What is a knock sensor?
A knock sensor is a low voltage producing device (a signal producer) that allows your vehicle to run at the very peak of advanced engine timing without allowing very damaging engine knock caused by cylinder pre-ignition. Today's motors have high output or horsepower and have very low quality gas to run them. The engine knows that the fastest way to increase performance is to automatically advance the timing. The knock sensor lets the ECU know when knocking occurs so it can retard the timing a bit and stay at the maximum RPM's possible without damaging the engine.How does it work?
The knock sensor is located in the engine valve or cylinder at the back of the motor or it can be located in the intake manifold close to the point where it connects to the engine block. Seated in these positions next to the cylinder, the sensor can feel the vibration of engine knocking caused by costly pre-ignition. Feeling the vibration, it emits a small voltage charge that is transmitted back to the ECU. The ECU, now understanding that the engine knock is occurring, retards the timing until the sensor does not feel any further vibrations. Is engine knock really that bad?
Engine knock is definitely bad. The knocking is created by the ignition of fuel and air inside the cylinder before the valve reaches the highest point of the rotation where combustion is supposed to occur. At the minor end of the spectrum, this causes inefficient gas use and rough idle or vibration while driving. On the more severe side, this ignition of fuel can cause very costly wear and burn damage to cylinder heads, the cylinders themselves, gaskets, and pistons. Repairs can easily get into the thousands of dollars.Does the knock sensor do anything else?
Because of its function of only reducing the timing of the ignition at the point there is a knock, the sensor allows your ECU to push your timing to the very edge of it's performance without costly damage to your motor. This translates into more efficient fuel consumption, better horsepower, and longer engine life.How will I know if I have a faulty knock sensor?
We're not being funny here, but you would experience engine knocking and vibration. The knocking can become increasingly loud where you can hear it over your engine noise. If that doesn't happen, you will experience rough acceleration with a jerking sensation like you are hitting a speed limiter. You may also experience misfires, backfires, or smell a strong engine exhaust or burning smell from the pre-ignition happening in the cylinders.