Page 259 - Foton Workshop Manual - Aumark (BJ1099)

ENGINE CONTROL SYSTEM - KNOCK SENSOR 11-33
KNOCK SENSOR

1. Principle of work
Knock sensor is a vibrated and accelerated speed sensor, installed in the cylinder
block of the engine. The sensitive element of sensor is a piezoelectric element.
The vibration of the engine cylinder block is transmitted to the piezoelectric crystal
through the mass block inside the sensor. Because the piezoelectric crystal is under
the vibration of mass block, it produces voltage in both polefaces, and turned the
vibration signal into the alternating voltage signal outputting. The frequency of the 11
vibration signal caused by engine knocking is much higher than the normal vibration
signal of the engine. Therefore, the knocking and non-knocking signals can be
divided after ECM has disposed the signal of the knock sensor.
2. Function and installation
Knock sensor is used to monitor the knocking of the engine, making judgment on
the operating condition of the engine by outputting the voltage signal to ECU.
Knock sensor is installed on the dummy club between the No.2 and No.3 cylinders
in the intake side of the engine cylinder block.
3. Fault phenomenon and judgment method
(a). Fault phenomenon: poor acceleration, etc..
(b). General causes for faults:
The sensor will be rusted, if it is connected with various liquids such as oil, coolant,
brake fluid, etc. for a long time.
(c). Precautions for maintenance:
• Ensure that the surface of installation dummy club is clean without oily foul.
• In the process of installation, any kind of gaskets is not allowed. And it must be
the metal surface of the sensor that clings closely to the cylinder block.
• High voltage should not be connected between the two pins of the sensor, for it
may damage the piezoelectric element.

Page 259