KSC3 – Using the 0-5v Signal with an Engine ECU
3 min read
KSC Knock Sensor ECU contents view
When the KSC3 detects engine knock it can output a three-level 0-5v signal to an engine ECU. The engine ECU can use this signal to, for example, retard ignition timing, close the DBW throttle, reduce boost, increase fuel and so on, whatever the user chooses.
How the knock signal works
When the KSC3 detects knock, it can output the 0-5v signal for either 0.5 seconds or 3 seconds. This is called the “Indication Duration” and this is chosen by the user to suit their needs.
If the KSC3 detects a knock event again, within the knock Indication Duration, the timer resets. The 0.5/3 seconds is counted from the last knock event the KSC3 detected.
0-5v Signal in Detail
The 0-5v signal has three levels to indicate how far above our volume threshold the detected knock is. Level 1 knock outputs a 0.9v* signal, Level 2 outputs 2.4v*, Level 3 outputs 4.8v*. If no knock is detected no voltage (0v) is outputted.
IMPORTANT: All Levels of knock indication can potentially cause engine damage.
*Voltage are approximate, the Test function in the app should be used to identify the voltage on your installation
Retarding Ignition Timing
Assuming we are using the 0-5v output to retard ignition timing and assuming we are retarding the timing by 1 degree for Level 1 knock, 3 degrees for Level 2 knock and by 6 degrees for Level 3 knock.
If the KSC3 detects Level 1 knock, the engine will pull timing by 1 degree (using the settings in the previous paragraph). Every time the KSC3 detects another knock event within the Indication Duration, the knock threshold will be reduced. This will cause the KSC3 to gradually increment it’s Level output to the ECU until it reaches Level 3 or until the knock stops. This incrementing of knock Level output will be reflected by the LED colour changing (Blue indicates Level 1, Orange Level 2, Red Level 3).
By datalogging the KSC3 0-5v signal on our engine ECU we can see where the KSC3 is detecting engine knock and what happened to stop the knock. For example the knock only stopped when the engine ECU received a Level 3 knock indication from the KSC3.
Reading the Datalog
If we see a single spike of the same duration as our Indication Duration this can mean two things. The knock was a one off occurrence and/or the retard we have programmed into our engine ECU compensation table stopped the knock.
If we see the same spike during the same engine conditions regularly, we might be able to say the ignition map in this area is too advanced. If the spike represents Level 2 knock (and we have Level 2 knock pulling timing by 3 degrees (and Level 1 by 1 degree)) we might be able to say that retarding the timing by 2 or 3 degrees in this area is enough to quell the knock in this area.
Interpreting the Log
Generally, MoviChip can tell you what the KSC3 is doing and why, it is up to the calibrater to interpret when the knock indication is occurring, where it is occurring, what (Level) the indication is and how often it is occurring to determine what the engine wants.
LED Colours
The LED colours can be used to interpret what is happening in real-time.
If we are using the 0-5v output to retard timing, this article has information on what the colour is telling us.
If we are not using the 0-5v output, this article has information on what the LED colour is telling us.
