What is a common symptom of detonation in an engine?

A knocking noise from the engine is a classic symptom of detonation, also known as pre-ignition or knock. This knocking occurs because the fuel-air mixture ignites prematurely, leading to a rapid rise in pressure within the combustion chamber. As the flame front travels, it can collide with the incoming mixture, causing a sharp and distinct knocking sound that resembles marbles rattling in a tin can. This noise indicates that the engine is experiencing abnormal combustion conditions, which can lead to engine damage over time if not addressed.

The other symptoms listed might be associated with other engine issues. For example, increased fuel consumption could result from various factors like a rich fuel mixture or malfunctioning sensors, while hesitation during acceleration is often linked to problems with fuel delivery or ignition timing. Excess vibration can be due to mechanical issues unrelated to detonation. Therefore, the knocking noise stands out as a direct and specific indicator of detonation in an engine's operation.