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"cold" spark plugs and poor cold start/idle

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    #1

    "cold" spark plugs and poor cold start/idle

    I've been fighting horribly rough and rich cold starts and idling with the new turbo setup. I assumed it was due to the Miller system, but when I plugged in my old ECU with the sssquid tuning chip, it ran exactly the same. Prior to the turbo, that tune ran flawlessly with zero issues.

    I started racking my brain about what I had changed that would affect cold idle and cold start. The only thing I can think of is the spark plugs. I changed out the standard Bosch WR8LC plugs that are stock on the m30b35 for a set of NGK 5534/BPR7ES plugs, which were recommended by the 745i guys over on bf.c. But given that my motor is a high-comp m30b35 and not a low-comp m106, and that it runs m1.3 (no cold start injector) versus m1.1 (yes cold start injector) has me second-guessing my choice.

    Can a spark plug that is too "cold" cause poor cold starts and idles? I have to confess I'm not 100% sure what the term "cold" refers to, I just know I here ithe term used often with regards to spark plugs in turbo applications.
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    #2
    Cold versus hot refers to the heat range in which the plug will operate. Boosted application require a more vigorous or higher intensity spark due to increased cylinder turbulence. Basically a blown or boosted engine can blow out a spark plug under boost if the spark is not intense enough. I can't remember which way the terminology goes (hot versus cold) but that is a very basic explanation. It's been a long time since I've thought about this(last boosted car was in 2007) so if anyone else has more thoughts on this feel free to correct me if I've made a mistake
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      #3
      What are your AFRs during warmup when it is running poorly?

      One heat range colder on plugs is not a super big deal.
      Lorin


      Originally posted by slammin.e28
      The M30 is God's engine.

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        #4
        My AFRs under warmup are around 10, and I get clouds of rich, dark smoke out the back. Once the engine temp hits about 50C though it smooths out and runs great.

        And no it's not the temp sensor, I've tested it a dozen times and the ohm readings are perfect. Plus it only has 3k miles on it.

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