Mercury MerCruiser MCM 454 Mag MPI Service Manual page 677

GENERAL SYSTEM DIAGNOSTICS
Chart A-7 (1 of 6): Ignition System Check
"+"
IGN
d
m -
CIRCUIT DESCRIPTION:
The Distributor Ignition (Dl) system receives supply voltage from the system relay through
CKT 902 to the ignition coil gray connector "B". Inside the ignition coil, the gray connector
terminal "B" is connected to the black connector terminal "B." Supply voltage is delivered
from the ignition coil black connector terminal "B" to the distributor Ignition Control (IC) mod-
ule "+" terminal through CKT 3.
Inside the distributor, the pick-up coil and pole piece will produce a voltage signal for cylinder
spark. The voltage signals are processed in the IC module and sent to the ECM. The ECM
will decide if the engine is in the cranking or running mode and adjust timing accordingly.
The voltages or signals are sent between the ECM and the IC module through CKT's 423,
430, and 424. CKT 453 is the ground circuit.
The IC module will send the voltage signal to the ignition coil black connector terminal "A"
through CKT 121. The signal will trigger the coil creating secondary spark to be produced.
This secondary spark is sent to the distributor by a high tension lead.
Index
Page 5E-84
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"C"
BLK CONNECTOR
GRY CONNECTOR
a
TACH
b
c
902 RED
3 PNK
121 GRY
121 WHT
GRY CONNECTOR
e
a - Ignition Coil Connector
b - Distributor
c - To System Relay
d - Ignition Coil
e - Distributor
f - Tach Wire
g - Ignition Control Module
h - Pick-up Coil
i - Distributor 4 Terminal Connector
j - Ignition Control (IC)
k - Dist. Reference "high"
l - Bypass
Dist. Reference "low"
h
g
i
f
SERVICE MANUAL NUMBER 23
j
k
l
m
90-861326--1 MARCH 1999