GMECM Digest V2 #149

[Dig]

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

> From: Barry Tisdale <btisdale at 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 at yahoo.com
'91 Sy - 12.53 at 105

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