Knock Sensor Question

[Bruce Plecan]

>          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...

If everything checks out and the only answer is "false knock" then it's your
only option.  It's not a do this first and ignore what it's trying to say.

>          My problem seems to be quite a bit different than Craig's...only
> getting one set code (43 EST), and it's intermittent.

Might just be the ESC no longer triggers at the self test, in an expected
manner.  ie the self test isn't adding quite enough advance, or the sensor
is going deaf.

 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.

20 knock counts or 20 degrees?.  Just off hand haven't seen a ship with 20d
retard allowed.

 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.

Neither have I.

 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?

Doing tuning really requires a plug magnifier or really good eyes.
Detonation will cause molten macroscopic balls of carbon, or AL to be blown
off the face of the piston.  The "stick" to the plugs porcelian.  They look
like fly turds the're that small
Grumpy

>          DK

> > >          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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