As humidity increases, air intake volume decreases. This results in lower combustion pressures and temperatures, causing a decrease in the spark plug's temperature and a reduction in available power. The higher the altitude, the lower cylinder pressure becomes. As the cylinder temperature decreases, so does the plug tip temperature. A change to a higher octane fuel, a colder plug, richer fuel mixture, or lower compression may be in order.
Detonation can cause insulators or ground electrodes to break off.
Pre-ignition most often leads to detonation. Detonation is most frequently caused by hot spots in the combustion chamber. As the piston is being forced upward by mechanical action of the connecting rod, the pre-ignited explosion will try to force the piston downward. The resulting shock wave causes an audible pinging sound. This is detonation.