O2 sensor experts plz

Orin Eman orin at cascadia.drizzle.com
Tue Jun 19 13:06:14 EDT 2001

> Correct me if I'm wrong here, the knock sensor is a piezo electric device 
> that, when sensing 5-10khz resonance in the block, will output a voltage.  
> What I want to know is, how much voltage to retard how much timing?  If 
> anyone has any of these specs, I would be very interested.  I am working on a 
> timing retard device based on boost for NA cars.  

The knock sensor is a peizo-electric microphone.  It picks up
everything.  ECUs contain a lot of filtering to pick out
the frequencies associated with knocking.  It isn't as simple 
as retarding so much for so much voltage.  Usually, you end up
with a knock/no knock signal.  On detecting knock, ignition is
retarded a few degrees.  It is gradually advanced back
to the original setting over time.  With a MAC11, the retard
is 2.7 degrees - I consider tripping the knock sensor 'game over'.
My 5k had the running into molasses feeling around 4800 rpm which
was fixed by changing the base timing such that the knock sensor
wasn't 'tripped' (adding more fuel to cool things down would
help too, Scott Mockry has done more research in this area).

In addition, the knock signal is only evaluated over a certain
portion of the ignition cycle - that when knock usually occurs.
This avoids false indications from things like valves closing.

There are a lot of SAE papers on this subject which you should
find and read if you haven't already.


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