Detected - Mercury MerCruiser MCM 454 Mag MPI Service Manual

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SERVICE MANUAL NUMBER 23

Code 43 (1 of 2): Knock Sensor (KS) Circuit (Scan) - Continuous Knock

Detected

CIRCUIT DESCRIPTION:

Knock Sensor (KS) system circuit is accomplished 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 or engine coolant temperature is above a certain value.

DIAGNOSTIC AIDS

Check for the following conditions:

After repairs, clear DTC's following "Clearing Trouble Codes" procedure at the front of this

section. Failure to do so may result in DTC's 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.

TEST DESCRIPTION:

90-861326--1 MARCH 1999

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Knock Sensor Module

To System Relay

Starboard Knock Sensor

Port Knock Sensor

Knock Sensor Signal

Poor connection at ECM. Inspect harness connectors for backed out terminals,

improper mating, broken locks, improperly formed or damaged terminals, and poor ter-

minal 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.

Step 2. This step determines if ignition voltage is available to power up the KS module.

Step 3. This step checks the ground circuit from the KS module. If the test light is dim,

check ground CKT 486 for excessive resistance.

Step 4. This step checks if a voltage signal from the KS module is present at the ECM.

TROUBLE CODE DIAGNOSTICS - 7.4L MPI

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