Laser AWD L4-1997cc 2.0L DOHC Turbo (1992)
Detonation (Knock) Sensor: Description and Operation
Detonation (Knock) Sensor Circuit
PURPOSE
The knock sensor converts knocking vibrations into electric signals. The signals are used by the ECU to control ignition timing and turbo boost
pressure.
LOCATION
It is installed on the engine block on the engine block under the intake manifold.
Knock Sensor
CONSTRUCTION
The sensor is a piezo-electric crystal made of three elements: Titanium Oxide, Zirconium Oxide and Lead.
KNOCK CONTROL SYSTEM
KNOCK SENSOR
When engine knocking occurs, the crystal shakes and produces an A/C voltage signal. When engine knocking is detected by the ECU, it retards the
timing (maximum of 12° at the crankshaft) and reduces boost pressure (via the wastegate solenoid) to reduce the incidence. Some reduction in
engine power will be noticed with the reduction in timing and boost.
WASTEGATE SOLENOID
Normally the wastegate solenoid is fully grounded when the key is on, allowing maximum boost by bleeding of wastegate operating pressure.
However if the sensor is shorted (0 Volts) or the circuit is open (5 Volts), the ECU retards the timing and lowers the maximum boost from 12 PSI
to 9 PSI, dependent upon the load and RPM information. When this happens it controls the wastegate solenoid operation to eliminate knocking
three ways:
1. The ECU can disconnect the ground (14 Volts) from the solenoid circuit, causing the solenoid to open and allow manifold pressure to open the
wastegate, thus lowering the boost.