Mercury MerCruiser MCM 454 Mag MPI Service Manual page 482

SERVICE MANUAL NUMBER 23
KNOCK SENSOR (KS) MODULE (MEFI 1 AND MEFI 2 MODELS ONLY)
When the key switch is turned on, 12 volts are supplied to the KS module B terminal through
the system relay. If this 12 volts are not present, the KS module cannot send the 8-10 volt
signal to the ECM. This will cause a false constant ignition spark timing retard and a Code
will be set.
The KS module monitors the knock sensor's AC voltage signal on terminal E. If no spark
knock is present, an 8-10 volt signal is sent to the ECM by the KS module's terminal C. If
spark knock is present, the module will remove this 8-10 volt signal to the ECM. The ECM
will then retard the ignition spark timing to control the spark knock. If the circuit going to the
module's E terminal opens or shorts to ground, the KS module cannot remove the 8-10 volt
signal to the ECM and no spark retard will occur. The ground circuit for the KS module is
connected to terminal D. If this circuit is open, the module cannot remove the 8-10 volt signal
to the ECM either and spark knock cannot be controlled.
The correct Knock Sensor and KS module for an engine must be used or a spark
knock may not be detected causing sever engine damage.
KNOCK SENSOR CIRCUITRY (MEFI-3 MODELS ONLY)
The MEFI-3 ECM is used with the knock sensor to control spark knock. The KS module cir-
cuitry is within the MEFI-3 ECM. When spark knock is present, a small AC voltage signal
is sent from the knock sensor to the ECM through pin connector J1-30. (If the engine has
a second KS, its voltage signal goes through pin connector J1-14). An AC voltage monitor
inside the ECM will detect the spark knock and start retarding spark timing. A Code will be
set only if the ECM does not see any activity on the KS signal circuit(s).
Index
90-861326--1 MARCH 1999
Downloaded from https://needmanual.com/
a
Knock Sensor System
a - Electronic Control Module (ECM)
b - 12 Volts Battery Positive
c - 8-12 Volts
d - Knock Sensor
e - Knock Sensor Module
MULTI-PORT FUEL INJECTION DESCRIPTIONS AND SYSTEM OPERATION
b
c
d
CAUTION
e
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