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  1. #1
    Join Date
    Nov 2016
    Location
    Wanganui New Zealand
    Posts
    10
    My Cars
    2003 X5 4.6is

    2003 x5 4.6is right hand bank fouling plugs on start up

    Please help.. I have spent days trying to find a solution... Reading thread after thread but nothing seems to quite fit my problem.
    The x5 has one black tail pipe and one clean one.. It also has a slightly rough cold start with light black bearly visible smoke coming out of the right exhaust.
    The x5 has all new coils and plugs but the right hand bank are all completely black and the left-hand all perfect.
    Both banks have leaking valve covers and the oil separator has a bit of milkly mayo in it
    The x5 runs fine apart from the cold start and revs beautifully and pulls cleanly.
    If I swap a clean plug from the left to the right it will turn black from one single start up.
    I have cleared the oil out of the banks until the valve cover gaskets arrive..
    If I bang hard on the cats they are solid with no noise.
    A new oil separator and CCv are on the way along with a timing chain tensioner due to a rattle on first start up in the morning.
    What would cause one bank (every single plug) to foul instantly?
    It appears to be carbon rather than oil.. There appears to be no obvious vacuum leak detectable with brake cleaner.
    I have a obd2 cable on the way but can hear by ear little misses on the cold start cycle.
    Is there anything I'm missing that would obviously effect one entire bank but not the other.
    I think I can rule out cats as it revs nicely...
    Would the ccv effect one bank? Or would I see oil rather than carbon?
    Is there a sensor I'm missing that would make one bank rich enough to foul but no strong gas smell?
    Any suggestions would be appreciated

  2. #2
    Join Date
    Nov 2016
    Location
    Wanganui New Zealand
    Posts
    10
    My Cars
    2003 X5 4.6is
    would the secondary air injection effect one bank?

  3. #3
    Join Date
    Oct 2003
    Location
    Seattle
    Posts
    5,776
    My Cars
    99 M3

    2003 x5 4.6is right hand bank fouling plugs on start up

    How many miles and what is service history?


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    Last edited by bluptgm3; 12-21-2017 at 08:20 PM.

  4. #4
    Join Date
    Nov 2016
    Location
    Wanganui New Zealand
    Posts
    10
    My Cars
    2003 X5 4.6is
    149km.. sorry

  5. #5
    Join Date
    Oct 2003
    Location
    Seattle
    Posts
    5,776
    My Cars
    99 M3

    2003 x5 4.6is right hand bank fouling plugs on start up

    Is there a ‘Check Engine’ lamp illuminated? What are the codes?

    O2 sensors been changed @ 100k?

    Spark plug extenders replaced with plugs?


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    Last edited by bluptgm3; 12-21-2017 at 09:02 PM.

  6. #6
    Join Date
    Nov 2016
    Location
    Wanganui New Zealand
    Posts
    10
    My Cars
    2003 X5 4.6is

    Solved

    It's New Zealand new with a good service history from BMW up until the last couple of years as we don't have anyone locally
    My scanner arrived in the car was throwing a code for the pre cat oxygen sensor so I ordered a new one and in the meantime had a look with the intention of giving it a good clean until the new one arrived turns out the oxygen sensor wasn't even plugged in!!
    So I plugged it back in cleared all the adaptations and the car runs mint!!
    No more black smoke and the spark plugs cleared up after giving the car a decent run

  7. #7
    Join Date
    Oct 2003
    Location
    Seattle
    Posts
    5,776
    My Cars
    99 M3
    When you get around to replacing them, with this mileage it is probably best to replace both of them.


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  8. #8
    Join Date
    Nov 2016
    Location
    Wanganui New Zealand
    Posts
    10
    My Cars
    2003 X5 4.6is
    Quote Originally Posted by bluptgm3 View Post
    When you get around to replacing them, with this mileage it is probably best to replace both of them.


    Sent from my iPhone using Tapatalk
    Thanks for the advice
    Do you mean both pre cat o2 sensors or the pre and post cat on the fouled bank?

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