Actual fuel consumption doesn't match onboard computer

[m9679]

Sorry if this has been done before. I can't find a previous thread.

So, I brim the car with gas, reset the odo and onboard computer fuel consumption calc, then drive until the fuel warning comes on, then repeat. The onboard computer shows say 15.5l/100km (apparently about 15.1 MPG US). However when I refill I see that I have consumed 50 litres of fuel and travelled 290km. That is an actual 17.2l/100km (13.7 MPG US). I've done this on at least two tanks now, and the previous error was even worse. I've checked the tank was being properly brimmed each time, so the error there would be minimal.

Ignoring the fact that this isn't great mielage (almost all urban and not complaining about the mileage itself) this is the biggest computer error I have seen in a modern car. Anyone else seeing this? BMW doing this on purpose to fiddle the numbers that 95% of drivers wouldn't verify?

This is an E92 HP from 2009 running on premium 98 octane. Apparently not the very latest software, but one click off.

[alpina527]

What size tyres are you using?

My brim to brim and obc figures are almost identical. I use UK MPG

[m9679]

Everything is OEM. Not sure the exact tyre sizes but they are the standard Michelin Pilot Sport 2s on 19" wheels.

[m9679]

Forgot to say, this is a DCT car.

[1MORELAP]

I never checked. I guess it is time to do so.

[BobsM3Coupe]

No matter the mfg., those onboard mpg results are almost always optimistic by 1-2 mpg.
The most acurate way is to fill the tank, reset trip odometer to zero or write down the miles, including the tenths, divide the miles driven by the gallons and tenths it takes to fill the tank. Simple and accurate.

[smmmurf]

mine says 15 and i get 13-14, so you are right

[aus]

This is pretty typical for BMW computers. Our 335 is the same as did the X5 we had.

[dpiette]

Here is four years worth of data on the 550i I sold in December.

The computer (which I never reset) told me that I was getting 21 MPG. That is about 10% off.

But given the fact that most speedometers are (apparently) about 10% off, this may be consistent with the design of the car.

I don't have enough data on my 2011 E90 yet, but will post it when I do.

[besiktas]

I have the same problem, on highway, the car says i get 24 mpg but i actually get 21 ish

[Richbot]

You can adjust this via the hidden OBC functions. There's a DIY on the e90post.com forums somewhere. Mine's dead on now, was about 10% optimistic from the factory before I adjusted it. For whatever reason, my 335xi has always been dead on from the factory.

[drjoe66]

I just measured this over four tanks. I got 16.9 per computer and 15.5 calculated.

[V1.47fan]

Originally Posted by m9679

Sorry if this has been done before. I can't find a previous thread.

So, I brim the car with gas, reset the odo and onboard computer fuel consumption calc, then drive until the fuel warning comes on, then repeat. The onboard computer shows say 15.5l/100km (apparently about 15.1 MPG US). However when I refill I see that I have consumed 50 litres of fuel and travelled 290km. That is an actual 17.2l/100km (13.7 MPG US). I've done this on at least two tanks now, and the previous error was even worse. I've checked the tank was being properly brimmed each time, so the error there would be minimal.

Ignoring the fact that this isn't great mielage (almost all urban and not complaining about the mileage itself) this is the biggest computer error I have seen in a modern car. Anyone else seeing this? BMW doing this on purpose to fiddle the numbers that 95% of drivers wouldn't verify?

This is an E92 HP from 2009 running on premium 98 octane. Apparently not the very latest software, but one click off.

We had a Volvo truck with a fuel consumption meter that was about 10% off,almost always when a fuel meter is off, it shows better fuel consumption than actual,i've never seen it the other way around.
It's like phone companies when they make billing errors it's usually to their advantage.

[OldenburgerM3]

Mine's off as well, still trying to determine the %-error. Uncle's Audi has an adjustment feature, that has been adjusted at the Audi dealer. Apparently the error was 8% optimistic, now the factory setting has been changed from 100 to 108 and waiting on the first tank.
Wonder if the BMW-folks can do an adjustment when I show up next week.

[OldenburgerM3]

Went to the dealer, they didn't know about any option to change the MPG display. Richbot, any idea where you saw a DIY?

[MSPORTWORLD]

I've calculated a few tanks of gas and my computer has averaged 19.1mpg an my calculated is 18.2 mpg.

Not too shabby...

[dreamspeed]

I know this is an old thread but i didn't see a point in starting a new one.

I wanted to add that i've had similar results as the posts above. The onboard computer is showing about 1.5mpg higher than what i am actually getting

[roddyc]

http://www.e90post.com/forums/showthread.php?t=472204

Gonna try changing the correction factor this weekend since my OBC consistently reads about 10% higher than actual calculated MPG.

So assuming my correction factor is 1000, I should change it to 1100 right?

[BMWJ]

Actually the BMW odometer is optimistic... you haven't driven as many miles as it claims. Notice how the speedo is optimistic as well.

Not that it should matter since you're using the same calculation for miles either way.

[davesaddiction]

Similar results here. Thanks for the hidden menu link.

[mdosu]

Originally Posted by BMWJ

Actually the BMW odometer is optimistic... you haven't driven as many miles as it claims. Notice how the speedo is optimistic as well.

Not that it should matter since you're using the same calculation for miles either way.

whaaa? Odometer is wrong?

[Chriskm3]

I fill my tank and get 240km of spirited driving.
Great car.!!! Every time I start it it feels like the first time.