Engine Control Module (Ecm) And Delco Est Distributor System - Mercury MerCruiser MCM 454 Mag MPI Service Manual

SERVICE MANUAL NUMBER 23

Engine Control Module (ECM) and Delco EST Distributor System

The Delco EST Distributor operates independent of the ECM. Dwell time and spark advance
are controlled by the ECM. Voltage signals between the two are processed by the Ignition
Control (IC) module inside the distributor.
The ECM uses inputs from various sensors to calculate the ignition spark timing. It also uses
a signal from the IC module to tell it what the engine rpm is. A circuit within the IC module
converts the pickup coil voltage to a square wave engine rpm reference signal. This signal
is called Reference High (REF HI). The ECM needs something to compare the REF HI value
against. This is done by an additional signal called Reference Low (REF LO). These two
signals give the ECM precise engine rpm. Two other lines between the ECM and IC module
are called the bypass and IC circuits. They control the IC operation.
Once the ECM knows if the engine is in the cranking or running mode, the ECM will electroni-
cally control the spark timing accordingly.
Inside the distributor, the pick-up coil and pole piece will produce a voltage signal for cylinder
spark.
Index
90-861326--1 MARCH 1999
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MULTI-PORT FUEL INJECTION DESCRIPTIONS AND SYSTEM OPERATION
Page 5B-25