HOLDEN GEN III V8, Service Training

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GEN III V8 ENGINE MANAGEMENT
KNOCK SENSORS
Varying octane levels in today's petrol may cause
detonation in some engines. Detonation is caused
by an uncontrolled pressure in the combustion
chamber. This uncontrolled pressure could
produce a flame front opposite to 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. Light detonation
occurs when the point of maximum pressure has
been exceeded. To control spark knock, two knock
sensors are used on the GEN III V8 engine. 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 sensors detect abnormal mechanical
vibration (spark knocking) in the engine. There are
several calibrations of knock sensors because
each engine produces a different frequency of
mechanical noise. The knock sensor is specifically
chosen for this engine to best detect engine knock,
over all the other noises in the engine.
The knock sensor produces an AC output voltage
that increases with the severity of the knock. This
signal voltage inputs to the PCM. This AC signal
voltage to the PCM is processed by a Digital Signal
Noise Enhancement Filter (DSNEF) module. This
DSNEF module is used to determine if the AC
signal coming in is noise or actual detonation. This
DSNEF module is part of the PCM and cannot be
replaced.
The processed knock sensor signal is then supplied to the PCM. The PCM then adjusts the ignition control
system to reduce the spark advance. How much. the timing is retarded is based upon the amount of time knock
is detected. After the detonation stops, the timing will gradually return to its calibrated value of spark advance.
The Knock Sensor system will only retard timing after the following conditions are met:
• The engine run time is greater than 20 seconds. • The engine coolant temperature is greater than 70°C.
• The engine speed is greater 1650 RPM. • The manifold absolute pressure is less than 60 kPa.
DTC P0325 indicates an internal PCM malfunction related to the knock sensor system. DTCs P0327 and P0332
indicate that a knock sensor or knock sensor circuit is malfunctioning.
GEN III V8 ENGINE MANAGEMENT Page • 59