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Thread: False knock and how to get rid of it?

  1. #1
    Advanced Tuner Ghostnotes's Avatar
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    False knock and how to get rid of it?

    Been running into a bunch of false knock going into WOT and during WOT. Just found out these are notorious for doing this. I know you can turn the so called gain down on them slightly. I'm showing 12*KR sometimes under low RPM/high load conditions. I'm trying to run ~ 12 degrees but it gets smacked down to around 6. PE is dialed in 11.9-12.2 and my torque is about 70% done but i can't go any further till i get this settled down.

    Any help would be appreciated.
    I always tune VVE....
    2016 C7 M7 Z51
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  2. #2
    Senior Tuner Higgs Boson's Avatar
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    What are your mods?
    First thing to do is max out your knock sensors and lower the spark to 6 and see if it disappears then you know your knock sensors are reading knock and pulling timing.
    Next find out why they are sensing so much knock, maybe due to mods. Usually false knock will be evident at other than WOT also though. if it goes away with them off the they are sensing other sounds or you can try race gas with more spark to see if it is actual knock.

    Next what is your injector pulse width? If it goes too high you can see spark retard also.

    And of course the torque model could be to blame if it does not go away with knock sensors turned off and/or running race gas.

  3. #3
    Advanced Tuner Ghostnotes's Avatar
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    Quote Originally Posted by Higgs Boson View Post
    What are your mods?
    First thing to do is max out your knock sensors and lower the spark to 6 and see if it disappears then you know your knock sensors are reading knock and pulling timing.
    Next find out why they are sensing so much knock, maybe due to mods. Usually false knock will be evident at other than WOT also though. if it goes away with them off the they are sensing other sounds or you can try race gas with more spark to see if it is actual knock.

    Next what is your injector pulse width? If it goes too high you can see spark retard also.

    And of course the torque model could be to blame if it does not go away with knock sensors turned off and/or running race gas.
    2017 C7 Z51
    V7-YSi
    Large Cam,springs etc..
    2'' Headers
    Callies ultra Billet Rotating assembly.
    Stock injectors
    32% fuel lobe

    My duty cycle is around 20% and 5ms PW

    What tables to I max out and how?

    I started out with 6* and figured that was toooo low for a V7 so I added some back, either way the characteristics are the same. And I am getting it in other areas than WOT as well.If i keep my exhaust closed and stab it under a low engine speed/high load condition I get it. If i'm getting enough knock to cause 12*KR i should be able to hear that.At least i have in other vehicles with that much.

    I wouldn't put it past the torque model, it still needs a little work. My max and peak torque are working well together. My Driver Demand Says above my Commanded Axle Torque unless I'm decelerating.

    I don't have any readily available race gas, so I figured i would try to see if i can turn down the sensitivity a bit.


    Apparently this is a well known issue....have to fast forward a bit.

    https://www.youtube.com/watch?v=00P7...8gIZdOuSmdt5jD

    Thanks!
    I always tune VVE....
    2016 C7 M7 Z51
    Callies ultra billet crank
    Callies ultra billet rods
    Diamond pistons
    Jhonson high speed lifters
    Ported and polished headwork
    Custom cam
    YSi-V7

  4. #4
    Senior Tuner Higgs Boson's Avatar
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    Your PW is good so no worries there, just something I like to rule out early.

    The knock sensor settings are under Spark -- Knock Sensors then there are 8 tables (1 per cylinder) and you can max those tables. Don't leave it like this as you want them to work, but this will tell you if the retard activity is coming from them. If it is really you will need to get a knock box and listen for knock with headphones and tailor your knock sensors to match while you find MBT on a dyno.......

    How far you want to take that is up to you and how much time, patience, etc you have.

    If you disable them and still show all that retard then you have a torque model issue.

    edit: clicked your link and yes, that is the kind of knock box I am referring to. :-)

  5. #5
    Advanced Tuner Ghostnotes's Avatar
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    Yeah i was expecting a lot more duty cycle as well.
    I was figuring on those tables, just put them to a high value. So no need to do anything in the spark retard section i guess.This will definitely help me be able to eliminate weather it's torque or not. Going to try to change my PE ramp rate as well.

    Oh i have plenty of patience. Been working on this build for 6 months with everything included. Another weekend or 2 is no big deal.
    I used to have a knock box years ago but sold it when i got out of engine building for a living.

    After all of this....torque tuning seems to be the easy part.Hardest part for me was idle tuning and costdown.

    Here is a screenshot

    I think that spike in my CMD Axle torque is wheelspin but the rest of it seems to be inline with most of what i have read/learned.

    Another thought, even though im a manual, could the traction control/torque mgmt side be kicking in as well...i forgot to think of that till just now.
    Attached Files Attached Files
    Last edited by Ghostnotes; 01-20-2019 at 10:28 AM.
    I always tune VVE....
    2016 C7 M7 Z51
    Callies ultra billet crank
    Callies ultra billet rods
    Diamond pistons
    Jhonson high speed lifters
    Ported and polished headwork
    Custom cam
    YSi-V7

  6. #6
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    Direct injection engines are like Diesel engine - only small window for fuel , so duty cycle doesn?t madder
    Pulse width up to 6.5 is ok and when that?s maxed out - u need more fuel pressure for fuel

    Ps 12 degrees of knock. =. Boom
    Last edited by paulsmithsr; 01-20-2019 at 06:40 PM.

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    Quote Originally Posted by paulsmithsr View Post
    Direct injection engines are like Diesel engine - only small window for fuel , so duty cycle doesn?t madder
    Pulse width up to 6.5 is ok and when that?s maxed out - u need more fuel pressure for fuel

    Ps 12 degrees of knock. =. Boom
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  8. #8
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    Read above

  9. #9
    Advanced Tuner Ghostnotes's Avatar
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    Quote Originally Posted by paulsmithsr View Post
    Direct injection engines are like Diesel engine - only small window for fuel , so duty cycle doesn?t madder
    Pulse width up to 6.5 is ok and when that?s maxed out - u need more fuel pressure for fuel

    Ps 12 degrees of knock. =. Boom
    I think I'm still fine on fuel. I'm only have a 3psi difference. I took out 10% in the tables and it pretty much went away. Besides enough knock to cause 12* would be audible when the exhaust is in quiet mode in low rpm conditions which is where it's also happening.
    I do plan on verifying it though...

    I still need to work on the torque a little more. I logged my 2018 CT-6 and at WOT, the TPS and pedal was almost a 1:1 ratio. 90% pedal was met with ~90% throttle. I can only get to about 68% on my C-7.
    I always tune VVE....
    2016 C7 M7 Z51
    Callies ultra billet crank
    Callies ultra billet rods
    Diamond pistons
    Jhonson high speed lifters
    Ported and polished headwork
    Custom cam
    YSi-V7

  10. #10
    Senior Tuner Higgs Boson's Avatar
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    Quote Originally Posted by Ghostnotes View Post
    I think I'm still fine on fuel. I'm only have a 3psi difference. I took out 10% in the tables and it pretty much went away. Besides enough knock to cause 12* would be audible when the exhaust is in quiet mode in low rpm conditions which is where it's also happening.
    I do plan on verifying it though...

    I still need to work on the torque a little more. I logged my 2018 CT-6 and at WOT, the TPS and pedal was almost a 1:1 ratio. 90% pedal was met with ~90% throttle. I can only get to about 68% on my C-7.
    make sure you are logging the right pids

  11. #11
    Advanced Tuner Ghostnotes's Avatar
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    I am I made sure they both were 1 to 1

    The layout in the post above is what I'm using to scan both. The only difference is the WB values are dead cause the caddy has no wideband. I put out a shout locally to see if anybody has a "knock box" as we used to call them. Surprisingly most the local tuners don't use it.

    I am however seeing a little in my shift transitions because I'm going way lean.
    I always tune VVE....
    2016 C7 M7 Z51
    Callies ultra billet crank
    Callies ultra billet rods
    Diamond pistons
    Jhonson high speed lifters
    Ported and polished headwork
    Custom cam
    YSi-V7

  12. #12
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    Quote Originally Posted by paulsmithsr View Post
    Direct injection engines are like Diesel engine - only small window for fuel , so duty cycle doesn?t madder
    Pulse width up to 6.5 is ok and when that?s maxed out - u need more fuel pressure for fuel

    Ps 12 degrees of knock. =. Boom
    lol ok guy.
    ---------------------------------
    Keep in mind, with most GDI setups, the first line of defense is to pulling timing, or show KR. This is telling you that something else is out of line from what the engine wants. As a small test, you can soften up the knock sensors and drop the timing to to make sure it isn't the typical "gm riding the knock sensor" situation.
    The most hated, make the most power.
    93 Ranger. 5.3 D1X. 1069hp.

  13. #13
    Advanced Tuner Ghostnotes's Avatar
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    Quote Originally Posted by Area47 View Post
    lol ok guy.
    ---------------------------------
    Keep in mind, with most GDI setups, the first line of defense is to pulling timing, or show KR. This is telling you that something else is out of line from what the engine wants. As a small test, you can soften up the knock sensors and drop the timing to to make sure it isn't the typical "gm riding the knock sensor" situation.
    I did, I took 10% of total math out of the knock sensors and it went away. But I'm pretty sure I'm safe because during my shifts, my lambda is going to 1.17 and I'm getting ~1-2* retard which lines up perfectly with my lean spike, it literally completes the loop.

    I'll post a screenshot today when I get off, I forgot tot last night.
    I always tune VVE....
    2016 C7 M7 Z51
    Callies ultra billet crank
    Callies ultra billet rods
    Diamond pistons
    Jhonson high speed lifters
    Ported and polished headwork
    Custom cam
    YSi-V7

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    Left field here, I know you mentioned it. What is your fuel pressure doing. What is it commanding? vs actual? What is the LPFP doing pressure wise? Ran into a similar issue on a c7z with an f1a on it. The lpfp was falling offer at 4500 causing some fun issues.
    The most hated, make the most power.
    93 Ranger. 5.3 D1X. 1069hp.

  15. #15
    Advanced Tuner Ghostnotes's Avatar
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    Ill double check but I was only logging LPFP and I THINK it was 55ish at idle and 52ish at WOT. I know for sure I was only losing about 3psi above 4k but steady.
    I always tune VVE....
    2016 C7 M7 Z51
    Callies ultra billet crank
    Callies ultra billet rods
    Diamond pistons
    Jhonson high speed lifters
    Ported and polished headwork
    Custom cam
    YSi-V7

  16. #16
    Advanced Tuner Ghostnotes's Avatar
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    Ok so my fuel pressure ranges to around 45psi in cruise and spikes to about 75psi at WOT.Obviously you can tell if you are losing HSFP by losing too much LSFP...so what is not enough?

    Here is a shot of the pull.

    Either something is holding my throttle closed and i have a lot more power to gain, or im only getting what i need....
    Attached Files Attached Files
    I always tune VVE....
    2016 C7 M7 Z51
    Callies ultra billet crank
    Callies ultra billet rods
    Diamond pistons
    Jhonson high speed lifters
    Ported and polished headwork
    Custom cam
    YSi-V7

  17. #17
    Advanced Tuner Ghostnotes's Avatar
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    Thoughts^^^
    I always tune VVE....
    2016 C7 M7 Z51
    Callies ultra billet crank
    Callies ultra billet rods
    Diamond pistons
    Jhonson high speed lifters
    Ported and polished headwork
    Custom cam
    YSi-V7

  18. #18
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    You're not losing enough from the lpfp to cause the issue i was having. another left field shot. Injection timing wonky?
    The most hated, make the most power.
    93 Ranger. 5.3 D1X. 1069hp.

  19. #19
    Advanced Tuner Ghostnotes's Avatar
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    Just got my cam timing data today from TSP. You can do the math but i wanted to be sure. Going to check it against the table to see. Doubt that is closing the blade directly.Most of my torque looks pretty inline but my VT needs a little more now. My 2 biggest issues is sill coastdown and cold start. It starts right up but untill it gets really warm it's a little rough. Will work on that Sunday then VE.

    Wish me luck on that......
    I always tune VVE....
    2016 C7 M7 Z51
    Callies ultra billet crank
    Callies ultra billet rods
    Diamond pistons
    Jhonson high speed lifters
    Ported and polished headwork
    Custom cam
    YSi-V7

  20. #20
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    Quote Originally Posted by
    Apparently this is a well-known issue....have to fast forward a bit.

    [url
    Yes, this is quite a resource. Thanks
    Last edited by Catie; 04-09-2020 at 02:30 AM.