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 (except Escort and Lynx) have an adapter between the distributor housing and cap. See Figure. Caps are larger than for conventional distributors and have male terminals. Distributors have centrifugal and vacuum advance.

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 4-cylinder and 6-cylinder models rotate clockwise, those of V8 models, counterclockwise.

Distributors for the Escort and Lynx models differ from other models in that they are tang-driven directly by the front end of the camshaft. They have no adapter, and centrifugal advance mechanisms are above the armature and stator assemblies. See Figure. A large, circular rotor provides a dielectric shield over the centrifugal advance mechanism.