The Electronic Spark Control, also called the Knock Sensor, is an electronic device built by General Motors to help regulate the timing inside of the engine. When combustion inside the engine does not fire properly, a "spark knock" or abnormal vibration can occur. If these vibrations caused by misfires are not reduced, they can cause significant damage to the engine components.
Modern engines are tuned to reduce these knocks as much as possible, however they can still occur under certain conditions. As an engine ages, its timing can degrade, leading to knocks. Outside factors such as the humidity or altitude where the engine is operating can also cause timing issues. Electronic Spark Control compensates for these occurrences.
The vibrations that can potentially damage an engine also help make knocks easy to detect. Because these vibrations resonate at a particular frequency, they can be sensed and located when they occur. Knock sensors inside an engine contain piezoelectric crystals tuned to this frequency, and generate electric signals when the vibration occurs.
While one sensor alone can detect engine knocks, two or more sensors are often used in an engine. Multiple sensors in different locations allow the Electronic Spark Control to locate the source of the knock with greater accuracy.
Once the sensors of the Electronic Spark Control system have detected a vibration, they send an electronic signal to the powertrain control module. This module is essentially a small computer, and can determine the exact location of the engine knock. The control module can then adjust the timing of the engine to compensate and eliminate the vibration.
Often, compensating for an engine knock requires engine timing to be slowed, leading to a temporary reduction in power. Because calculations and adjustments in the Electronic Spark Control system occur so rapidly, however, this drop in engine power is usually unnoticeable.