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Thread: Tuning questions, knock related and cutout

  1. #1

    Tuning questions, knock related and cutout

    Not sure if the knock is causing the system to cutout, no idea if it functions that way. Basically running about 15psi, it starts to break up and I can also hear knock. Using MPscan, I think the highest it registered was .75, not sure if that is bad or not. I don't know what the range is for acceptable knock. However, I can hear what seems like knock, but the loudness of it seems like I would be registering 2.75 KNKV. It may be valves(?), but I don't know and given that the noise increases with boost makes me think it's knock and not vavletrain.

    I've taken some timing out of the warm full throttle, but it seems like the 'knock' persist. Any ideas where to start? Was planning to take it to a dyno tomorrow, but don't want to waste the time or money if I can't take care of this first.
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  2. #2
    turbo addict
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    Re: Tuning questions, knock related and cutout

    Knock table is 0-5 volt. Above ~ 3,200rpm, .75 voltage is not consider a knock.
    What plugs are you using? You wanna send me your calibration so I can take a quick look? You have my number.


  3. #3
    Moderator Turbo Mopar Staff Force Fed Mopar's Avatar
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    Re: Tuning questions, knock related and cutout

    Wideband reading? Also, sounds silly but look for loose brackets that might be rattling against the bolt or frame. Breaking up would seem to point to the ignition system firt though, unless you're running really lean.
    Rob M.
    '89 Turbo GTC

    2.5 TIII stroker, 568 w/ OBX and 3.77 FD

  4. #4
    turbo addict
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    Re: Tuning questions, knock related and cutout

    Are you logging the RET1 - RET4 that will show if the computer is sensing knock and pulling timing. There is also a KNKACTV
    Or something close that indicates knock is sensed. Also some trouble codes will cause weird cutout issues as a limp mode attempt. Try changing your knock sensor.

    Other random ideas: Like mentioned above I had things rattle, as far as I know knock doesn't do anything that causes cutout. I have had bad spark plugs cause breakups.

  5. #5
    Slugmobile & MeanMini Caretaker Turbo Mopar Contributor wheming's Avatar
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    Re: Tuning questions, knock related and cutout

    If you have any pipe dope or teflon tape on the knock sensor threads, you could be reducing the knock sensing (and thereby reading a lower knock voltage when there is actual knock present).
    The sensor is only looking for knock near the firing events. That is why doing that knock sensor test doesn't spike voltage every time you tap the intake. You need to do somr quick rapid taps to see the knock voltage spike occasionally durjng the test.
    So, it is possible you have some kind of ambient noise that isn't knock, or if the noise onlu happens in boost, it could be you have a de-sensitized or bad knock sensor.

    I agree, that if it is breaking up there is something amiss with ignition. Bad plug gap, bad plug, bad wire, bad coil, or soething else.
    Be safe if you do decide to dyno, but you should probably not if it isn't running right. Don't waste the money.
    Wayne H.

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