Originally posted by sbchevfreak
they work by the piezeo-electric effect(pardon my spelling?) a "ping", or spark knock causes vibration in the coolant which vibrates a chrystal in the sensor causing an induced voltage. the EST circut in the computer anylizes this voltage signal and retards the timing accordingly with a table of set parameters.
Some may work this way, and I am no electronics genious, but not all do. The sensors that I am familiar with are basically just a microphone. For the ECU to work properly with the knock sensor the fequency of generated by the knock has to be known. The gear drive setting it off is an example of a poorly tuned ECU or one that was not designed to work with the gear drive in the engine. I hate to sound like a salesman, but the vems Genboard V3.1 has the ability to "listen" for knock and I am sure that the developers would add the simple hack to enable one of the spare outputs that are now activated by RPM, MAP and a few other modifiers.
Here is a link to instructions on how to make a knock listener that you can use yourself or could add a mic plug and plug into a laptop to record the sounds if you so desired.