Roadmaster Estate Wagon V8-350 5.7L VIN P SFI (1996)
Knock Sensor: Description and Operation
DESCRIPTION
Varying octane levels in todays gasoline can cause detonation in some engines. Detonation is sometimes called spark knock. Detonation is caused
by an uncontrolled explosion (burn) in the combustion chamber. This uncontrolled explosion could produce a flame front opposite that of the
normal flame front produced by the spark plug. The rattling sound normally associated with detonation is the result of two or more opposing
pressures (flame fronts) colliding within the combustion chamber. Though light detonation is sometimes considered normal, heavy detonation
could result in engine damage.
To control spark knock, a Knock Sensor (KS) system is used. This system is designed to retard spark timing up to 20 to reduce spark knock in the
engine. This allows the engine to use maximum spark advance to improve driveability and fuel economy.
The Knock system has the following components:
^
KS module
^
Knock sensor(s)
OPERATION
The knock sensor system is used to detect engine detonation. The PCM will retard the spark timing based on signals from the KS module. The
knock sensor(s) produce an IAC voltage which is sent to the KS module. The amount of IAC voltage produced by the sensors is determined by the
amount of knock. This signal voltage is input to the PCM. The PCM then adjusts the Ignition Control (IC) to reduce spark knocking.
SCAN TOOL DIAGNOSTICS
The scan tool has several positions for diagnosing the KS circuit:
^
KS activity indicates whether or not a knock signal is being detected by the knock sensors. The scan tool will display YES when a knock is
detected.
^
Knock retard indicates the amount of spark the PCM is removing from the IC spark advance in response to the signal from the knock sensors.
^
Spark Indicates the amount of spark advance being commanded by the PCM on the IC circuit.
DTC P0325 indicates that the KS module is malfunctioning or is missing. DTCs P0327 and P0332 indicates that a Knock sensor or Knock sensor
circuit is malfunctioning. If these DTCs are set, Refer to applicable DTC table.
