Knock Control User's Guide

Knock Control User's Guide


What is the Elite Knock Control function and how do you use it.  Knock Detection and Knock Control are only available on the Nexus VCU and Elite 1000 and higher models.

Hey, guess what? We've got a great article here to read and a video. Are you ready to learn something? Let's go!

VIDEO - Knock Control. What it is and why you need it.

What is Engine Knock ?

A 2-stroke piston showing the peppering that is common with engine knock.
Engine knock goes under a number of different names,  pinging, detonation, etc.. and is quite literally uncontrolled explosions in your engine rather than a controlled and timed combustion event.  Engine knock rapidly leads to broken engine components and typically manifests itself as peppered piston tops, followed by cracked pistons and heavily worn bearings.  What you are basically hearing when an engine is knocking is the block ringing like a bell.   Knock in most cases is started by a hot spot causing the air fuel mix to spontaneously ignite before the timed spark is introduced. Most of the time this is because of excessive ignition timing, but can be due to a mixture that is too lean, high component temperatures due to poor cooling, or poor engine design.  The easiest way to cool the engine internals is to retard ignition timing, which diverts energy into the exhaust more than the internal components. 

What is Knock Detection?

Knock Detection involves using a peizo-electric (mechanical to electric) sensor to monitor the frequency at which the engine block is vibrating, and determining whether or not the engine is actually knocking.  For the Elite ECU we use a simple sensor that acts very much like a microphone, sending all frequencies through to the ECU to be processed.   From within the ESP software the correct frequency to be used is then selected by the tuner, with all other frequencies being ignored.   To do this the Knock Detection function must be enabled, and a sensor must be connected to the appropriate ECU input.

There are two main types of knock sensors used in the industry: resonant and non-resonant.

A typical resonant type knock sensor
Resonant Knock Sensors

This type of sensor is typically designed for the exact application and uses a small strip of metal that is designed to have the same resonant frequency as the engine block.  These types simply output a signal as the metal strip vibrates.  They can usually be identified as a screw-in style body with the connector sticking out away from the block and commonly a single wire connection.  Some of these types of sensors can be used with the Elite ECU however the frequency selection will not work as they output a signal across off frequencies to the spectrogram. When running the spectrogram the tuner will notice vertical lines as knock is experienced so frequency selection is not important and can be set to just about anything.   The resonant style sensor is also prone to false-tripping because we cannot tailor the exact frequency to suit the application.

The Haltech HT-011100 Knock Sensor
Non-Resonant Knock Sensors

This type of sensor is more universal and by design will pick up a large range of frequencies making them more suitable to performance applications where we want to pick the frequency to be monitored.  The Haltech Knock Sensor is a non-resonant type sensor.  They can usually be identified by the through-bolt design and commonly have a 2-pin connection with the connector on the side of the sensor.

There is one dedicated knock input (pin A21) on the Elite 1000 and 1500 models, and two dedicated knock inputs (pins A21 and A22) on the Elite 2000 and 2500 models.   The knock sensor should connect to one of these pins, with the other pin of the knock sensor being wired to Signal Ground.

Take note that NGK stress the fact that their sensors should be torqued to the correct specs.  Quote:"The knock sensors have a specific torque. The torque change can affect the signal generated by the sensor. NTK recommends torque of 2.0 to 2.5 kgf.m and does not recommend the use of grease or washers on mounting the knock sensor."

Knock Detection Settings and Tables

Found in Main Setup / Functions / Knock Detection / Knock Detection section

Detection - Start SpectrogramTurns On or Off the Knock Detection Spectrogram which is used to find the knock frequency. The spectrogram will run for 20 seconds and then turn off by itself.Turn on as required.
Detection - Knock FrequencyThe knock frequency can be manually entered here.Found through testing. Changes with each engine.
Detection - Start Angle (BTDC)The crank angle position at which the ECU will start to look for knock.Found through testing but start with -10 degrees.
Detection - DurationThe crank angle amount over which the ECU will look for knock. With a default duration of 40 degrees, and default Start Angle of -10, the ECU will look for knock between -10 and 30 degrees BTDC.Found through testing but start with a wide 60 degrees before narrowing it down afterwards.
Momentary Knock - Ign AdvThe amount of extra ignition timing to be added during the Momentary Knock process.Use enough timing to actually make the engine knock. Start with 10 degrees but more may be required.
Momentary Knock - DurationThe length of time over which the Momentary Knock process will run.use enough time to actually make the engine knock. Typically set to 10 seconds and if there is excessive knock the tuner should reduce engine load.
Momentary Knock - KnockStarts the Momentary Knock processUse as required

Knock ThresholdThe amount of knock signal level over which the engine is considered to be knocking.Typically set to around 3 to 5 db above the normal background noise of the engine when it is definitely not knocking.

Knock Detection Process

There are a number of different methods that tuners will use but the following process is one that I follow when setting up Knock Detection.   There are two main parts to the setup, the knock frequency selection and the knock threshold table setup.    What must be considered is that for the knock detection to work you must identify engine knock. In other words, you do have to make the engine knock so that you know what engine knock looks like for the ECU to be able to do something about it.

There will be times when the knock detection process simply will not work, such as when fuel that has a high enough octane rating that it is not possible to make the engine knock.

To complete the knock detection process the engine must already have a decent level of tune completed. The fueling should be where the tuner wants, and a safe level of ignition timing should be entered that is reasonably ball-park.

Knock Frequency Selection

This part involves finding the best frequency for the ECU to monitor when detecting knock. This process only needs to be completed once, and yes you WILL need a dyno to do this process with any form of repeatability.

  1. Set the Ignition Base table to values that you feel will be relatively safe.
  2. Use the Ignition Overall Trim to take out another extra few degrees.  Say -3.0 degrees top give us an extra bit of headroom.
  3. Warm the engine up to full operating temperatures.  Your engine will not want to knock when everything is stone cold. 
  4. Bring the engine up to around 1500rpm.  This rpm is chosen so that there is enough oil pressure to prevent bearing damage during the testing procedure, the piston speed is not high enough to cause damage, and general engine/exhaust noise is low enough for knock to be audibly heard if required.
  5. Start the Spectrogram.  Remember you only have around 20 seconds with each pass so move swiftly.
  6. Load the engine up, typically to half throttle or so.  At the moment with the reduced ignition timing, you should see general background noise only at this point.
  7. Hit the Momentary Knock button and then look for any changes in the spectrogram pattern.  Even a mildly trained ear should hear any knocking and correspondingly should see brighter spots appearing on the spectrogram.  
  8. If no change is heard or seen, increase the Momentary Knock Ign Adv value by 5 and repeat until you do see a difference.  Sometimes very large amounts of timing are required to make the engine knock.
  9. If knock is too excessive you should ease off the throttle to control how much knock is experienced.  You do not need to destroy the engine to complete this task, you only need to make it knock enough to notice which frequency the knock is occurring at.
  10. Moving the mouse pointer over the spectrogram to the bright spots, typically red. This will highlight the frequency with a faint grey line.  Enter the value it displays as the Knock Frequency.
  11. When completed turn Off the Spectrogram and hit OK.  We are now done with the frequency selection.  

Knock Threshold Table Setup

With the correct frequency chosen for the ECU to look at for knock, we now need to tell the system what amount of noise at that frequency is normal background and at what level that actual knock is at a level that we would like to do something about it.  The Knock Threshold Table is where this is done. 

It is recommended to use the Knock Page Layout provided with ESP to do this next process.  If your ESP software does not have this page, go to the top of the screen and select View / Load Page, select the screen resolution that best matches your laptop screen but if unsure go to the res1366x768 folder, then select the file.

Now view the Knock Threshold table which will look similar to this.

  1. To set this table we are simply going to give the engine a power run on the dyno.  
  2. What we are trying to do is to set up the Knock Threshold table so that it is always around 3 to 5 db above the Knock Signal values at all times.This may take a number of power runs to complete.  
  3. When this is done we will start to introduce more ignition timing. When we earlier used the Ignition Overall Trim to take out 3 degrees, now we will start to head back towards zero and even into positive values.  
  4. Look for any instances where the Knock Signal exceeds the Knock Threshold values.  Any time this does occur the Knock Count will increase, and you will see how far it exceeded the threshold by looking at the Knock Level values. At this point, the engine is considered to have knocked.
  5. If backing off the timing shows the knock signal to come back to normal then you have completed the setup.
  6. Ignition timing tuning from here can use the Knock Count and Knock Level channels to show then too much timing has been used.

What is Knock Control ?

Knock Control is pretty much the ECU doing something about knock when it is detected.  This involves retarding the ignition timing when knock is detected.  Pretty much all that needs to be adjusted is the amount of Short Term Retard, with a value high enough to stop the knocking being required. Usually the default 5 degrees is enough to do the job so very little input is required other than to turn it on and make some changes only if the default values are not sufficient. 

Knock Control Settings

ModeSets whether there is more than one bank to be controlled or not.Depend on the number of sensors. Unbanked when there is one sensor.
Short Term RetardThe amount of ignition timing retard to be applied when a knock event has been detected.Usually around 5 degrees is enough to stop the engine from knocking, but more can be used if an engine is more sensitive.
Short Term Decay RateThe rate at which the Short Term Retard is reduced back to the normal amount of ignition timing.Usually start with 0.5 with a lower number holding the retard for longer, and a higher number for a shorter time.
Hysterisis TimeThe amount of time after a knock event has triggered the short term retard before another event can trigger the short term retard again.Set to a relatively short time, around 0.1 to 0.3 seconds.

Knock Control Long Term Trim Settings and Tables

Enable Long Term TrimTurns On or Off the Long Term learning functionalityTypically turned off by default. Currently the Elite ECU range do not reverse learn. i.e. it wont put back any learned values when the knocking has been eliminated.
Long Term RetardThe amount of retard to learn for the given cell for each given knock event.Use a small value, around 0.5 deg. using a smaller value means the system will learn too slowly. Set too high and it will learn too coarse.
Max Long Term RetardThe maximum amount of retard that any one cell can learn.Usually set to around 5 degrees, but if your engine is knock prone then allowing it to learn more can be advantageous.
ResetResets the learned values back to all zero.N/A.
Apply To Base TableApplies the learned values to the Ignition Base table, and sets the table back to all zeroes when a single bank is used, or applies what it can when two banks are used and any differences are kept (not zero).Use as required.

Bank 1 Long Term TrimActive when the Long Term Trim is enabled. The axis channels will be locked to use the same as the Ignition Base, however the values themselves can be adjusted to suit.N/A
Bank 2 Long Term TrimOnly available on the Elite 2000 and 2500 models, and if a second sensor has been connected and a second Bank has been configured.N/A

Knock Detection and Control Channels

Information about the channels available to be viewed in the ESP software.

Knock ThresholdKnkThreshTaken from the Knock Threshold table. The amount of knock signal over which a knock event is considered to have occurred.
Knock Sensor 1 SignalKnk1 SigThe signal from Knock Sensor 1.

Knock Sensor 1 Level

Knk1 LvlThe amount that Knock Signal 1 that has exceeded the threshold.
Knock Sensor 1 CountKnk1 CountThe amount of times the signal has exceeded the threshold on Knock Sensor 1. In other words how many times a knock event has been detected.
Knock Sensor 2 SignalKnk2 SigThe signal from Knock Sensor 2.
Knock Sensor 2 LevelKnk2 LvlThe amount that Knock Signal 2 that has exceeded the threshold.
Knock Sensor 2 CountKnk2 CountThe amount of times the signal has exceeded the threshold on Knock Sensor 2. In other words how many times a knock event has been detected.
Knock Detection Light Output StateKnock LightOutputStateShows the state of the output to the Knock Light if one is enabled.
Knock Control Bank 1 Ignition CorrectionKnock B1 IgnCorrThe current amount of ignition correction being applied by Knock Sensor 1. The Short Term Trim
Knock Control Bank 2 Ignition CorrectionKnock B2 IgnCorThe current amount of ignition correction being applied by Knock Sensor 2. The Short Term Trim
Knock Control Bank 1 Long Term TrimKnockB1 LTTThe current amount of Long Term Trim being used for Bank 1.
Knock Control Bank 2 Long Term TrimKnockB2 LTTThe current amount of Long Term Trim being used for Bank 2.


I can't see anything at all on my Knock Spectrogram.

Check that the sensor is connected.  The sensor itself may not be compatible.  When in doubt the Haltech sensor is inexpensive and has shown to present a wide frequency spectrum to the ECU.

I see the background noise on the spectrogram but I can't make my engine knock.

Great, what are you complaining about then?  This mostly happens with fuel with too high an octane to make the engine knock.   A lower grade fuel may be temporarily required to obtain the correct knock frequency.

The knock threshold table is difficult to set up.  I don't change the timing but it will randomly detect knock.  What should I do?

Usually caused by excessive background noise (poor signal to noise ratio). Knock occurs at more than one frequency, usually in what is called harmonics.  Selecting another frequency that has less background noise would be a good way to remove excess background noise.

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