W/Sealed Module Connector

Fig. 1 Typical sealed module connector distributor:

This system utilizes a distributor similar to the unit used with conventional HEI systems that has been modified to allow spark advance to be controlled by the fuel control system Electronic Control Module (ECM). Modifications to the distributor, Fig. 1, include a revised ignition module and sealed module connector, with additional terminals to receive signals from the ECM, and the elimination of the conventional centrifugal and vacuum advance mechanisms. In addition, some models use a Hall effect switch mounted above the pickup coil in the distributor to provide a reference pulse to the ECM. The ignition coil on HEI/EST systems with a sealed module connector is remotely mounted.
Primary current switching in the HEI/EST system is performed by the ignition module based on reference pulses from the pickup coil as in conventional HEI systems. However, all spark timing changes in the HEI/EST system are performed electronically by the Electronic Control Module (ECM). The ECM monitors information from various engine and vehicle sensors, determines the correct spark timing and signals the distributor to change timing as necessary. An EST bypass circuit is incorporated into the ignition module to allow ignition in case of ECM failure and to allow base timing adjustment.