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Thread: Knock Sensor DTC ???'s

  1. #1
    Lifetime Member GAMEOVER's Avatar
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    Question Knock Sensor DTC ???'s

    Stock Camaro T-56 & 2004 5.7 LS1 in a 1993 RX7...
    If knock sensors were not connected(Knock sensor DTC were there) during a 1/4 mile pass...What would LS1 pcm do?
    Would it automatically default to low Octane table? What else? There is no power after 2500 RPM...I'm 99% positive that was culprit for low power...Just after some info...
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    Lifetime Member Boost's Avatar
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    I looked at "action taken" by the PCM for all the knock sensor related codes and did not see any indication that it would reduce power further that defaulting to the low octane table. I assume this is what you mean by "no power". There is quite a drastic difference there so I'm not suprised. Sounds like an easy fix.
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    Lifetime Member GAMEOVER's Avatar
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    I agree that it's pretty drastic going from a Tuned High Octane Spark table down to the Low Octane Spark table...but what I want to know is if thats all that happens when Knock sensor DTC's are present...
    2008 2WD Ext.Cab Silverado 1500 6.0 V-MAX E38(L76) & T42(4L70E) MAF Only CL Corvette Servo AFE CAI INNOVATIVE LM-2 WBO2

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    Lifetime Member Boost's Avatar
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    Yes, that's what I meant. No further action is taken other than a MIL.
    TORQUE SOUTH Tuning 125 VINs programmed
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    Member ippielb's Avatar
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    The knock sensor responds to spark knock caused by Pre-detonation of the Air/Fuel mixture. As the flame front moves out from the spark plug ignition point, pressure waves in the chamber crash into the piston or cylinder walls resulting in a sound known as a knock or ping. This is caused by using a fuel with a low octane rating, overheating, or over advanced timing. Sometimes it can be caused by hot carbon deposits on the piston or cylinder head that raise compression. A knock sensor is comprised of Piezoelectric materials; Crystals that when impacted, generate a voltage (same idea as a BBQ ignitor). This voltage is monitored by the computer, and when an irregularity is detected, the computer corrects timing in VVT (variable valve timing) engines, or triggers a DTC Diagnostic Trouble Code) in older vehicles.

    Read more: http://wiki.answers.com/Q/What_does_...#ixzz1N24uBya0
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    Joe (Moderator) joecar's Avatar
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    I read someplace that any knock sensor failure/DTC defaults the PCM to the LO table.

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    Member ippielb's Avatar
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    Quote Originally Posted by joecar View Post
    I read someplace that any knock sensor failure/DTC defaults the PCM to the LO table.
    This is correct, knock sensor failure puts you into the lowest octane table you have. Going from a tuned high octane table to a low table you will feel absolutely gutless.

    Knock sensor replacement on LS1 engines are a pain. They're located UNDER the intake manifold. There is two sensors in two identical indentations on the top of the block. Moisture gets under the intake manifold and settles in those indentations and rusts the knock sensors. By bad design on GM's part.

    To replace the senors remove your intake manifold, and pop off the two rubber grommets that are on the top of the block, there should be one wire coming out of each.

    There's going to be a plastic connection that connects to the top of the knock sensor. I would highly recommend purchasing two new pigtails. 90% of the time they break during removal. Easy to replace, cut the wire crimp the two wires together from the pig tail to the stock wire, heat shrink it water tight.

    To remove the knock sensor just take your ratchet and socket and unscrew from the block.


    Then when doing the installation, be sure to use rtv silicone to seal the grommet water tight and air tight.
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    Member ippielb's Avatar
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    Here's some real pictures from an 02' 5.3l that had knock sensors replaced.

    Intake Manifold Removed



    One of the knock sensors

    The other, you can tell why it doesn't work anymore. See the plastic from the broken connection during removal.


    Both knock sensors removed


    Connections on the knock sensors themselves rusted.


    The block, lots of moisture in there rusted.
    2002 Chevrolet Silverado 1500 z71 __ Lifted 7" __ AirAid Cold Air Intake __ AirAid PowerAid Throttle Body Spacer __ Pacesetter Long Tube Headers __ True Dual Exhaust FlowPro Mufflers __ MSD Ignition Plug Wires __ Flex-A-Lite Dual Electric Fan __ 4.56 Gears

  10. #10
    Member ippielb's Avatar
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    New knock sensor wiring harness


    New knock sensors installed with the harness hooked up


    Silicone job on the grommet


    All said and done, with a little more insurance on the top of the grommet.
    2002 Chevrolet Silverado 1500 z71 __ Lifted 7" __ AirAid Cold Air Intake __ AirAid PowerAid Throttle Body Spacer __ Pacesetter Long Tube Headers __ True Dual Exhaust FlowPro Mufflers __ MSD Ignition Plug Wires __ Flex-A-Lite Dual Electric Fan __ 4.56 Gears

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