Distributors & Ignition Systems - MOTORCRAFT DURA-Spark II Ignition Systems: Operation: Distributor
An armature, containing the same number of teeth as the engine has cylinders, turns with the distributor shaft. A stator (pick-up coil) contains a permanent magnet, causing a magnetic field around the stator's pick-up coil. As the teeth of the armature pass the stator, the magnetic field builds and collapses, causing a signal to be sent to the electronic control module. In turn, the control module turns the ignition coil off and on.
Dura-Spark II systems have an adapter between the distributor housing and cap. See Figure. Caps are larger than for conventional distributors and have male terminals. Distributors have both centrifugal and vacuum advance units.
On single diaphragm vacuum units, increased vacuum causes the movable stator to pivot on lower plate assembly, advancing spark timing. On dual diaphragm vacuum units, the outer (primary) diaphragm operates from carburetor vacuum to provide timing advance during normal off idle driving conditions. It is connected to the stator assembly.
The inner (secondary) diaphragm operates from intake manifold vacuum and acts to retard ignition timing. The inner diaphragm is connected to the outer diaphragm by means of sliding linkage. Stronger intake manifold vacuum can override carburetor vacuum during closed throttle operation, retarding spark timing.
Distributors on 6-cylinder models rotate clockwise, those on V8 models, counterclockwise.