Knock Sensors (KS) - Monitor The Frequency When Detonation Occurs
Knock Sensors (KS) – Monitor The Frequency When Detonation Occurs

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Engine Spark Knock – That Annoying Knocking, Pinging Or Rattling Sound

Engine Knocking – Pinging – Rattling Noise – Common Causes


So, the knock sensors job is, to monitor the engine for any signs of detonation. Consequently, detonation is the premature ignition, of the air fuel mixture. So, detonation produces, a distinctly mechanical knocking sound. But, is usually detected at higher engine speeds or; a sudden increase in engine load.

So, to improve engine efficiency; the (PCM) keeps the ignition timing, as far advanced as possible. Based on the current operating conditions; such as engine speed, load, throttle position, and vehicle speed. However, any increase in the engine speed load from current conditions; will cause the air fuel mixture to, ignite prematurely.

As a result, producing the same knocking sound, as detonation. So, to prevent detonation; the knock sensor monitors the frequency, at which normal detonation occurs. Consequently, providing the (PCM), with a continuous live data stream; that allows the (PCM), to control the ignition timing.

So, if the knock sensor detects, a change in that frequency; it will generate a new signal voltage. Consequently, that signal voltage is based on the changed frequency. Which the (PCM) then interprets as detonation.

So, to correct this condition, the (PCM) then retards the ignition timing. But, only when the detonation frequency matches a wave amplitude; that is based on, a pre-programmed value.

So, the advantage of this is, that the (PCM), can always keep the ignition timing advanced. Therefore, suitable for any given set of engine operating conditions. As a result, increasing engine efficiency and fuel economy; while reducing emissions. In other words, a defective knock sensor has, a direct bearing on engine operation and efficiency.

Knock Sensors Failure Symptoms:

  • A failed knock sensor will register a trouble code and illuminate the Check Engine lamp (CEL); although some engines will require, multiple failure cycles before storing a code.
  • Engine misfires.
  • Vibration, especially at highway speed.
  • Thumping or knocking noise from the engine.
  • Poor fuel economy and acceleration.

What Causes Engine Knock?

There are multiple reasons a engine knock could occur. Here are a few potential causes:

  • Poor timing: The spark is not igniting, at the correct time.
  • Improper air and fuel mixture: If the ratio of air to fuel is incorrect, this could create ignition problems.
  • Deposits inside the cylinder: Dirt, grime, and contaminants, can enter cylinders and create all sorts of issues.
  • Faulty, unhealthy, or incorrect spark plugs: The wrong type of spark plug, spark plugs with deposit build-up; or incorrect spark plug gaps; could cause poor spark or incorrectly timed spark.

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