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Thread: Spark swing by 20 degrees during light load takeoff

  1. #1
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    Spark swing by 20 degrees during light load takeoff

    hello, I have something confusing going on.

    light accel takeoff I can feel rpm swing a bit and see its due to timing bouncing around. no knock retard is happening.

    in the log I see its happening around 16mph, and 6mph so I dont think its idle timing.

    to make it easier to find the info in the tune, these are where it happens:

    it jumps from 12 degrees to 35 degrees at 17mph slight accell, and back and forth as seen in the pic. time in the log file is 5:33.266
    rpm-----g/sec-----actual timing------idle timing-----Main Timing
    965-----0.24 ------12 degrees-------17 degrees----33 degrees
    1047----0.23-------35 degrees

    another area going 7mph it showed -4 degrees then 22 degrees, idle spark is 13 degrees in this rpm/airflow.

    can anyone help??

    thanks
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    Last edited by 10_SS; 04-17-2012 at 06:40 PM.

  2. #2
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    come on.. no ideas here? Im used to LT1_Edit, Tunercats, and MEgasquirt and these by default have a "LED" indicator when PE, Knock, Idle, or really any other event is happening.

    With this RPM swing I dont see anything happening anywhere to trigger it, unless it's related to idle RPM control but this is moving.

    BTW it may be occuring when I'm slipping the clutch going into gears? I could probably include clutch position to check. But why?

    This worries me since it makes me think I really have no control over timing.

    Anybody?
    Last edited by 10_SS; 04-19-2012 at 12:04 AM.

  3. #3
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    Engine > Spark > Advance > General
    Set Spark Smoothing to disable.

  4. #4
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    Quote Originally Posted by Sam88gta1 View Post
    Engine > Spark > Advance > General
    Set Spark Smoothing to disable.
    Thanks I'll try it however the feature says it's there to dampen what I see. So confused. I can actually feel the engine oscillate that's why I looked at the log and found the timing doing it.

    "Spark Smoothing works to reduce rapid accellerations and decelerations of the engine to dampen drivetrain oscillations."

  5. #5
    Senior Tuner IDRIVEAG8GT's Avatar
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    Sam's right. Just disable it.
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  6. #6
    Advanced Tuner vette_c6's Avatar
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    to get an good answer ,, POST your file
    and your scanner log

    specialize in: V8 Tuning (Kuwait)
    Abdullah Al-najdi
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    Tuners ! Quit Raping your PE TABLE !

  7. #7
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    Quote Originally Posted by vette_c6 View Post
    to get an good answer ,, POST your file
    and your scanner log
    log and tune attached. The event in the pic above occurs around log# 6661.

    Thanks for the replies, yes I really do want to understand what GM/The ECU is thinking here since all code happens for a reason.

    You will also see the RPM surging a bit as a result of the timing swing.. this is why I thought IDLE rpm correction was trying to kick in but I dont think this anymore.

    Also, is there an indicator to enable to see when "this" is occuring? There's an indicator for every event in the simpler software. I know the newer ECU's are more complex but figured I'd ask.

    Could it be something trying to limit clutch slip?
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  8. #8
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    Are you running a MAF tune or SD? Does the rpm "hang" if you press the clutch while that oscillation is happening?

    I had a similar problem in my 08 LS3. I would get trailer-hitching/bucking at very light load in the low RPMs. Ended up chekcing for vac leaks (there were none), cleaning the TB (it was dirty) , and reducing the minimum airflow values (Engine> Idle>Airflow). Now its all smoothed out.

    Not sure if thats your problem but something to consider.

  9. #9
    Advanced Tuner vette_c6's Avatar
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    disable the spark correction
    and match the idle spark with your timing spark table ,, then post a scan

    specialize in: V8 Tuning (Kuwait)
    Abdullah Al-najdi
    00965 99369929
    www.youtube.com/alnajdi83
    Tuners ! Quit Raping your PE TABLE !

  10. #10
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    Quote Originally Posted by vette_c6 View Post
    disable the spark correction
    and match the idle spark with your timing spark table ,, then post a scan
    I disabled the "spark smoothing" and sure enough all of the spark swing/oscillation is gone! Huge difference! Feels so much smooth and normal. I also noticed the info box says this is for manual trans only.

    Thanks everybody! Disabling is a must have with a manual!

    Still wondering what it's suppose to do.. maybe stop some bucking at low rpm low gear like 10mph parking lot crawls if that was a problem? Maybe find a way to have it only active then and not when your taking off or releasing the clutch or accelerating from low rpm in low gears.

  11. #11
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    Are you using the latest Beta version of VCM suite? At some point Chris added parameters to control the Spark Smoothing feature.


  12. #12
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    yes I see those settings however I haven't noticed any negative side affects from having it disabled... only positives. I guess until I find out what it is intended to improve, I will leave it off.

  13. #13
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    Quote Originally Posted by vette_c6 View Post
    disable the spark correction
    and match the idle spark with your timing spark table ,, then post a scan
    Do not match your idle spark table with the high or low octane tables. Those tables are seprate for a reason and will cause you problems if they are the same value.

  14. #14
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    Quote Originally Posted by 10_SS View Post
    yes I see those settings however I haven't noticed any negative side affects from having it disabled... only positives. I guess until I find out what it is intended to improve, I will leave it off.
    There will never be a need for it to be enabled.

  15. #15
    Advanced Tuner vette_c6's Avatar
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    Quote Originally Posted by Sam88gta1 View Post
    Do not match your idle spark table with the high or low octane tables. Those tables are seprate for a reason and will cause you problems if they are the same value.
    your are 100% right
    these table is to move from your tune ,, to what i call safe mode
    which is decrease the timing ,, its always less then the high octain table

    but when you are tuning sometimes you need to match them ,, till you finish your tune
    you dont need any mess when you do your tuning ,,

    and its always a Tuner way how does he wanna tune ,,,
    your point is right and my point is right

    good luck

    specialize in: V8 Tuning (Kuwait)
    Abdullah Al-najdi
    00965 99369929
    www.youtube.com/alnajdi83
    Tuners ! Quit Raping your PE TABLE !