No knock, knock

Roger Heflin rah at horizon.hit.net
Fri Oct 23 13:23:03 GMT 1998



On Fri, 23 Oct 1998, Roger Heflin wrote:

> 
> 
> 
> Well, I have heard that less fuel will detonate easier, so if it had
> enough less fuel it sounds like maybe, even on exactly the same engine
> it could trigger knock, with less timing.  Just what I have heard.  
> 
> 				Roger
> 

To reply to my reply, the module in the memcal that does the knock
detection is I believe a simple filter of some type.  Filters are very
difficult to build the same, so there could be quite a bit of variance
between them.  They are rather sensitive to component values, and it
is really keep things consistant.   I have built one before and even
using components that were +-5% we got a filter that was closer to
-12% so there could be quite a bit of variance on the knock modules.
That is the frequency that they are looking for could be different
(only slightly, but enough) so that the actual frequency that they
really want is going to be attenuated somewhat more, so requiring the
knock to be louder to trigger the knock signal.

One of these date we need to do some research on what the pinnouts of
the knock modules are and someone needs to design a replacement that
does a better job, and is more consistant.

				Roger




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