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Thread: 2004 2500hd tow rig knock issue

  1. 06-03-2020 #1
    CodyJohnson
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    2004 2500hd tow rig knock issue

    6.0 4l80e ccsb 4x4. I have replaced all knock sensors with new GM AcDelco units two times now, and the harness. Rang out the wiring and everything has been looking good. This truck is all stock, just ticked over 300,000 miles. I keep getting a pending knock sensor code, which was on during these logs, it always comes right back. Started logging right as the truck got to temp, and it seems like as the truck gets more heat, it starts throwing KR like crazy. Fueling and spark are stock, i have tweaked a few things in the tune, but nothing crazy. Stock spark and fuel... etc (PE was on and tuned with wideband, i reverted to stock fueling and spark for these logs)

    I'm leaning toward this being the cats plugged up, but from what i can see on the back side they look clear and not plugged up. Does anyone else have thoughts on this? FWIW i bought this truck after it got flooded out by previous owner, replaced the engine, and the exhaust was full of water. I have been driving this for 50,000 miles after all of that never had one issue. Again, the cats look OK from the back side. Any help or thoughts would be appreciated. Thanks


    2500 knock.hpl
    gimmer stock fueling.hpt
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  2. 06-03-2020 #2
    5FDP
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    Pending or current codes will cause it to max out the knock retard to the max value set in the tune, which is 8 degrees.

    You can disable the codes and it will stop this from happening. You can also still test the knock sensors with the codes disabled by smacking the block or somewhere on the engine with a rubber mallet, it should still pick up the "knock" when you do that.
    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

    If you don't post your tune and logs when you have questions you aren't helping yourself.
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  3. 06-05-2020 #3
    Hondaeater
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    You might start with an octane booster like Boostane to eliminate the bad fuel possibility. The fact your PE comes in at 65% TPS you have control of your ECT below 210. Make sure to log for misfires too.
    Last edited by Hondaeater; 06-05-2020 at 08:33 PM.
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  4. 06-06-2020 #4
    ryan_axberg
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    thats pretty funny calling a gas truck a tow rig, just had to throw that out there.
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  5. 06-15-2020 #5
    ticketmagnet
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    Quote Originally Posted by ryan_axberg View Post
    thats pretty funny calling a gas truck a tow rig, just had to throw that out there.
    Oh no, the world has already forgotten about big blocks!
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