Q:

What is the Nissan Altima's knock sensor?

A:

Quick Answer

A knock sensor senses vibrations that occur during engine knock and allows the car's power train control module to reduce ignition timing to prevent knocking. The sensor is located on the engine block, cylinder head or intake manifold and is a piezoelectric material that creates a small charge when vibrated. Engine knock leads to engine damage and is caused primarily by poor fuel, deposits in engine or incorrect spark plugs.

Know More

Full Answer

During normal combustion, the spark plug ignites the fuel mixture and the flame front progresses smoothly from the plug until the fuel mixture is completely burned. During engine knock, however, pockets of spontaneous explosions occur away from the spark plug, producing shock waves that rapidly increase cylinder pressure, causing interference to the engine cycle and catastrophic damage to the pistons and head gasket. Reducing the ignition timing causes the spark plug to fire later, reducing cylinder pressure and preventing knock.

Low-quality and low-octane fuels lead to high cylinder pressure and combustion chamber temperatures, causing fuel to ignite early. Higher-octane fuels burn more slowly and resist detonation due to extreme cylinder conditions. Deposits in the cylinder walls also raise cylinder pressure by taking up space normally used by the fuel mixture. Additionally, incorrect spark plugs may improperly burn the fuel mixture, causing deposits to form in the cylinders and increased operating temperatures.

Learn more about Engine

Related Questions

  • Q:

    Why do diesel engines knock?

    A:

    Most knocks come from the ignition or the injector nailing. Fuel injectors can also cause a knocking noise, especially in older diesel vehicles.

    Full Answer >
    Filed Under:
  • Q:

    Why does my engine knock?

    A:

    Engine knock can be caused by an incorrect air/fuel mixture within one or more cylinders. The knocking sound is the fuel burning unevenly and creating shock waves at the wrong times. The waves can damage the cylinder wall as well as the piston.

    Full Answer >
    Filed Under:
  • Q:

    Where is the oil level sensor located?

    A:

    An automobile's oil level sensor is generally located inside the oil pan. This sensor measures the amount of oil in the pan and sends that measurement to the gauge, alerting the driver when the vehicle needs additional oil.

    Full Answer >
    Filed Under:
  • Q:

    Why does my car make a knocking sound?

    A:

    There are many potential causes for engine knocking noises, and they vary slightly from one vehicle to another. However, there are a few causes of knocking noises that are much more common than others. Some of the usual causes for a knocking sound from a vehicle's engine are low-quality fuel, incorrect spark plugs and deposits forming on the engine's cylinder walls, according to HowStuffWorks.

    Full Answer >
    Filed Under:

Explore