90 Quattro 20V (Canada) L5-2309cc 2.3L DOHC (7A) (1989)
Knock Sensor: Description and Operation
Ignition Maps And Knock Sensor Control
Two knock sensors are used to signal the ECU when a sudden severe detonation (knock) occurs in the engine. When a knock is sensed, the ECU
retards the ignition timing, in steps, until the knock ceases. The ECU has two ignition "maps" programmed into its memory. One for premium fuel and
one for lower octane fuels. The premium fuel ignition map is normally the one referenced by the ECU. If knocking cannot be eliminated by retarding the
ignition timing the maximum number of degrees from the mapped point on the premium ignition map (12 degrees), the ECU switches to the other
ignition map. If the knocking stops, the ECU advances the timing, in steps, back to the mapped point for that engine speed and load.