bhvrdr

After reviewing some posts on timing and knock posts on the web (thank you LA Wolfsburg), I decided to go ahead and purchase some Bosch Manuals. Here is an overview...

The ignition system knock control fucntion (IKC) runs the engine at the knock limit for optimum efficiency, but prevents potentially damaging engine knock (pinking). The combustion process in all cylinders is mointored by means of knock sensors. The structure-borne noise signal detected by the sensors is compared with a reference level that is obtrained for individual cylinders via a low-pass filter from previous combustion strokes. The reference level therefore represents background engine noise when the engine is running free of engine knock. The comparison analyzes how much louder current combustion is than the background level. Above a certain threshold, engine knock is assumed to occur. Both calulation of the reference leval and detection of engine knock can take account of changes in operating conditions. The IKC function generates an ignition timing adjustment for each individual cylinder. This is taken into account when calculating the current ignition angle (ignition retard). When engine knock is detected, that ignition timing adjustment is increased by a specified amount. The ignition timing retard is then reduced in small increments if, over a spedified time period, engine knock does not occur.

-Bosch Automotive Technology

Reading more about the Motronic sytem basically states that as Ross-Tech has stated, using knock voltages to assess whether a car is knocking is not correct practice. It is the timing retard that is dependent on knock voltage...and not static knock voltage either. It is instantaneous changes to the voltage that the computer quickly sees and adjust timing based on. So this is why we can see a car running consistently high knock voltages up to 30v with little to no timing retard. That is because the knock voltage for that car is calculated correctly as normal consistent background noise...perfectly safe. When the computer detects a troublesome voltage change, it will retard the timing in response to the engine knocking. This is why we sometimes see lower knock voltages with high timing retard. The IKC detected the knocking as an instantaneous change in the knock sensor noise and retards timing until the knocking stops.

In conclusion, if you want to monitor how the car is responding to knock activity simply log channel 20, which is timing retard.

cheers! Mike