[cowmoo32]

OK...when I approach a stop light or stop sign, I usually shift into second, slow down, and then shift to neutral and use the brakes. But as I'm slowing down, and when I come to a stop, the MPG needle creeps up and up and then finally falls back to 50. Does this happen to anyone else? Why does it do this?

Here's a video:
http://kandeecup.tripod.com/MPG.wmv

 

[Dalton]

happens to me too, i dont think anything is "wrong"

i'll take a look at the video tho...

edit: yeah, same thing happens to me...its "normal"

 

[B8888KC]

Looks normal. Happens all the time to my car.

 

[cowmoo32]

I was thinking it was the engine doing something, but then again, wouldn't the RPMs change?

 

[Krzysztof]

change your 325Ci to M3 (without f__g MPG needle) and the problem is out!

 

[B8888KC]

It's been happening to my car ever since the first day I picked it up. It's very normal.

 

[Tenchi]

i can't get video

 

[Dalton]

i can't get video

you have to right click and save as or else it wont work

 

[323iT]

yea happens to me too. I assumed its normal:dunno:

 

[cowmoo32]

Ok, so nothing is wrong, we've figured that out. But does anyone know WHY its doing it?

 

[323iT]

I would guess like the engine is like revving or something... something to do with the software..:hmm:
actually now that i thought about it... my car didn't do that at first...
i think after 10k miles it started do it...:hmm:

 

[cowmoo32]

I would guess like the engine is like revving or something... something to do with the software..:hmm:

That's what I thought, but the RPMs dont change :dunno:

 

[wolf328ci]

My friend and I have

hypothesized that the mpg gauge is based on manifold vaccuum pressure, since it moves in much the same way as a vaccuum gauge or a boost gauge with a vaccuum section. Those gauges always flip around when taking the engine through these types of motions. It would make sense in terms of reading estimated mpg too, since effectively a vaccuum gauge can tell you how wide open your throttle butterflies are. Just a thought.

 

[abomb]

Because instant MPG is calculated using fuel consumption rate and vehicle speed. When you are in neutal the engine is idling so it still consumes fuel. As you slow down fuel consumption is constant but vehicle speed becomes reduced, so MPG approaches zero. Finally, when vehicle speed becomes slow enough, the gauge returns to it's "off" point which is to the far left. It would be a lot more logical if the MPG gauge went to zero on the right, but since the gauge returns to the far left when MPG is zero, it moves right at first then left when you're almost stopped.

 

[cowmoo32]

Because instant MPG is calculated using fuel consumption rate and vehicle speed. When you are in neutal the engine is idling so it still consumes fuel. As you slow down fuel consumption is constant but vehicle speed becomes reduced, so MPG approaches zero. Finally, when vehicle speed becomes slow enough, the gauge returns to it's "off" point which is to the far left. It would be a lot more logical if the MPG gauge went to zero on the right, but since the gauge returns to the far left when MPG is zero, it moves right at first then left when you're almost stopped.

THanks

 

[Cesium 911]

it always happens to me and is completely normal...i contacted BMWNA and they told me all it is doing is recalibrating its self :thumbup: actually if it isn't doing it you should have it checked