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Thread: E60 Alternator voltage Fluctuate at idle and Idle bounce.

  1. #1
    Join Date
    Aug 2017
    Location
    ireland
    Posts
    1
    My Cars
    e60

    E60 Alternator voltage Fluctuate at idle and Idle bounce.

    Hi All,

    This may be a well known issue in 2006 BMW 523i N52 engine , or similar models.

    ISSUE: Idle Fluctuate between 640 - 680, More often on engine operating temperature. while stoping at stoplight car shake little bit, rmp drop to ~630 for couple of sec and then raise up to normal. And then idle fluctuation continues.

    DIAGONOS AND OBSERVATIONS:

    1. Vacuum leak test - No Vacuum leak identified. Replaced new oil separator and hose, new Intake manifold gaskets, new throttle body gasket.
    2. Vanos test - Tested the Vanos in INPA, nothing strange. Swapped Intake and Exhaust vanos solenoid. still nothing changed.
    3. MAF sensor test - MAF reading 2.8 - 3.2 g/s at idle which fluctuate up and down waveform the MAF reading graph up and down match with the idle rpm up and down. SHOULD MAF READING BE STADY AT IDLE? , or IT CAN FLUCTUATE BETWEEN 2.8 - 3.2 AT IDLE?

    4. **** Battery Charging system Test :
    - Now while testing the Battery charging system something which I am not certain about. I hope You guys can clarify me.
    - While engine at idle the battery voltage is between 14.7 15.0v .
    - In INPA the the DME Voltage Supply and Battery Voltage Fluctuate between 14.40 to 14.90 and this fluctuation match with the idle engine rpm up and down between 640 - 670 . Please check the video attached.
    - ***But the most strange thing which I noticed. At idle there is sudden dip in the DME voltage supply value from 14.60 to 12.60 for couple of second and again raise up. Along with it the idle rpm also dip to around 600 rpm for couple of second and raise up. Please check the video attached. IS THIS VOLTAGE FLUCTUATION from 14.60 - 12.60v with IDLE DIP AND RAISE NORMAL?
    - Checked the alternator belt - fine. Alternator positive terminal- Good and clean. But.. There is a single pin harness connector connected at the back of the alternator, Guess it is to the voltage regulator. While ignition ON, i checked the input voltage on this connecter, it was only ~6.80 - 7.10 . WHAT IS THE CORRECT VOLTAGE ON SINGLE WIRE PIN ALTERNATOR REGULATOR HARNESS CONNECTOR ?





    I Hope some one could help me. I love this car, but this idle fluctuation making me mad for last 1 month.

    Thank you.

  2. #2
    Join Date
    Nov 2017
    Location
    hong kong
    Posts
    2
    My Cars
    2005 BMW 330i
    I have the same situation as you got, now I am prepare to do the voltage drop test with load on all major conjunction point and see if there is any loosen bolt, in the mean while, I am planning to swap my alternator(already bought one from ebay), coz I found that my alternator seems go weak(if there is no loosen bolt), only got 13.8v on average, and checking some of my friends e90 330i, their car is more stable and with at least 14V on idle, so I am going to do the alternator swap when weather is good and get back to you on my findings.

    also, I will do the fuel system cleaning, coil pack + sparkplugs replacement, my Long Term Fuel Trim detects the car is running rich, probably due to the spark is not strong enough with weak alternator.

    After all changes, I will need to do the ECU adaptation reset and see if any improvement on the result.

  3. #3
    Join Date
    Sep 2016
    Location
    Germany
    Posts
    83
    My Cars
    2004 BMW 530d
    I have similar symptoms, it's most likely the alternator.
    I will change not the whole thing but rather the regulator which very often goes bad.
    Will have something to report in a couple of weeks at the latest.

  4. #4
    Join Date
    Nov 2017
    Location
    hong kong
    Posts
    2
    My Cars
    2005 BMW 330i
    Quote Originally Posted by yeukfung View Post
    I have the same situation as you got, now I am prepare to do the voltage drop test with load on all major conjunction point and see if there is any loosen bolt, in the mean while, I am planning to swap my alternator(already bought one from ebay), coz I found that my alternator seems go weak(if there is no loosen bolt), only got 13.8v on average, and checking some of my friends e90 330i, their car is more stable and with at least 14V on idle, so I am going to do the alternator swap when weather is good and get back to you on my findings.

    also, I will do the fuel system cleaning, coil pack + sparkplugs replacement, my Long Term Fuel Trim detects the car is running rich, probably due to the spark is not strong enough with weak alternator.

    After all changes, I will need to do the ECU adaptation reset and see if any improvement on the result.

    For me, I have just changed the entire alternator today, and the result is +VE, my car finally response aggressively and rev up much faster than before, the fuel trim value is always -ve (too much fuel detected) to now always +ve, which probably i got some vacuum leak somewhere, need to do smoke test later of time.

    the REV is now around 670rpm steady, in inpa, it read as 640 rpm steady.

    For the voltage drop, i have run for 20minutes using torque, and the voltage has never been that steady, must not drop over 13.8V, and sometimes saw 14.6V several seconds, in before, my alternator just the same as yours, sometimes drop to 12.6V for few seconds, which also trigger the idle speed run up at 800rpm if DME detects the car is draining power from battery.
    Last edited by yeukfung; 01-11-2018 at 08:03 AM.

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