Pre-ignition

Ignition of the charge before the spark fires, caused by a hot surface in the chamber.

Pre-ignition is combustion that starts before the plug fires, ignited by a glowing hot spot such as an overheated spark-plug tip, sharp carbon edge, or exhaust valve. Unlike detonation, which happens after the spark, pre-ignition begins early and forces the piston to fight rising pressure well before TDC, generating extreme, runaway cylinder pressures that can destroy a piston in seconds. It is far more dangerous than ordinary knock and often is not cleanly caught by knock sensors, so HP Tuners gives no dedicated readout. You prevent it by tuning conservatively: keep the mixture from going lean (verify with a wideband, never rely on commanded AFR), use adequate-octane fuel and correct heat-range plugs, control intake-air temperature, and avoid stacking aggressive timing with boost. Especially under boost, lean-plus-hot conditions invite pre-ignition, which is why the wideband-before-boost rule is non-negotiable.