Spark Control
The flywheel has an extra ring of 100 teeth. As the crankshaft turns, the flywheel sensor receives 2 voltage pulses from each tooth. It therefore can count the teeth or sense each 1.8° of crankshaft rotation.
One of the flywheel teeth, called the reference tooth, has a special soft iron insert. When it rotates past the crankshaft sensor, the sensor sends 2 stronger pulses to the computer control unit.
By counting the number of teeth which pass the flywheel sensor after the reference tooth, the computer control unit can determine both engine speed and crankshaft position (piston position) in relation to TDC.
When the engine is running, the computer control unit receives information from the various engine sensors. Based on this information, it determines the appropriate time to signal the ignition control unit.
The ignition control unit then makes and breaks the primary circuit to the ignition coil, firing the spark plug. As engine speed and crankshaft position are determined by the crankshaft sensor, the only function of the distributor is to distribute the spark to the spark plugs.