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Originally Posted by floatingkiwi
Hijack alert...
On the subject of knock, how can you tell if your car is actually dialling in any anti-knock? (so to speak)
Matt
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Unfortunately there is no easy way to positively check that the system is working. Worth trying, if you can set up a timing light, difficult with the plug on coil SVX arrangement, is to run the engine with a little throttle while observing the spark advance. Tap a block with a hammer, close to a sensor and the timing should retard slightly.
The usual knock sensor incorporates a metal diaphragm which absorbs shock waves from the engine block and exerts pressure against the crystals inside a piezoelectric disc. As a result, this generates a small A/C voltage signal, proportional to the frequency of the knocks. The sensor used in the SVX has a relatively high impedance of around 500,000 ohms.
Therefore in effect, the sensor is a crude crystal microphone. If you want to have some fun, you could hook one up to the input of an amplifier, run the engine and listen for some music!!