Knock Detection

Knock Detection

Knock Detection

Allows the ECU to monitor engine knock by enabling up to 2 knock sensors. Knock Detection is the configuration and setup of the detecting portion of the knock system in the ECU. For settings related to Knock Control (such as retard values and long term learning, see 'Knock Control').

The Knock Detection function can be used to test whether the knock sensors in a vehicle are functioning correctly, by temporarily advancing the timing for a set time limit, as chosen in the Knock Detection node, and then retarding the ignition timing back to the original value. 

A spectrogram function is provided to visually confirm the knock sensor readings against audible detection strategies such as 'knock ears'. It can also be used to better find the knock center frequency for the particular application. 


Start Spectrogram

Enables or disables the spectrogram function. When enabled the spectrogram will run for 20 seconds after which it will automatically disable. Whilst running communications resources are directed to this function and other NSP software functions may appear to be slow during this process.

Knock Frequency

Select the frequency at which engine knock is occurring. This should be the frequency where there is the largest difference in signal between no knock and real engine knock. Often referred to as signal to noise ratio. The spectrum analyser below can be used for the identification of this frequency. Look for obvious signal differences when the engine is known to be knocking compared with when it is not. Alternately, right clicking on the spectrogram will give the option to Set As Centre Frequency and obtain this value.

Start Angle (BTDC)

The crank angle position where knock detection will begin to look for knock. Knock typically occurs before the spark event, however the corresponding signal is received by the knock sensor much later. Selecting an advanced angle may cause extra combustion noise to be seen by the knock detection system, and too an excessively retarded value can cause knock to not be detected at all. Experimentation is the best method for finding this value.


The crank angle duration the knock detection system will look for knock. Selecting a narrow duration can improve noise rejection which will give a cleaner signal, but there is also the chance that peak knock signal may occur outside of this crank angle window. Experimentation is the best method for finding this value.

Momentary Knock

In order to confirm that the knock sensors are working, the Momentary Knock function will temporarily advance timing. This is an added safety feature, as the timing will return to the desired timing after a short period of time.

Ign Adv

The angle which ignition timing will be advanced


The period of time that the timing remains at the advanced rate before returning back to normal.

Click the 'Knock' button to activate the Momentary Knock function.


This node can be used to set and configure the various options for the Knock Detection inputs, and Knock Light output.

Knock Sensor 1 - Enable when you are using the Knock Sensor 1 Input.
Knock Sensor 2 - Enable when you are using the Knock Sensor 2 Input. Typically a second sensor is used when a V-engine, or an engine with two bank is being used.
Light Output - Enable when a light is to be used to show when knock has been detected.
Light Output Mode - Determines how the light will operate.
      Use CEL - An already configured Check Engine Light (CEL) will flash when knock is detected. When no knock is present it will perform as a normal CEL.
      Digital – Switched - When selected, a separate light output is enabled and must be wired. It will flash when knock has been detected.

    • Related Articles

    • Knock Control User's Guide

      Introduction 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. ...
    • Knock Control

      How does knock control work ? Knock Control is used to retard the ignition timing in the case that engine knock is detected by the sensors. By enabling short term retard, the knock is reduced, creating a safer system, and protecting the engine from ...
    • What is knock and why you should control it

      This article will provide you with a background knowledge of what ‘knock’ is, how it comes about and what the ECU does to detect and prevent/limit damage occurring if knock does occur.   What is Knock? Knock, pinging, detonation, pre-detonation, ...
    • Knock Threshold

      Knock Threshold The Knock Threshold table is used to allow the system to know when knock has occurred compared to normal background noise. The values in this table are the knock level above which true engine knock is said to be occurring. To set up ...
    • Knock Long Term Trim

      Ignition Tuning - Knock - Long Term Trim Enable Long Term Trim Select this box to enable long term trim of Knock Control Long Term Retard This is the amount of long term retard that will be applied for each knock detection event that occurs in that ...