Ignition System: Operation
The Hall Effect sending unit in the distributor receives voltage from the knock control unit or directly from the electronic ignition control unit. A trigger wheel (shutter blades) mounted on the distributor shaft passes in and out of the air gap of the Hall Effect sending unit, resulting in signal pulses. See Figure. There is one trigger wheel shutter/window for each engine cylinder (5000CS Quattro and 5000CS Turbo have only one window).
On models without timing/knock control units, vacuum and centrifugal advance mechanisms are used. Signals from the distributor Hall sending unit are sent back to the Hall control unit, which opens and closes the primary circuit to the ignition coil, firing the spark plugs.
On models utilizing a knock control unit, vacuum and centrifugal advance mechanisms are not used. The distributor Hall sending unit signal goes directly to the knock control unit which modifies the trigger signal to the ignition coil based on RPM, knock sensor input, vacuum, and Audi 4000S, Audi models with CIS-E III throttle switch inputs.