Knock Sensor: Description and Operation

Knock Sensor:

PURPOSE
The knock control system allows calibration of the ignition timing for normal operating conditions, while eliminating the danger of knock or detonation due to influences by heat, load, fuel quality or engine deposits.

Knock Sensor:

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
The two knock sensors (A16) which are mounted on the engine block are subjected to vibrations generated by knock. The vibrations cause a small distortion on the surface of the piezoelectric crystals, which consequently generates a small voltage. This voltage is read by the HFM-SFI control module. The control module retards the ignition point for an individual cylinder by 3° crankshaft angle per ignition cycle (Max. of 12°). The knock control system develops its maximum ignition retard of 12° crankshaft angle at a coolant temperature of 91° C (194° F).