Spark Knock is a knocking, rattling or pinging noise.
It could be heard when he engine is accelerating or is working hard under load.
Spark knock means the fuel is detonating.
Detonation is when the fuel explodes erratically instead of burning smoothly.
It occurs when there is too much heat and compression in the combustion chamber. It is similar to pre-ignition, but pre-ignition is when the fuel ignites before the spark occurs. Pre-ignition can burn a hole right through the top of a piston. The knock sensors work by sensing the “knocks” or noises the engine makes when the pressure and heat in the engine is too much. When this happens, the sensor picks up the noise or the vibration being made.
You will find the knock sensors on the intake manifold, the cylinder head or the engine block. Once there are vibrations sensed, the powertrain control module receives a voltage signal and uses it to change the timing of the ignition and stop it from detonating. By doing this, the engine will be protected from being damaged during pre-ignition.
So if the knock sensor fails then this detonation cannot be regulated and will result in huge damage to your engine. That is why it is important to recognize what the symptoms are of a failing knock sensor. The ECM compensates for knock by retarding the ignition timing (causing it to fire later). The knock sensor then listens for knock on subsequent engine rotations and gradually releases the timing retardation until the ignition timing is back at its original mapped setting.
Knock occurs if any of the following are present:
- Very high combustion temperatures
- Over-advanced ignition timing
- Lean air/fuel ratio (causing high temperature)
- Carbon deposits pre-igniting the air/fuel mixture
Usually a bad knock sensor will trigger the “check engine” light to flash on your vehicle’s dashboard. Sometimes, using cheap gasoline causes detonation. Try filling your vehicle with a higher grade of gasoline, and if the light is still flashing.
If the knock sensor is not working properly, you will likely hear sounds emitting from the engine. You may hear loud thumping noises that become louder over time. The noise is a result of fuel and air igniting inside the cylinder, instead of reaching the point of combustion.
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