OMEM710 Hardware Manual 2v11
50
Engines make mechanical noise that varies dependent on engine speed. The Knock Ambient
Noise Table describes this normal background engine noise when running out of knock. The
parameter KNKRAW shows the current noise measured by the knock sensor. Logging the
parameter KNKRAW on a full load engine run whilst using a safe ignition map allows you to draw
the table of normal noise.
When KNKRAW exceeds the Knock Ambient Noise table values, the engine is assumed to be in
knock. The level of noise above the normal noise is shown by the parameter Knock.
When knock is discovered, the ECU needs to react by retarding the ignition to stop knock, and
increase the fuelling to cool the cylinder.
The Knock value causes an ignition retard (Knk Ign Retard) and an increase in fuel (Knk Fuel
Increase) proportional to the Knock level. The ECU will make these changes to the timing and
fuelling every 4ms until knock has stopped. The extra fuel and the ignition retard are capped to a
maximum regardless of the calculated values by Knk Fuel max and Knk Ign Retard max.
After knock has stopped, the fuelling and ignition values need to be returned to normal. The rate is
set by Knk Restore Rate (engine revolutions) and then Knk Fuel Restore (% fuel per rate) and
Knk Ign Restore (degrees ignition timing per rate).
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