Results 1 to 14 of 14

Thread: Knock Learn In the E38 PCM

  1. #1

    Knock Learn In the E38 PCM

    So I've been trying to figure this out for a few hours and maybe its just best if I ask. When no knock is detected in the E38 is it 100% using the high octane table? From what I've read the pcm is always using a blend of both the high and low octane and just deviates more towards the low when knock over a certain amount is detected?

    That doesn't really make much sense to me as there would be no purpose of having a high table. I always thought the pcm would default to only the high octane table and if knock over the threshold in the tune was detected learn would kick in and it would begin to start to decay towards the low table.

    In other words if you command 23 degrees and it sees 3 degrees of KR and your threshold is 2 then it will begin to decay towards the low table. If it saw 1 though it would do nothing except pull timing momentarily then continue to use the high octane table as the threshold of 2 degrees had not been reached to begin activating the low tables

    Which is the correct method? Is it different in the e38?

    Also if you completely disabled knock learn ( set all enable values to max) would you essentially disable the low octane table?
    Last edited by 02pewterz28; 02-03-2017 at 03:46 PM.

  2. #2
    Senior Tuner 10_SS's Avatar
    Join Date
    Mar 2012
    Location
    Detroit, MI
    Posts
    1,320
    Quote Originally Posted by 02pewterz28 View Post
    So I've been trying to figure this out for a few hours and maybe its just best if I ask. When no knock is detected in the E38 is it 100% using the high octane table? From what I've read the pcm is always using a blend of both the high and low octane and just deviates more towards the low when knock over a certain amount is detected?

    That doesn't really make much sense to me as there would be no purpose of having a high table. I always thought the pcm would default to only the high octane table and if knock over the threshold in the tune was detected learn would kick in and it would begin to start to decay towards the low table.

    In other words if you command 23 degrees and it sees 3 degrees of KR and your threshold is 2 then it will begin to decay towards the low table. If it saw 1 though it would do nothing except pull timing momentarily then continue to use the high octane table as the threshold of 2 degrees had not been reached to begin activating the low tables

    Which is the correct method? Is it different in the e38?

    Also if you completely disabled knock learn ( set all enable values to max) would you essentially disable the low octane table?
    When Knock Learn states 0.00, then it is using 100% HIGH octane table, when Knock Learn reaches 1.0, then it reads 100% of the LOW octane table.

    So lets say your cruising along on 92 octane and you haven't had any knock in days, the Knock Learn should say 0.00. IN this case your getting full timing and motor feels pretty responsive.. you mash the gas and you get a blip of knock, not bad, but your knock learn incremented a bit to 0.09, well no big deal as now its gravitated 9% towards the LOW Octane table (0.00 = 0% and 1.00 = 100% Low Octane Table). Thing is, this Knock Learn table tends to rember where the knock occured, so will only apply this 9% in this load/rpm range the knock occured.. this "remembering where it occurred" could be debatable, but is the case a Dodge Hemi I looked at, and maybe not with my 2016 Silverado 5.3... not sure, but pretty sure. The silverado Knock Learn increments fast, and decays fast... (seconds to minutes to decay). Example if your towing on hot day, I get allot of knock steady state, that drives up the knock learn for given RPM and Load... then if I change gears or slow down and hit similer RPM/load, I will see that "phantom" knock learn pop up even though there is no knock...

    Then lets say the next day you messed up and put 87 in there, now it's knocking all the time, and your Knock learn is moving upwards of 0.65, you should be using 65% LOW Octane table.. then since your running less timing, you notice less knock, and you'll see the Knock Learn starts coming back down again usually pretty quick.

    This process repeats forever, or until you pull the batt cable, then the Knock Learn resets to 0. This is why some people seem to think pulling the batt cable makes it run stronger, because if you had allot of knock for whatever reason, it could have pushed your knock learn up high, and if you put 93 back in, it does take awhile for it to come back down to 0.
    Last edited by 10_SS; 02-03-2017 at 10:03 PM.
    2010 Camaro LS3 (E38 ECU - Spark only). MS3X running complete RTT fuel control (wideband).
    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

  3. #3
    Moderator
    Join Date
    Mar 2014
    Location
    Raleigh, NC
    Posts
    6,347
    Pretty much that's it.

    0 = high octane
    1 = low octane

    Starts at 0, increases every knock event (amount it increases depends on how much KR there is), then very slowly goes back down under certain conditions (MAP > 50kpa on my stock tune). Takes quite a while to work it's way down.. it's not like regular knock retard that drops out in second or so
    Post a log and tune if you want help

    VCM Suite V3+ GETTING STARTED THREADS / HOW TO's

    Tuner by night
    CPX Tuning
    2005 Corvette, M6
    ECS 1500 Supercharger
    AlkyControl Meth, Monster LT1-S Twin, NT05R's
    ID1000's, 220/240, .598/.598, 118 from Cam Motion

    2007 Escalade, A6
    Stock

  4. #4
    Is there a PID to watch the knock learn value?

  5. #5
    Moderator
    Join Date
    Mar 2014
    Location
    Raleigh, NC
    Posts
    6,347
    Yes. It's called knock learn

  6. #6
    Senior Tuner 10_SS's Avatar
    Join Date
    Mar 2012
    Location
    Detroit, MI
    Posts
    1,320
    Quote Originally Posted by schpenxel View Post
    Yes. It's called knock learn
    Where's the like button?
    2010 Camaro LS3 (E38 ECU - Spark only). MS3X running complete RTT fuel control (wideband).
    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

  7. #7
    Only one i could find was "Knock Learn Factor" I assume u mean that one.

  8. #8
    Moderator
    Join Date
    Mar 2014
    Location
    Raleigh, NC
    Posts
    6,347
    Yeah that's it

  9. #9
    Went from 87 octane to E85. How do I reset my knock learn? It seems to be taking weeks to do it automatically

  10. #10
    Moderator
    Join Date
    Mar 2014
    Location
    Raleigh, NC
    Posts
    6,347
    Resets with a flash and is constantly adjusting it. Log it to confirm.
    Post a log and tune if you want help

    VCM Suite V3+ GETTING STARTED THREADS / HOW TO's

    Tuner by night
    CPX Tuning
    2005 Corvette, M6
    ECS 1500 Supercharger
    AlkyControl Meth, Monster LT1-S Twin, NT05R's
    ID1000's, 220/240, .598/.598, 118 from Cam Motion

    2007 Escalade, A6
    Stock

  11. #11
    Senior Tuner 10_SS's Avatar
    Join Date
    Mar 2012
    Location
    Detroit, MI
    Posts
    1,320
    Quote Originally Posted by ericwilloughby View Post
    Went from 87 octane to E85. How do I reset my knock learn? It seems to be taking weeks to do it automatically
    if it's taking weeks then it's actually adjusting to your current knock levels since your running 87 octane. Why you running that bad gas? Run 92-93 octane, if your lucky then your knock learn will come down to 0.00 or close too it fairly quickly. Also, if you run E85 knock learn will probably go back down to 0.00 pretty quick since it should reduce knock substantially.

    The confusion Knock Learn causes is when you want to maybe tune the timing to eliminate knock, you get knock the Learn Factor incrementing, then because of this knock kinda stops, then as knock stops, the learn factor comes down a bit, then you start getting more knock, the cycle continues and it will never come back to 0.00. This is simply because you have knock and it's doing it's job to reduce it. Your knock log histogram will not be very useful because the Knock Learn will be adding and removing timing, making knock appear then disappear.

    To tune it out, I've come to the conclusion that you need to make high and low octane tables the same... run good 92-93 octane gas, this way you still get a Knock learn value that increments to show you have higher levels of knock, then log where knock is occurring since it should be more consistent. Adjust timing accordingly hopefully the knock stops with 1-2 deg of timing pulled from those areas. Once knock is eliminated then put your low octane table back like it was.

    When you switch to E85 you can add spark in the E85 tables.

    I was logging for awhile and just started pulling a degree or two of timing from my knock areas.. but then I installed headers with no cats and all of my knock went away. So now I will put my timing back and maybe increase a bit in the lower load areas.

    Once done will put my low octane table back to stock, but right now Im usually at 0.00 so that's good.
    Last edited by 10_SS; 05-11-2018 at 02:00 PM.
    2010 Camaro LS3 (E38 ECU - Spark only). MS3X running complete RTT fuel control (wideband).
    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

  12. #12
    I don't have E85 tables. I don't have a alcohol content sensor. Wish I did.
    As I said I switched back to E85 a couple of tanks ago. Taking to long to relearn.

    HOW do I reset klf

  13. #13
    Looks like flashing the modified low octane table reset the klf. Thanks anyway. 1st I've heard of klf. Was it also on the Gen 3 ecm? I thought timing just switched between the 2 tables not a mixture

  14. #14
    Senior Tuner 10_SS's Avatar
    Join Date
    Mar 2012
    Location
    Detroit, MI
    Posts
    1,320
    Quote Originally Posted by ericwilloughby View Post
    Looks like flashing the modified low octane table reset the klf. Thanks anyway. 1st I've heard of klf. Was it also on the Gen 3 ecm? I thought timing just switched between the 2 tables not a mixture
    schpenxel mentioned flashing resets it in earlier post. Not because you put the Low Octane table back to stock. It's a mix, 0.00 = 100% HIGH, 1.00 = 100% LOW.

    If you have High/Low tables you have Knock Learn. If you have anything that sounds like Knock Learn tables, you have parameters to adjust the sensitivity.

    There's a few ways to reset the PCM use whatever method you want.
    Last edited by 10_SS; 05-11-2018 at 11:11 PM.
    2010 Camaro LS3 (E38 ECU - Spark only). MS3X running complete RTT fuel control (wideband).
    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