530i E39 board computer figures

[RiccardoG]

Hi,

On my E39 the board computer seems always to display high fuel consumption rates. After a 260 mi trip (there and back) at leisurely motorway speeds it was showing 18.8 mpg... This while the instant consumption gauge was regularly showing anywhere between 25 and 40 mpg.

I do very few miles and quite a few are in central London, so I can understand why it would show the usual 17 mpg when I am in the city, but wouldn't the figure have improved after such a long trip?

Its all academic as I don't really care given that I have driven only 2500 miles in one year, but was just curious as to why the computer is so slow to react.

Thanks

[Origin Unknown]

My E39 530i achieves around 28/29 MPG on that sort of motorway trip so you are well down. I can't even think of what may cause such a reduction in MPG to be honest. Do those figures fit when you look at how much petrol you used over that journey?

[RiccardoG]

I am thinking that the computer is off, but what I'd like to understand is if it can be reset in some way.

I don't drive enough to check the consumption, I think I used half tank for about 150 miles, therefore about 300 miles per tank on motorway. Does that sound about right for you?

[miniman]

My 523 would do about 300 miles on a tank, mix of B-roads and motorways mostly.

[trickywoo]

Im guessing your 18.8 is a long term average so it would take a fair bit of much more economical motoring to see it go up.

Don't you have two seperate consumption calculations? I do on my 528. I leave one as the long term average and reset the other after a fill up or a 'special' journey.

Edited by trickywoo on Tuesday 30th November 15:07

[Origin Unknown]

Trickywoo might be on the money, did you rest the counter before you set off? As said, there are 2 -> I keep one as a forever average and the other I reset if I'm actually interested in a journeys MPG

ETA - 300 miles out of a tank sounds about right to me

Edited by Origin Unknown on Tuesday 30th November 17:03

[BliarOut]

trickywoo said:

Im guessing your 18.8 is a long term average so it would take a fair bit of much more economical motoring to see it go up.

Don't you have two seperate consumption calculations? I do on my 528. I leave one as the long term average and reset the other after a fill up or a 'special' journey.

Edited by trickywoo on Tuesday 30th November 15:07

This.... Exactly this

[RiccardoG]

Thanks guys, sounds like a feasible solution. Only thing is that I have the basic computer and it doesn't seem to me like there are two average mpg readouts, will check next time I am in the car as its something I haven't paid too much attention to.

Any guesses on how I could toggle between the two readouts, assuming I have the two? I only have one button on the stalk and thats it.

[BliarOut]

Do you have a button on the centre console that says BC?

[RiccardoG]

BliarOut said:

Do you have a button on the centre console that says BC?

I don't think so, not on the centre console, there I have PDC and DSC buttons only. I access the computer thingy through the LH stalk by pushing it in (towards the steering column).

Car is a basic trim SE.

[miniman]

I might be thinking of a completely different car (possibly my wife's Fabia which certainly has it) but - doesn't the E39 detect which ignition key is being used and set the OBC accordingly?

[Valetco]

How many service lights gave you got? Resetting mine increased the claimed mpg via the computer by 15%! Tank to tank mpg was the same make of that what you will

[matt21]

easy. brim tank. reset odometer (trip) and MPG counter. run to (close to) empty. fill.

Divide number of litres by 4.54. Then divide that figure into the miles elapsed on the odometer. Real MPG.

Then look at MPG trip computer. If significantly different note % over or under.

Hold down check control button (if you have one) until test mode comes up. Cycle to test one. Enter. Add up five digits displayed. This is the number that unlocks test mode.

Scroll to test mode 19. Enter five digit number when it says lock to unlock.

Take %age above and divide or multiple depending the figure of 1000 (over read go above 1000 under read go under). This then recalibrates the trip based on the new factor. You have a exact MPG.

Since running on gas mine was over reading on the computer. Cue entering a figure of 1231 and all is good.

Yes I'm a geek