Knock Sensor Question

[D Kunnath]

Well,

         Obviously nothing is guaranteed...but I was thinking more on a 
level of how "correct" is this kind of fix knowing that you are kind of 
subverting something that is there to protect your investment...

         My problem seems to be quite a bit different than Craig's...only 
getting one set code (43 EST), and it's intermittent.  Got a scan tool 
hooked up and let someone drive it while I watched the info.  Sure would 
have liked Diacom, but I could see the info.  Sometimes the code will set 
right away from a cold startup.  Most of the time it won't come on until 
after going into closed loop.   I'll be driving along with no SES light and 
when I start from a standstill, there it is like a punch in the face.  SLOW 
acceleration out of nowhere.

         Knock counts on the scan tool after a 20min hot engine drive 
counted no more than 6.  When the driver would accelerate, the knock retard 
was up to 20deg right away...never more that 20, never less.  Different 
starts (more / less pedal) produced the same timing retard.  The other 
values in the scan appeared ok...A/F ratio moving in an expected manner, 
crosscounts by the O2 sensor climbing rapidly, coolant temp, MAP, MAT, TPS 
volts and percent fine...never any other codes set...just this one.

         I even took the "advice" of my GM service manual and went through 
the flowchart for the ESC system to test the knock sensor with an AC 
voltmeter, but I never saw *any* AC voltage from the sensor.  Checked my 
ground to make sure it was ok, and the ground was fine.  I don't exactly 
know if any of this points to the possibility of a bad sensor, but it's the 
only part of the knock sensing system that hasn't been replaced.  Got the 
most recent EPROM release from GM (has knock "module" on the memcal).

         Bruce talked about reading the plugs...this sounds like a good 
idea, but I don't have the experience to know what to look for under this 
type of situation.  How can you "see" which cylinder is under detonation if 
it is at all?  I changed the plugs / wires / cap & rotor all about a week 
ago, and every plug that came out looked the same.  Slightly browned, but 
clean and the insulator and tip were all intact.  No oil residue, no white 
powdery coating...is this telling me anything I should be picking up on?  I 
could just go out and replace the sensor for another $50, but I don't know 
if that is the problem, and I won't learn anything about what is going on 
here.  Anything else to look for in reading?

         DK

At 06:05 AM 6/22/00 -0400, you wrote:


> >          How "safe" is it actually to do this?
>
>Nothing is totally safe.  There are no guarantees, even with things all oem.
>
>   I have a knock sensor
> > problem with my 91 LB9...no audible knock and quality gasoline.  Can't
> > solve the problem.
>
>Are the pllugs showing detonation?
>
>  Replaced the prom, but still get intermittent codes...
>
>What codes?
>
>I
> > wouldn''t mind a fix real soon since every time I hit the gas I get 20 deg
> > retard right away.  Really slows the thing down quite a bit.
>
>Well what are you running?.  Gotta a diacom file?.  What actual diagnostics
>have you done
>Grumpy
> >
> >          DK
> >
> > At 01:42 PM 6/22/00 -0700, you wrote:
> > >Hi Craig,
> > >I had a problem with the sensitivity on my 92LT1. Ended up using a
>straight
> > >+ 45 degree M/F 1/4 pipe fittings to move away from the block. Now it
>works
> > >great. The teflon tape and less torque deal did 0 for me. Just remember
> > >before you do any of this make sure you have no audible detonation and
>the
> > >plugs show no signs of detonation.
> > >                                 Jim
> > >Subject: Knock Sensor Question
> > >Seems I read somewhere you can 'adjust' the sensitivity of the knock
>sensor
> > >by using teflon tape on the threads, or screwing it in tighter or
>looser....
> > >can someone verify this and explain how this works? This is for an '85
> > >L98.....
> > >Thanks!
> > >Craig M.
>
>
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