The HEI (EST) distributor uses a modified ignition module. The module has seven or eight terminals instead of the four used without EST. Different terminal arrangements are used, depending upon engine application.
To properly control ignition/combustion timing, the ECM (or PCM) needs to know the following information:
The ECM (or PCM as applicable) uses information from the MAP and coolant sensors in addition to rpm to calculate spark advance as follows:
Incorrect operation of the EST system can cause the following:
The EST system consists of the distributor module, ECM or PCM (and its connecting wires).