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MPG gauge
The MPG gauge on my 04' 530 swings back and forth on my daily drive. Is that normal?? The gauge does not stay constant, but will swing wildly from a reading of 12mpg to 50mpg and vice versa.  My OBC gives me a reading of 19 MPG. I don't pay attention to that MPG gauge anymore, cuz I'm not sure if it's working correctly. Does anyone have the same problem? Do I need to take it to the dealer?  thanks. | | Reply » MPG gauge |
Relax folks. It is a BMW tradition to have this instrument. It simply measures real time intake manifold vacuum, nothing more, nothing less. If it fluctuates during idle, I'll bet the A/C is on and the compressor is cycling on/off.
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Quote: | Relax folks. It is a BMW tradition to have this instrument. It simply measures real time intake manifold vacuum, nothing more, nothing less. If it fluctuates during idle, I'll bet the A/C is on and the compressor is cycling on/off. | No, no it doesn't. Don't relax, folks  . This misinformation crops up time and again. This is not a vacuum gauge, it uses injector info and road speed to work out the instantaneous consumption, and then buffers the output to prevent the dial from moving too fast to be of use. What most people don't realise is just how wildly instantaneous comsumption varies, and why would they? They've never seen a gauge like this before.
For those who think this is a vacuum gauge, I'd like to ask: how does BMW manage to get a dial like this to work on the diesels? Or, for that matter, the Valvetronic system, which is now in widespread use?
Perhaps they should remove them from US-market cars and cars for other countries where fuel is less than xx per gallon/litre etc. I pay nearly $7/gallon, and that "silly little gauge" is quite good at reminding me when I am unnecessarily burning money that I should be putting towards my childrens' education.
Sorry to be so po-faced about it .
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That does make sense when i think about it. So, my MPG gauge is not broken when it jumps wildly...my foot is just heavy on the accelerator  I just can't help it sometimes. This is my first BMW/performance car. Even if i drive just three blocks away, i get this urge to pucnh it. Hello my name is JOE and I am a speed junkie 
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I actually think the needle does a pretty good job and is reasonable... IF you think about the following: only while driving at some steady speed (when stopped speed=0) can you estimate MPG. At 0 speed, mathematically, you would either have 0 MPG or inifinite MPG. So to avoid a "divide by 0" situation the needle swings to the off or left position) yet at some point as you accelerate it must go toward some more realistic value.
Its a difficult problem to make such a gauge and I think what BMW did is useful to me. For whats its worth, my $.02 -steve-
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MPG gauge