Ignition System: Description and Operation

This system provides electronically controlled spark advance and eliminates the need for mechanical and vacuum advance controls in the distributor. The Single Module Engine Controller (SMEC) uses many sensors to monitor the engines conditions so that it can fire the spark plugs at the proper time.
The SMEC controls spark advance and ignition coil dwell.


SENSORS
This system incorporates the following devices:
1. The Hall Effect Pickup, used on 4-153 engine, is located in the distributor assembly. The pickup supplies engine RPM and ignition timing data to the SMEC to advance or retard ignition spark.
2. The coolant temperature sensor, located in the thermostat housing, monitors coolant temperature. This sensor provides data on engine operating temperature to the SMEC.
3. The manifold absolute pressure sensor, located underhood on the dash panel and is connected to a vacuum nipple on 4-153 engine or air intake plenum on V6-181 engine, monitors manifold vacuum.
4. The optical distributor, used on V6-181 engine, transmits engine speed and crankshaft position signals to the SMEC. The distributor also delivers firing pulses from the coil to each individual cylinder through a cap and rotor.