OVRKILL
Well-Known Member
As I understand it, it's not entirely critical as long as it's in the right context.I'm glad somebody finally asked this question. I've been searching and could only find Subaru guys talk about knock sensors and the octane adjust ratio. Wish somebody could explain how to interpret the different knock sensors. I've read conflicting opinions on the subject whether or not one instance of knock is to be expected or blah blah. If somebody could chime in that'd be cool.
The sensors are very, well, sensitive, and any blip whether it's LSPI, a tiny knock, or full-on detonation, will all come up the same on that counter.
Under throttle, the ECU will gradually advance timing as RPM increases. If there's a little bit of knock from too much timing, the engine will see that count and pull some out. The knock should stop there. On a well set-up car there will be only one count or two at most. If your car keeps knocking, for more than three counts or so, or goes into negative timing at the same time, you have a real problem.
here's a graph of a minor knock event from a pull I made yesterday:
http://i.imgur.com/WHDUmZw.png
If the knock had been more severe, the knock count would continue to increment and the ign correction would pull almost all the way out. This wouldn't matter with preignition, which is why LSPI is so deadly.
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