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 Electronic Control Module (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, off-idle, 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.
ELECTRONIC CONTROL MODULE OPERATION
Each Dura-Spark II module has 6 wires in 2 connectors. The Red and White wires are ignition feed wires. The White wire is for cranking, and the Red wire provides for normal engine operation. The Red wire circuit contains a 1.1-ohm resistance wire. The current to primary circuit of the ignition coil is turned off and on through Green wire.
The Orange and Purple wires transmit signals to ECM from reluctor (armature) and pick-up coil (stator) in distributor. The Black wire is used to ground ECM through distributor housing.
Electronic control modules of the UIM type, having the third connector, provide for additional spark timing control. This connector receives a signal from the Ignition Barometric Switch, Ignition Timing Vacuum Switch, or the MCU module depending on engine calibration.
IGNITION COIL OPERATION
The ignition coil is energized when ignition switch is in the "ON" or "START" position. The coil contains a positive "BATT" terminal, a negative "TACH" terminal, and a secondary terminal.
A special connector attaches Green wire from ECM to negative coil primary terminal ("TACH"). The wire from ignition switch to positive coil primary terminal ("BATT") is located on opposite side of the connector.
Dura-Spark systems are protected against electrical currents produced or used by other vehicle component during normal operation. However, damage to ignition system can occur if proper testing procedures are not followed.
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Wednesday, February 18th, 2009 AT 11:06 PM