Engine Knock - Actron CP9087 Service Manual

Section 2
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What is It?
How it is
Location
When to Test
What to
Inspect
2-26
Testing Sensors
The knock sensor is a piece of piezoelectric
material mounted in a metal housing. The sensor
acts like a microphone - it changes vibrations into a
small AC voltage signal. The sensor usually has a
one wire or two wire connector.
The computer (or other spark timing controller) is
designed to recognize sensor signals caused by
used?
engine knock vibrations. Then, spark timing is
retarded to eliminate the damaging knock condition
Usually threaded into (or bolted on) the engine
block, intake manifold or exhaust manifold. Often
near the cylinder heads.
• Related trouble codes sent by computer.
• Knocking during cruise or hard acceleration (not
enough spark retard), hesitation, poor perfor-
mance and fuel economy (excess spark retard).
Sensor operation (see test on page 2-27). Poor
connections at sensor or computer. Faulty sensor
wiring (open or short circuits). Spark timing. Bad
fuel quality.
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