Question id 13 - Emergency Operations - FAA PPL(A) - Private Pilot Airplane

the spark plugs are fouled or shorted out or the wiring is defective.
hot spots in the combustion chamber ignite the fuel/air mixture in advance of normal ignition
the unburned charge in the cylinders explodes instead of burning normally.

Training tests and timed exam simulations FAA PPL(A) - Private Pilot Airplane