Pre-Ignition
The premature ignition of the air-fuel mixture before the spark plug fires, usually caused by hot spots in the cylinder.
Pre-ignition is an abnormal combustion event in an internal combustion engine where the air-fuel mixture is ignited before the spark plug fires. It is caused by an ignition source independent of the spark, such as a glowing carbon deposit on the cylinder wall, an overheated spark plug tip, or a sharp edge in the combustion chamber that has reached extreme temperatures.
When pre-ignition occurs, the flame front expands while the piston is still moving upward on its compression stroke. This causes a rapid, dangerous spike in cylinder pressure and temperature before the piston reaches Top Dead Center. The piston is forced to fight against this premature pressure, which can cause severe mechanical stress.
Left unchecked, pre-ignition will quickly destroy engine components. It can melt holes in pistons, break piston rings, bend connecting rods, and burn exhaust valves. Resolving pre-ignition requires identifying and fixing hot spots, cleaning carbon buildup from the combustion chamber, ensuring the correct spark plug heat range is used, and verifying proper cooling system operation.