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Auto Ignition, Knocking, or Pinging

When a gasoline and air mixture auto-ignites and it’s not due to the normal spark event, the combustion wave will collide with the normal spark-initiated combustion wave inside the cylinder, causing the vibration that’s referred to as “knock” or “ping” due to the sound we hear. Depending on the intensity, knocking may be inaudible, barely audible kink-kink-kink or ping-ping-ping, or a violent banging or pounding sound.

If sustained knocking occurs, the pistons will be damaged. Light knocking may occur for quite awhile before major damage occurs, but it will eventually destroy some internal engine components. The chance of knocking is increased by the following characteristics:

• Too much timing advance for the type of fuel being burned.
• Spark plugs with a heat range higher than required by the engine.
• High Engine loads, towing a trailer or another vehicle.
• Burning lower octane gasoline than is required by the engine.
• Increased temperature in the combustion chamber due to poor engine cooling.
• Higher air density occurring without adequate timing/fuel adjustment.
• High inlet air temperatures.
• A lopsided spark plug location in the chamber.
• Excessively rectangular combustion chamber shape.
• Lean air/fuel ratio.

The following tuning adjustments may be performed to reduce or eliminate knock:

• Retard the ignition timing.
• Visually ‘read’ the spark plugs to verify they are the correct heat range.
• Verify that the air/fuel mixture is adequate, too rich or too lean is bad.