Ignition System - DURA-Spark II: Operation: Distributor

A reluctor, containing same number of teeth as engine cylinders, turns with distributor shaft. The pick-up coil contains a permanent magnet, causing a magnetic field around pick-up coil.

As teeth of reluctor approach and pass pick-up coil, the magnetic field builds and collapses. This causes a signal to be sent to the ECM. The ECM turns the ignition coil primary off and on, causing a high voltage surge in the secondary.

Dura-Spark II distributors have both centrifugal and vacuum advance mechanisms. On single diaphragm vacuum units, increased vacuum causes the movable pick-up coil to pivot on lower plate assembly, advancing spark timing.

On dual diaphragm units, outer (primary) diaphragm operates from carburetor vacuum to provide timing advance during normal, idle-off, driving conditions. The inner (secondary) diaphragm operates from intake manifold vacuum and acts to retard ignition timing. The inner diaphragm is connected to outer diaphragm rod by means of sliding linkage. Stronger intake manifold vacuum overrides carburetor vacuum during closed throttle operation to retard timing.