G3500B Engines Caterpillar

Detonation is engine knock that occurs after the air/fuel mixture has been ignited by the spark. The excessive mechanical stress and thermal stress can reduce the service life of the engine. There are several possible causes of detonation. Examples are a rich air/fuel mixture, overload, a high compression ratio, and high inlet manifold air temperature.

Combustion of the air/fuel mixture prior to the spark is a premature ignition. This is usually caused by a hot spot in the combustion chamber. Possible sources of premature ignition are an incorrect spark plug, an incorrectly installed spark plug, and deposits in the combustion chamber. Detonation can be the result of premature ignition. The premature ignition has the effect of advanced ignition timing.

Although a sensor may indicate the presence of detonation, the problem could be a premature ignition. An indication of detonation can also be caused by excessive mechanical engine noise.

To avoid detecting vibrations that are not related to detonation, the Electronic Control Module (ECM) only monitors a detonation sensor when the cylinder's piston is between 0 degrees after top center and 30 degrees after top center. Therefore, the “Block Tap” method of testing the detonation sensors does not work for the G3500B Engine.

For information on testing the detonation sensors, refer to the engine's Troubleshooting manual.