MerCruiser 305 CID (5.0L) Service Manual page 708

SERVICE MANUAL NUMBER 24
Code 44 (1 of 3): Knock Sensor (KS) Circuit
KNOCK SENSOR
MODULE
CIRCUIT DESCRIPTION:
MEFI 1 and MEFI 2
Engine detonation or spark knock is sensed with a module that sends a voltage signal to
the ECM. As the knock sensor detects engine knock, the voltage from the KS module to the
ECM drops, and this signals the ECM to start retarding timing. The ECM will retard timing
when knock is detected and rpm and engine coolant temperature are above a certain value.
MEFI 3
Engine detonation or spark knock is detected with a sensor that sends a voltage signal to
the ECM. As the knock sensor detects engine knock, the voltage output level increases and
this signals the ECM to start retarding timing. The ECM will retard timing when knock is
detected and rpm and engine coolant temperature are above a certain value.
NOTE: On MEFI 3 products do not have a knock module. The sensor connects directly to
the ECM.
DIAGNOSTIC AIDS
Check for the following conditions:
•
Poor connection at ECM. Inspect harness connectors for backed out terminals,
improper mating, broken locks, improperly formed or damaged terminals, and poor
terminal to wire connection.
•
Damaged harness. Inspect the wiring harness for damage.
•
If CKT 496 is routed too close to secondary ignition wires, the KS module may see
the interference as a knock signal, resulting in false timing retard.
After repairs, clear DTC following "Clearing Trouble Codes" procedure at the front of this
section. Failure to do so may result in DTC not properly being cleared.
NOTE: if fuel octane is too high, a false DTC 44 may be set
Index
90-861327--1 OCTOBER 1999
FUSE 15A
TO SYSTEM
RELAY
486 PUR
KNOCK
SENSOR
ECM
MEFI 2
485 GRN
J1-1
496 DK BLU
DIAGNOSTICS
MEFI 3
J1-30
Page 5G-81