405 L4-1905cc 1.9L DOHC (1990)
Knock Sensor: Description and Operation
Knock Sensor
PURPOSE
The knock sensor generates a "knock" signal for the ECU. When engine knock is detected, the knock sensor develops a voltage which the ECU
registers. The ECU takes appropriate action by retarding the ignition timing and enriching the air/fuel mixture if necessary.
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 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 ECU which computes it as a reference value.