated and tracked approximately 13.5L/100km, but trip computer says something like 12.4L/100km. Seems like Trip computer will alway return a better than real life reading that's why i track my own fuel consumption. Cheers!

[ResoKP]

Originally Posted by Chris_08_M3

Is it just me or is the fuel consumption gauge/computer inaccurate? I typically get 350 KMs per tank which I when I fill up requires 57 liters of gas. So by my calculation the reading should be 16.3L/100KMs but my screen shows 14.1L/100KMs. Am I missing something here?

Chris

My screen currently shows 14.1L/100KM as well...

Coincidence?

[DSilk]

Originally Posted by Chris_08_M3

Is it just me or is the fuel consumption gauge/computer inaccurate? I typically get 350 KMs per tank which I when I fill up requires 57 liters of gas. So by my calculation the reading should be 16.3L/100KMs but my screen shows 14.1L/100KMs. Am I missing something here?

Chris

Clearly the calculation is off, but you are getting terrible mileage. 350 kms is roughly 219 miles, and that's all you are getting in out of 57 litres (roughly 15 gallons)? That's about 14.6 miles per gallon. I average 18.5 mpg, and I drive relatively fast, and in a hot climate that requires air conditioning almost 12 months a year....

[Helmsman]

Originally Posted by Chris_08_M3

Is it just me or is the fuel consumption gauge/computer inaccurate? I typically get 350 KMs per tank which I when I fill up requires 57 liters of gas. So by my calculation the reading should be 16.3L/100KMs but my screen shows 14.1L/100KMs. Am I missing something here?

Chris

Yes, the computer sucks. Better on long distance but bmw have clearly skewed this on the M3 as worked fine on my previous models...

[Helmsman]

Originally Posted by kaede

Wow... you drive the M3 hard. Personally, I drive mine almost 90%+ in the City and I do occasionally step on it. Fuelly (fuel consumption tracking app i use) have always calculated and tracked approximately 13.5L/100km, but trip computer says something like 12.4L/100km. Seems like Trip computer will alway return a better than real life reading that's why i track my own fuel consumption. Cheers!

13.5l/100km is really good, how do you manage that mate, never touch the pedal..?? Mix driving if I really try I may come down to around 1.5l. City driving that simply is not possible...

[ash4390]

Just to echo what people are saying, my display vs calculated is always off as well.

Says I average 14-14.3L/100km usually, but my calculations have me around 15.5-16L/100km.

I don't drive my car hard at ALL in the city, it just gets horrible mileage haha. Even using start-stop, etc.

[Chris_08_M3]

Originally Posted by kaede

Wow... you drive the M3 hard. Personally, I drive mine almost 90%+ in the City and I do occasionally step on it. Fuelly (fuel consumption tracking app i use) have always calculated and tracked approximately 13.5L/100km, but trip computer says something like 12.4L/100km. Seems like Trip computer will alway return a better than real life reading that's why i track my own fuel consumption. Cheers!

I think I maybe step on it once or twice a day...nothing too crazy

[drummer20]

what is all this L/km business??? my head exploded haha maybe if it had been km/L at least I might have survived

fyi my computer reads 14.1 M/G but I never cruise with RPMs below 2K so I burn a little extra gas staying in a lower gear

[Chris_08_M3]

Looks like we are all over the place...most of us get pretty bad mileage...a couple have gotten really good though.

Why don't we just post how much miles or KM we get on a tank vs the per mile/KM reading.

BTW even if I drive conservatively I cannot get more than 370 km on a tank (90% city). How are you guys doing it?

[kb9uwu]

Originally Posted by Chris_08_M3

Why don't we just post how much miles or KM we get on a tank vs the per mile/KM reading.

I fill up at 1/4 usually but sometimes at 1/6-1/8 tank, so I'm not sure that would be the best way to compute mileage.

I consistently get 16mpg city and 20mpg hwy, +/-1mpg, calculated at pump.

[Chris_08_M3]

Originally Posted by ResoKP

My screen currently shows 14.1L/100KM as well...

Coincidence?

Maybe its the Toronto air!

[ivad32]

In my three years of ownership, I have tracked 37 fill-ups with both OBC data and the manual method, miles/gallons.

N=37
OBC average MPG = 18.37
manual MPG = 16.87
% error = 8.9%

Here is a graph of OBC verse manual MPG sorted from lowest MPG to highest. For the most part, the error is consistent except at the upper and lower extremes:

[drummer20]

oh awesome that means I am near high 12s in MPG, always wanted a car that could do 12s haha

I have a fairly heavy foot and 90% stop and go stoplight traffic so I believe it

[CHE///MIST3]

Can anyone confirm that if you have the newer engine software "240E" that better mileage is attained than when the these cars first came out? Mine has 2009 software as I recently found out! I'll be getting the update soon...

By calculating at the pump I get 16.5 MPG mixed city/hwy driving...practically every time.

GM

[OldenburgerM3]

17mpg average here in five years. That's gas station math, not onboard computer. 192 fill-ups. I've previously calculated about 9-12% error on the computer. Unlike Audi or older BMWs I've learned that it's not adjustable through a secret menu.
That's 13.84 l/100km in old math.

[BanjoPaterson]

Originally Posted by Helmsman

Yes, the computer sucks. Better on long distance but bmw have clearly skewed this on the M3 as worked fine on my previous models...

Yep - my trip computer gives me something like 10-12 ltrs per 100 kms. [edited this after checking]

Hopelessly optimistic... if only...

[kaede]

Originally Posted by Helmsman

13.5l/100km is really good, how do you manage that mate, never touch the pedal..?? Mix driving if I really try I may come down to around 1.5l. City driving that simply is not possible...

I have started tracking my mileage with fuelly around 30k km's ago, and my average so far is 13.1L/100km (almost 18mpg). I do almost 90%+ city driving as there is basically little to no highways here in Vancouver area where i commute and go about.

I do touch the pedal… open up the throttle once in a while on the bridges and open roads. Also, during the hotter days (past 2 months or so?) i have consistently had my A/C on…

Some of the things that have decreased my fuel consumption for sure is when i switched the tune to the newest 240E, helped me dropped 0.5-1L/100km consistently while tracking. Also the tune made the car rev free'er and just seems to give the engine tiny bit more umph. I use my cruise control whenever i can when I'm "stuck" in regular traffic. Lastly, here in Canada we have access to fuel that have NO ethanol added. For NA engines, 0% ethanol works better as the fuel is more energy dense = computer sprays less to compensate.

Cheers!

[kaede]

Originally Posted by GMCHEM83

Can anyone confirm that if you have the newer engine software "240E" that better mileage is attained than when the these cars first came out? Mine has 2009 software as I recently found out! I'll be getting the update soon...

By calculating at the pump I get 16.5 MPG mixed city/hwy driving...practically every time.

GM

As mentioned above from my other reply, when i updated the software it definitely gave me better fuel economy (however, it is NOT at all a HUGE improvement). Also, YMMV because the tune seem to make the engine a little bit more peppy and you might actually end up revving it and driving it even harder

[kaede]

Originally Posted by Chris_08_M3

Looks like we are all over the place...most of us get pretty bad mileage...a couple have gotten really good though.

Why don't we just post how much miles or KM we get on a tank vs the per mile/KM reading.

BTW even if I drive conservatively I cannot get more than 370 km on a tank (90% city). How are you guys doing it?

I can consistently hit 400km on a tank before the it drops before the "fuel up" warning stays on.

[kaede]

Originally Posted by Chris_08_M3

Maybe its the Toronto air!

Possibly. Toronto definitely have more humid air than Vancouver. To top it off, temperature is also consistently hotter which makes oxygen level lower and combustion suffer. To compensate for that, it's only natural that the engine possibly dumps in more fuel? (I COULD BE TOTALLY WRONG THOUGH since i am no engine computer and management expert, please don't flame me >_<)

Base on that, cooler more oxygen dense and drier air should produce a better combustion which requires less fuel for the same/similar performance.

Also, i mentioned previously about fuel type too. Ethanol blended fuel is less energy dense and thus requires more fuel, try running gas without ethanol and you should notice an increase in fuel economy. Here on the West Coast we have Shell V-Power 91 Octane and Chevron 94 Octane that is ethanol free. I am guessing in Toronto it should be the same?

Cheers!

[Chris_08_M3]

Originally Posted by kaede

I can consistently hit 400km on a tank before the it drops before the "fuel up" warning stays on.

That is amazing mileage...I get to 300 km when the warning comes on (with 100km range left) and then I push it 50 km more. I'm also using Shell V Power 91 octane. I'm pretty sure I'm on the latest 240E software too. Even if I drive very conservatively I cannot hit 400 km on a tank. Maybe it is the humidity in Toronto vs Vancouver