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Go Back   Bimmerfest - BMW Forums > BMW Model Discussions > 5 Series > E39 (1997 - 2003)

E39 (1997 - 2003)
The BMW 5-Series (E39 chassis) was introduced in the United States as a 1997 model year car and lasted until the 2004 when the E60 chassis was released. The United States saw several variations including the 525i, 528i, 530i and 540i. -- View the E39 Wiki

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  #1  
Old 09-29-2012, 07:19 PM
TheHockeytowner TheHockeytowner is offline
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Location: Ann Arbor, MI
 
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Mein Auto: 2003 525i
MPG gauge creeps upon braking

I apologize if this has been addressed already, but I didn't find anything useful through searching.

The car is a 2003 525i. Today I replaced all of the SAS vacuum hoses, as well as the vacuum hose from the F connector on the intake boot. It's nice not having the CE light on all the time, but now my MPG gauge is acting funny.

The needle reads normally while driving, but now whenever I start to brake before a stop sign/traffic light, it slowly goes down to around 15 and then comes back up when I come to a complete stop.

Is this normal behavior for the MPG gauge? I think it has something to do with the hose off of the intake. Where does that pipe end up?
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  #2  
Old 09-29-2012, 07:32 PM
gotrice415 gotrice415 is offline
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Mein Auto: M3, 335Ci, X5d, 750i
You'll need to recheck your vacuum lines. You may have mixed up the lines. The MPG gauge is activated by engine vacuum, yes like old Dodges. You can trace it by following the line that comes from the firewall.

Good Luck.
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  #3  
Old 09-29-2012, 07:46 PM
TheHockeytowner TheHockeytowner is offline
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Location: Ann Arbor, MI
 
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Mein Auto: 2003 525i
Well, the SAS system functions correctly, and I double-checked the orientation of the check valve and the connections on the small electronic valve.

I wonder if one or both of the larger vacuum hoses on the sucking jet pump got dislodged or something. Would that cause a CE?
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  #4  
Old 09-29-2012, 08:02 PM
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doru doru is offline
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Mein Auto: 2003 530iA
I believe your MPG gauge functions correct.
If it goes to the right when stepping on the brakes, and the speed is substantially reduced, the mpg gauge goes almost all the way to the right, and once stopped, it goes to "0" (all the way to the left)
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  #5  
Old 09-29-2012, 08:04 PM
TheHockeytowner TheHockeytowner is offline
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Gotrice and Doru, thank you for the replies.

Interesting! All this time it never did that.
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  #6  
Old 09-29-2012, 10:53 PM
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bluebee bluebee is offline
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Mein Auto: 02 BMW 525i M54 automatic
We have mpg gauges on our clusters?

Seriously, that silly gauge seems to me to be a JC Whitney add-on by BMW marketing to sell cars in the showroom.

Do people 'really' look at that thing fluctuating while they're driving?

I'd rather use the cell phone!

< / end of commentary >
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  #7  
Old 09-20-2013, 07:39 AM
chevl71 chevl71 is offline
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My car has just started doing this too (MPG creeping down when coasting and braking). It didn't do that before. 2003 525i, manual trans.

It started after I had the MAF and upper boot off to give better access when replacing the alternator. I put a new upper boot on which I had on hand (chasing a 174 lean code). Lower boot is a year or two old, cleaned MAF with CRC.

Not that I am concerned about the actual guage reading, but I think it is an indication that something is not correct under the hood.

Anyone find the source of this problem?

Thanks
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  #8  
Old 09-20-2013, 11:25 AM
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mjalloul11 mjalloul11 is offline
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Re: MPG gauge creeps upon braking

As doru said. It is working corect. There are no vacume tube to the cluster it is all electric.

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  #9  
Old 09-20-2013, 12:18 PM
chevl71 chevl71 is offline
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Thanks. This symptom appeared the same time an idle issue appeared. I thought this could have been the cause. Hadn't seen the gauge react like this before.
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  #10  
Old 09-20-2013, 12:23 PM
cn90 cn90 is offline
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In other countries, it is measured by volume/distance such as L/km.

In this convoluted US country, we use mpg, so when the car stops at red light, the car travels 0 miles/h, thus 0 mpg on the gauge, basic math.
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  #11  
Old 09-20-2013, 01:02 PM
edjack edjack is online now
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Mein Auto: '97 540i 6 speed
Same gauge, different calibration. The two fuel consumption measurements are inversely related.

Watch the MPG gauge when decelerating. It moves all the way to the the left, which is "undefined," or "infinity," because the car is moving w/o fuel (the injectors are turned off during deceleration with the foot off the gas pedal; therefore, gallon is zero).

The gauge receives MPH and injector pulse width inputs.

Lobby your Congressmen to convert to the metric system.
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  #12  
Old 09-26-2013, 08:50 AM
chevl71 chevl71 is offline
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Thanks everyone. This makes more sense now.
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  #13  
Old 09-26-2013, 01:04 PM
poolman poolman is offline
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Mein Auto: 525i station wagon
I watch mine all the time to help get the best mileage possible--easy on the gas peddle and the needle moves slightly to the righ--heavy on the peddle the more it goes to the right along with more gas through the engine.
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