Knock Indicator Theory of Operation Contributed by Larry Fisher (GNone@tiac.net) 3 July 1996 The turbo Buick engine control system retards spark timing when "knocking" is detected so that engine damage can be prevented. The knock indicator described here and shown in related diagrams is a diagnostic tool that informs the driver when such knocking is occurring. Knock Detection Overview ------------------------ The ECM (Electronic Control Module - engine computer) is signaled that knock is occuring by the ESC, or Electronic Spark Control module. The ESC module is a band-pass filter and logic driver circuit that is connected to an acoustic sensor mounted on the engine block. Normally, the output line of the filter going to the ECM is held "high," or about 10-12 volts. When the filter detects knocking-type sounds, it "grounds" the signal line going to the ECM. On '84-'87 Turbo Buicks and the '89 Turbo TA, the sensor is mounted on the rear of the engine block, above the transmission bell housing. On '86-'87 Turbo Buicks the ESC module is mounted on the inner side of the passenger fenderwell in front of the heater fan. The purpose of Knock Indicators ------------------------------- Aftermarket knock indicators are used as tuning tools and warning devices to prevent engine damage. As a tuning tool, a knock indicator is frequently used as feed-back on whether the engine is operating under too much boost. Boost is one easily-adjusted performance variable that is commonly adjusted to fine-tune a car for maximum performance. To be completed: what the knock indicator does how a knock indicator works How this circuit works - characteristics of operation - diagnostic assistance. potential additions and variations (based on the basic sense method)