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Thread: Knock on stock spark tables

  1. #1
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    Knock on stock spark tables

    I am having issues with knock on 91 pump gas with the stock spark tables on a 2018 gmc sierra 5.3 l83 A6 . Im honestly puzzled by it and am wondering if it's due to the lt4 injectors and lt4 fuel pump. It only happens under low rpms/high load. 3rd gear and up between 1100-1400 rpms when the engine is lugging for power. I've had to put negative timing to combat it. On the highway at 60mph I'm at 1150-1200 rpms. If i accelerate it will knock from 1100 rpms to 1400 rpms unless I make the truck downshift then there's no problem. If I run e85 I have no issues with knock just on 91.

    What is going on? Any ideas? Is there anyway to increase the rpm at highway speed? I am pretty sure that would require new gears right?

    My tuner said it was bad gas when it first started doing it, but that's not the case because it happens everytime I fill up with 91.

    This was the tuners response about it "What happens is I bet you are in higher gear (4,5, 6th which has low tq multiplication) and lugging it which causes a high load low rpm issue with spark"
    Last edited by GMCfast; 4 Weeks Ago at 07:48 AM.

  2. #2
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    what mods?

    Yes you will be more likely to see KR with high loads in high gear.
    I've tuned a few things...

  3. #3
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    Headers,y pipe catless,catback,CAI,lt4 injectors and hpfp, ngk LTR6IX-11, and Taylor wires.

  4. #4
    Tuning Addict 5FDP's Avatar
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    Do you still have the torque converter locked in gears 1-4?
    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

  5. #5
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    Quote Originally Posted by 5FDP View Post
    Do you still have the torque converter locked in gears 1-4?
    I'll check shortly. What should the torque converter settings be at?

  6. #6
    Tuning Addict 5FDP's Avatar
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    Factory settings would have real world numbers and if it was disabled they would be maxed out at 318/317 for each gear.

    I disabled lock up in all lower gears and it's only enabled in 5th and 6th.
    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

  7. #7
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    Shift lock is disabled but in the apply/release tab under speed>normal> apply,release,5th apply,6th settings have been adjusted when compared to stock

  8. #8
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    Quote Originally Posted by 5FDP View Post
    Factory settings would have real world numbers and if it was disabled they would be maxed out at 318/317 for each gear.

    I disabled lock up in all lower gears and it's only enabled in 5th and 6th.
    Yes they are maxed for 1-3. 4th is not

  9. #9
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    You bring up a great point though. Im going to return transmission tune back to stock and see if it corrects the knock.

  10. #10
    knock sensors can be sensitive to catless long tubes. i would recommend running 93 octane as well. do a search for injection timing and knock as well.

  11. #11
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    Thank you for your input this problem sounds like a injection timing issue! I'm going to see if the transmission tune was causing it. If its not the transmission, the injection timing SOI will be my next step.

  12. #12
    you shouldnt be knocking on the stock spark map even on 91 in all reality. have you checked to make sure nothing is loose or rubbing? before changing anything with the injection timing, because i wouldnt adjust that until you have added spark advance where you want, then use the soi table to try to help if you see knock which is usually low rpm high map. at least that is where it was for me on my 2016. first thing i would do is to fill up with some 93 and see what happens to the knock. Bad fuel does happen from time to time.

  13. #13
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    I second the SOI tables! Seems like the GENv just knocks at cruising speeds? Don't beat yourself up over knock in the 1200-1600 rpm range if your just going down the road. If your whippin on it and its knockin then id address it... My bone stock, not tuned yet, truck would show knock randomly at those rpms while going down the highway at 55... SOI adjustments helped allot when I started adding timing. You'll want to up the numbers, don't be afraid to get to 320* or so in those areas.
    14 GMC sierra 5.3

  14. #14
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    Loading the stock transmission tune didnt do anything for the knock. I don't have access to 93 octane where I live. The fuel and maf are dialed in pretty spot on. So next I will try soi tables.

  15. #15
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    Headers and catless pipes on the GEN v's usually require the knock sensors to be desensitized a little bit. Nothing major but headers amplify sound wavelengths and the knock sensors can pick this up. If you increase SOI and you still get knock, you will likely need to adjust the knock sensors a little bit.
    I've tuned a few things...