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Re: GMECM Digest V2 #149




--- GMECM Digest <gmecm-digest-owner@diy-efi.org> 

> From: Barry Tisdale <btisdale@cybersol.com>
> 
> After changing heads to a set of 1996 models and
> installing a longer
> duration Isky cam in my Syclone, I'm getting a
> 'false knock' between 1975 &
> 2075 RPMs.  Accellerating, steady state or coasting,
> all the same.

Does it do it under no load at all? (Ie, in neutral?)

  Goes
> right to max retard (18°) in a very short time. 
> Major fueling changes in
> this area have *no* effect. 
> 
> Obviously, this is of electrical or mechanical
> origin - no wiring changes,
> so must be the sensor 'hearing' something relative
> to the cam or stiffer
> valve springs that its filter circuits interpret as
> knock.
> 
> Anybody heard of this?  My first thought is to
> disable the knock sensor
> below 2100 RPMs ww/ an aftermarket circuit.

Well, you really wouldn't have to use an aftermarket
circuit, you can do it with a few cal data tweaks.
Just set the ESC attack rate to 0 for 2000 RPM and 
under.

That being said, I don't recommend doing this.
Grumpy's
right, you'll need to systematically isolate things 
until you find the source of the problem.

You might want to try something that was mentioned
here
a few weeks ago... hook the knock sensor into the mic
input of a sound card and record the waveform. If you
can determine what frequency the false knock is
happening at, you might be able to isolate the problem
easier. 

HTH,

Dig
turbodig@yahoo.com
'91 Sy - 12.53@105

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