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Thread: help tuning knock sensors - 98 ls1 z28

  1. #1
    Tuner in Training jbliss15's Avatar
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    help tuning knock sensors - 98 ls1 z28

    i have a pcm4less tune which seems fine and i've had good luck in the past.

    i keep getting 4.0KR even at part throttle and it happens when the exhaust starts to get really loud.

    i have cheap chinese headers and SLP loudmouth exhaust its extremely loud.

    at wot it shows 20.5 adv with the 4.0KR. so 24.5adv max. doesn't seem like i should be getting any real knock especially running 92.

    at part throttle i didnt record the actual adv but it still is pulling 4.0 right when the exhaust gets loud.

    i put in brand new ac delco sensors and dorman harness. the sensors appear to be working just too sensitive? eventually i get codes for both sensors "low input"

    i bought HPTUNERS and it will arrive tomorrow, i want to desensitize them and play around with it and see if i can get it to stop pulling timing.

    24.5adv doesn't seem like it would even be a problem with 87 octane.

    obviously i don't want to crack one of these HE pistons.

    any advice?
    98 ls1

  2. #2
    Senior Tuner 10_SS's Avatar
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    First pull 5-10 degrees of timing out of the tables, see if you still get knock. This will tell you if it's real or false knock.

    I personally wouldn't desensitize sensors. Unless you have false knock, meaning you still get the same knock after pulling 5-10 degrees.
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  3. #3
    Tuner in Training jbliss15's Avatar
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    ok, good advice.

    24.5adv doesn't seem like a lot?
    98 ls1

  4. #4
    Senior Tuner 10_SS's Avatar
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    Quote Originally Posted by jbliss15 View Post
    ok, good advice.

    24.5adv doesn't seem like a lot?
    for 87 octane, 24 is alot yes. 92 octane, no. Anything above 0 is allot with 87.

    my stock LS3 ran:
    1500rpm around 14 deg timing with a little knock,
    3300rpm around 28deg timing at WOT, no knock
    5300rpm down to24deg, and I would get a little knocks here, about 1deg retard, just like you, with premo fuel.
    Last edited by 10_SS; 02-26-2020 at 01:28 PM.
    2010 Camaro LS3 (E38 ECU)
    Whipple 2.9L, 3.875" Pulley, kit injectors, supplied MSD Boost-A-Pump, stock pump
    LG Motorsports 1 7/8" Headers - No Cats, stock mid pipe with JBA Axle Back
    ZL1 Wheels/Tires

  5. #5
    Tuner in Training jbliss15's Avatar
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    Just went for a drive to the gym and anything past half throttle and I get 4kr.

    It's never more or less just 4.

  6. #6
    Senior Tuner Ben Charles's Avatar
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    I’m betting exhaust is touching somewhere

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  7. #7
    Tuner in Training jbliss15's Avatar
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    Yeah it probably is but I fixed two spots I could see... I had to take a notch out of the subframe by the drivers header and the little crossmember thing where the y pipe connects to the rest

  8. #8
    Senior Tuner Ben Charles's Avatar
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    Bingo... there is your knock then

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  9. #9
    Tuner in Training jbliss15's Avatar
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    I fixed the spots I can see? A lot of shit rattles on the car how bad does it have to be?

    The license plate rattles bad and maybe the exhaust in the back by the tips

  10. #10
    Tuner in Training jbliss15's Avatar
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    I just got under the car and I can't see anywhere the exhaust is touching or even more than 1/2 inch close to something

  11. #11
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    If you have P0327 or P0332 KS codes the PCM will pre-emptively pull the amount of timing in the Maximum KR vs RPM (PE) table when you enter PE. Which on a 98 F-Body calibration just so happens to be 4*. Try setting those 2 DTCs to No Error Reported and see if the KR goes away.

  12. #12
    Tuner in Training jbliss15's Avatar
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    i turned off codes and took away 8 degress of timing 2,000rpm and above for both high and low octane tables.

    i will test it out in a few mins when i pick my boy up from school.

    if it still goes -4 i'll look at desensitizing the sensors rather than disabling them
    98 ls1

  13. #13
    Tuner in Training jbliss15's Avatar
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    after pulling the timing it still giving me 4KR

    i turned off codes and got no KR.

    i think the sensors/harness is not working correctly.

    i routed the harness next to the coolant line thinking it would not get crushed there?

    the only thing it should hit is little pieces of foam that already had indents in them from the collant lines

    i put everything back to normal considering the timining tables. but i left the KR codes off.

    i will post my timing tables and maybe someone could just look at it and make sure all things considered its normal for 92 octane.

    after i tested WOT pull i had 25.0-25.5 advance at higher RPMS. seems fine???
    98 ls1

  14. #14
    Tuner in Training jbliss15's Avatar
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    98 ls1

  15. #15
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    FYI, turning off the KS codes does not turn off the KS functioning. I've seen over and over KS setting codes and still function just fine detecting real knock.

  16. #16
    Tuner in Training jbliss15's Avatar
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    Quote Originally Posted by 2xLS1 View Post
    FYI, turning off the KS codes does not turn off the KS functioning. I've seen over and over KS setting codes and still function just fine detecting real knock.
    Even if the sensors are grounded out on the intake somehow?

    I'm confused because I copied over the low onto the high octane table and I still saw 28adv at upper rpms with no audible pinging.

    The low octane table said 26 max.
    98 ls1

  17. #17
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    I doubt the sensors are grounded out. Is there a break in the insulation on the harness? Try this. With the engine idling and the scanner running lightly tap on the front of the cylinder head with a hammer and see if it shows KR?

  18. #18
    Tuner in Training jbliss15's Avatar
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    Quote Originally Posted by 2xLS1 View Post
    I doubt the sensors are grounded out. Is there a break in the insulation on the harness? Try this. With the engine idling and the scanner running lightly tap on the front of the cylinder head with a hammer and see if it shows KR?
    I'll try maybe tomorrow

    What if I over torqued the sensors?

    I was working too fast and forgot to actually torque the sensors to spec subconsciously I remember torquing them to what I could feel about 20lbs. Dumb....