900 L4-1985cc 2.0L DOHC Turbo EFI (1985)
Knock Sensor: Description and Operation
Knock Sensor
PURPOSE
The knock signal is generated by the knock sensor. When engine knock is detected, the knock sensor develops a voltage which the APC ECU
registers. The ECU then take appropriate action by adjusting boost pressure to reduce knock.
CONSTRUCTION
The knock sensor (C) consists of a housing (3) a piezoelectric crystal (4) mounted on a threaded sleeve (5) between two connector strips (6). One
side of the assembly is fitted with a damping weight (7) and spring washer (8) secured by a nut (9).
OPERATION
Mounted on the engine block, the sensor is subjected to the vibrations generated by knock. The vibrations cause a small distortion on the surface
of the piezoelectric crystal, which consequently generates a small voltage. This voltage is read by the APC ECU.
SIGNAL
The signal from the sensor is a continuous, but variable voltage. The frequency of the voltage is dependent on the amount of engine knock. The
signal is fed into the APC ECU which computes it as a reference value.