Knock Detection

Knock Detection

The Knock Detection function is used to determine whether the knock sensors in a vehicle are functioning correctly. Traditionally, to determine if the sensors were functioning, the tuner was required to advance the ignition timing in order to cause knock, and oftentimes the tuner may forget to retard the timing back afterwards. The knock detection function incorporated into Haltech ECUs and ESP allow the user to temporarily advance the timing for a set time limit, as chosen in the setup menu. After the time is up, the ignition timing will retard back to the original value. This reduces the risk of long term damage caused by long-term engine knock.

Page Contents

Wiring Tab

Options

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, an output must be assigned in the Connections section, and a light must be wired to this output. It will flash when knock has been detected.

Connections

Shows how the Knock Detection system should be wired. Take note that the Knock Sensor 1 and Knock Sensor 2 wires are shielded, and care should be taken to ensure the shielded does not contact the inner signal wire when making connections.

Light Output

Select an appropriate output wire that you wish to use and it will be assigned to this function. In this case the user is selecting DPO4.

Active State

Determines if the output is normally off and turns on when activated (Low), or normally on and off when activated (high).

Knock Detection Tab

The Knock Detection tab contains a Spectrogram. The spectrogram is used to visualise the intensity of the knock signal over a broad frequency range, allowing the tuner to select the frequency to use for Knock Detection. The best frequency to use is a frequency where there is little or no signal when the engine is not knocking, and while knock is occurring, the intensity at that frequency is obvious and quite strong. This will make it much easier to detect true knock. Right clicking on the desired area of the spectrogram will prompt the user with Set As Centre Frequency selection.

Detection

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 most communications resources are directed to this function and other ESP software functions may appear to 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

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.

Duration

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

Duration

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

Related Tables

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 this table correctly the engine should be tuned so that it is certain there is no engine knock present. Knock Level should be monitored and the table set up so that it is slightly above the Knock Level under all RPM and Load conditions, typically by approximately 3 to 5 dB. When engine knock occurs you should see Knock Level spike to a much higher value which exceeds the values in the table, and then the Knock Detection system will accept this as being a knock event. Up to 3D mapping is available with this table.

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