FUEL INJECTION DESCRIPTIONS AND SYSTEM OPERATION
SERVICE MANUAL NUMBER 24
KNOCK SENSOR
On MEFI 1 and MEFI 2, the knock sensor is mounted on the lower right side of the engine
block. MEFI 3 models do not have a knock sensor module mounted on the engine; it is lo-
cated internal to the ECM.
73051
When abnormal engine vibrations (spark knock) are present, the sensor produces a voltage
signal which is sent to the KS Module and then to the ECM. The ECM uses this signal to
aid in calculating ignition timing.
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.
b
c
a
e
d
Knock Sensor System
a - Electronic Control Module (ECM)
b - 12 Volts Battery Positive
c - 8-12 Volts
d - Knock Sensor
e - Knock Sensor Module
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.
CAUTION
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.
Index
Page 5D-18
90-861327 OCTOBER 1999
| Categories | Mercury MerCruiser Manuals |
|---|---|
| Tags | Mercury MerCruiser 305 CID, Mercury MerCruiser 350 CID |
| Model Year | 1998, 1999, 2000, 2001 |
| Download File |
|
| Document File Type | |
| Copyright | Attribution Non-commercial |
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