MoTeC Knock OKM - Manual (Page 15)

MoTeC Configuration 15
Example 2
The Mitsubishi Evolution Lancer series has a narrowband knock sensor
that transmits a signal different to wideband knock sensors.
The voltage amplitude is high compared to signals from wideband sensors
for the same level of engine noise, so overall energy levels will be high.
The next spectrogram shows a signal from a narrowband knock sensor. It
shows severe detonation at the 2 seconds mark (yellow energy spikes).
The background noise and detonation is concentrated on one frequency,
in this case13 kHz.
Mitsubishi Evolution Lancer: knock frequency analysis
With an example setting of 13 kHz, the log file from the ECU might show
background noise level at 50%- 70% and mild knock showing peaks of
90%. This makes it difficult to detect severe detonation, so an SKM/OKM
centre frequency setting of 13 kHz would be inappropriate.
The detonation energy is high enough to reflect through other frequencies.
For example at 7 kHz, there is less background noise and still relatively
high detonation intensity.
With a setting of 7KHZ the log file from the ECU might show background
noise level at 30-40% and mild knock at 60%. With this setting larger
detonation events can be measured with appropriate action taken as a
result. This would therefore be a better choice for the correct setting.