MerCruiser 305 CID (5.0L), Руководство по обслуживанию

Страница: 705 / 895

DIAGNOSTICS SERVICE MANUAL NUMBER 24
Page 5G-78 90-861327--1 OCTOBER 1999
Code 43 (1 of 3): Knock Sensor (KS) Circuit
FUSE 15A
TO SYSTEM
RELAY
KNOCK SENSOR
MODULE
KNOCK
SENSOR
485 GRN
486 PUR
496 DK BLU
ECM
MEFI 1
MEFI 2
J1-1
MEFI 3
J1-30
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 there are abnormal mechanical engine noises (rattles or knocks), they may give
a false DTC 43. If fuel octane is too low, a false DTC 43 may be set.
Index