Fuel Consuption Guage Under Tach - BMW Forum - BimmerWerkz.com
3-Series (E21, E30) Chat relating to the BMW 3-Series from 1975-1983 and 1984-1991 line. Specific models: BMW 315, BMW 316, BMW 318, BMW 318i, BMW 320/4, BMW 320i, BMW 320/6, BMW 323i, BMW 320i. E30 Family models include: BMW 325e, BMW 325i, BMW 325is, BMW 325ix.

 
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#1 (permalink) Old 03-24-2005, 11:04 PM
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I have an 1991 318is and the fuel consumption that is under my tach didn't work so I took the cluster out and found that the needle was "hung up" on that little pin that in bottoms out on. SO I took it off and now my brake pedal doesn't return on its own. Obviously I have a vacuum leak somewhere or I assume I do?????? Anyone know what's going on?? Any help would be greatly appreciated
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#2 (permalink) Old 03-24-2005, 11:45 PM
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Those two things are completly unrelated. The dash is all eletronic and has no vacuum going to it. Sounds like the brake master cylinder went out.
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#3 (permalink) Old 03-27-2005, 12:36 AM
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the fuel consumption gauge is actually derived by vacuum, or a lack of, in the manifold... high vacuum tells it that you are getting great gas milage and low means you've got your foot down on the gas pedal! just thought id add my two cents...

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#4 (permalink) Old 03-27-2005, 03:49 PM
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Originally posted by ae.cowboy@Mar 27 2005, 12:36 AM
the fuel consumption gauge is actually derived by vacuum, or a lack of, in the manifold... high vacuum tells it that you are getting great gas milage and low means you've got your foot down on the gas pedal! just thought id add my two cents...
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yeah i agree, its what i thought!

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#5 (permalink) Old 03-28-2005, 10:59 PM
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Actually the DME looks at throttle positon and injector pulsewidth and then gives you your instant MPG. It is true that some cars use engine vac. to give instant MPG but that is not how BMW does it.
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#6 (permalink) Old 03-30-2005, 05:25 PM
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Hmmm...

1) The instrument panel is electronic, save for the speedo needle. As far as I know, these panels tend to malfunction after some tears of use. My dad's 325e has the fuel consumption gauge and which sometimes acts erratically along with the temperature gauge (located just above the economy gauge). I'm aware that the problem can be solved by removing the panel and replacing some rechargeable batteries, which also cures the service interval indicator and oilservice problem (they refuse to stay off even after a reset has been made, and the batteries are there to backup the state after the reset- if they are bad the computer never resets properly) . The funny thing is that almost always the service lights problem appears first and then the other gauge problems.
I believe the complete solution was in BMWe30.net, just in case (post here if you want me to put it here, I think I have it in one of my older backups)

2.- I don't know if the economy meter is connected to some vacuum line that senses the vacuum in the throttle body, as it is on some older or simpler cars. I think the economy meter is connected to a signal from the DME, since the DME always know how much fuel is injecting (via the airflow sensor). I don't think the germans would put a vacuum line to the throttle body if they already had a means to electronically measure it. But on second thought the E30 was designed in the early 80's and many models were carburetted (the 315, 316 and 318), so maybe the vaccum system is there.

3.- If you have a vacuum leak in the intake tract that would affect the performance of the brakes and also the readings of the airflow sensor, which in turn would also affect the gauge reading. You should also be experiencing severe problems with drivabitlity and idle due to the varying vacuum (altough I wouldn't drive a car with a brake pedal going to the floor). So yes, the two problems may be related, though I don't see how removing a little pin would have an effect in your brake system (especially if you assembled it all back together) Maybe you messed the electronics?

Hope this helps
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