What sort of signal is the knock sensor?

[Paul Blackmore]

Hi all,

I've been looking at some ALDL info of VS Holden Commodores taken while 
doing some very hard driving around Winton raceway. (Its hard to type while 
coming out of a corner sidways)

The signal is graphed and appears as a spike varying in height (well value 
actually) from 10 to 255(max).

The signal rarely appears under normal driving conditions but when we were 
pushing the cars hard around the race track at WOT the spikes were coming 
high and often (four or five times while accelerating per gear change).
The signal also usually appears (only once) when blipping the throttle for 
downchange while braking.
It also appears (only once) when the car is stationary and the engine is 
spun up to redline with a WOT.
It appears more so when the engine is warm and less so when the engine is 
cold.

I have been told that the knock sensor would not "go off" that often.
However, could it be that the knock sensor is probably going off more than 
we think but it is just "ignored" by the ECM if it is just a small knock and 
that only big knocks cause the spark to be retarded?

Cheers
Paul Blackmore


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