BOSCH Hall Effect Electronic Ignition System: Operation

The Hall sending unit (pick-up coil) is mounted inside the distributor on a switch plate. A trigger wheel (segmented shutter) attached to the distributor shaft under the rotor, passes in and out of the air gap of the Hall sending unit.

At speeds greater than 940 RPM, the Hall sending unit signals the ignition control unit to make and break the primary circuit current flow in the ignition coil. There is one trigger wheel shutter or tooth for each cylinder of the engine. Shutter width determines dwell, which is not adjustable.

As the ignition control unit breaks the primary circuit through the coil, secondary voltage is released through high tension wiring, distributor cap and rotor to spark plugs. See Figure.

If engine speed drops below 940 RPM, the idle stabilizer takes over the duty of producing the signal to the ignition control unit, instead of the Hall sending unit. Mounted between the distributor and the ignition control unit, the idle stabilizer senses engine speed earlier, causing ignition timing to advance. Advancing ignition timing causes idle speed to increase, and the Hall sending unit to resume its normal operation.