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Thread: LS1 - LS2 Knock Sensor tuning

  1. #1
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    Default LS1 - LS2 Knock Sensor tuning

    I've searched and think I understand the basics of how/when/why to use which sensors with which controllers/engines. However, I haven't been able to find the answer to retuning for my combination.

    I have a 2004 Cadillac CTS-V that came with an LS6. I've replaced the block with an LSA block. Using a wire harness extension I now have the LS1/6 single wire knock sensors mounted in the side of block LSA location (with larger, re-tapped holes for the sensors). With the sensors moved from the valley to side of block location what should I be looking at changing in the tune?

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    Lifetime Member johnv's Avatar
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    I plan on doing something similar, in for info.
    Back yard boost
    347+ T76 = 770 rwhp 10.96 @ 135 mph

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    Joe (Moderator) joecar's Avatar
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    This is a hard thing to accomplish... it requires a spectrum analyzer (most serious USB/PC oscilloscopes can do on-the-fly FFT) and a means to cause real knock so that it can be analyzed... you have to find the central frequency and the typical amplitude of various real actual knock occurrences... maybe it can be done with knock phones on the dyno, but simultaneously you still need an FFT oscilloscope.

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    Lifetime Member johnv's Avatar
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    What about LS2 sensors with an LS1 PCM ?
    Have read that it can be done, but not much information out there..
    Back yard boost
    347+ T76 = 770 rwhp 10.96 @ 135 mph

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    Quote Originally Posted by joecar View Post
    This is a hard thing to accomplish... it requires a spectrum analyzer (most serious USB/PC oscilloscopes can do on-the-fly FFT) and a means to cause real knock so that it can be analyzed... you have to find the central frequency and the typical amplitude of various real actual knock occurrences... maybe it can be done with knock phones on the dyno, but simultaneously you still need an FFT oscilloscope.
    I do have access to a spectrum analyzer so I'll try this approach. Once I've got the central frequency where so I go in the tune?

    As for the question of using LS2 sensors I found the following over on the ls1gto forum:

    The reason the LS2 style sensors "dont/won't" work on an LS1 based system is because the LS1 PCM is not designed to work that way. The LS1 KS's are a single wire broadband sensor that the PCM sends a certain amount of voltage to, as the sensor detects knock, it changes the voltage reading and the PCM then knows how much knock is present by the amount of feedback voltage change.

    The LS2 sensors on the other hand, are what is known as a two wire "flat response" sensor. These style knock sensors actually send an AC voltage signal (similar to a wheel speed sensor) back to the PCM to record knock, no voltage "from" the PCM is needed, they create their own. The newer PCMs are also capable of learning and determining from the flat response sensors what is normal and what is not.

    So, to me anyway, it's pretty much black and white why an LS2 style sensor cannot be used on an LS1 system.
    I did find several articles/posts on how to rewire harnesses so that the LS2 sensor can be physically connected to an LS1 PCM but it doesn't seem that the actual algorithms in the PCM can properly process the signal so there is no value in pursuing this approach.

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    Joe (Moderator) joecar's Avatar
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    Quote Originally Posted by ronrath View Post
    I do have access to a spectrum analyzer so I'll try this approach. Once I've got the central frequency where so I go in the tune?

    . . .
    Depending on the tune, the tables are self evident (let me go a look thru my tune files...)

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    I just found this thread, and is quite an interesting subject
    I make and modify many LS1 wiring harnesses here in Oz for conversions, and many are LS1 harness and ecu's controlling LS2 and L98, LS3 engines
    In EFI Live there is an option for LS1 or LS2 knock sensors, with a description there explaining how to repin the existing 2 LS1 wires to X1- 09 & 10, and adding the other 2 Ground wires to X1 - 49 & 50, so one would assume Blacky has added the required logic.
    Coincidentally, this morning I rang VCM Suite ( HP Tuners) in Australia, asking them the very same question, as I have a customer that I am doing a L98 / LS1 harness for that will be tuned using HP Tuners, and as i have this software as well, I checked the function in that, which has both options, but no explanation of changing wiring pinouts, so thats why i rang them.
    The guy there told me you just earth the other ground wire to the block and use the 2 existing LS1 wires for the signals and the "ecu works it out".......
    I reckon good luck on that one....., I have done this before with EFI Live, but I got no Knock signals, but also got no Knock fault as well, and as i tune with a knock box, i can hear the slightest detonation and work with that anyway.....
    Does anyone know the real answer, and that is does either of these setups work with LS2 knock sensors.
    Another option is to use the V6 Ecotech knock sensors, as they screw directly into the existing threaded holes in the side of the block and use the single wire plug same as LS1

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    Joe (Moderator) joecar's Avatar
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    Quote Originally Posted by Hooter View Post
    ...
    In EFI Live there is an option for LS1 or LS2 knock sensors, with a description there explaining how to repin the existing 2 LS1 wires to X1- 09 & 10, and adding the other 2 Ground wires to X1 - 49 & 50, so one would assume Blacky has added the required logic.

    ...
    As far as I know, it is only a setting in the tune file (it does not write any logic into the tune file).

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