Re: knock sensors

["Scott P. Rafe" <srafe@acc.com>]

Great info, now the rest.  The element is indeed a piezo and you will see
transient voltages of minor values.  However what you did NOT see, good
thing since you were no-load, is the output when a "ping" or "knock" occurs.
Since you have all these neat 'scopes and such, do the same as before then
"tap" the engine block with a brass hammer.  Watch the 'scope.

Audi electrical connectors are notorious for needing to be CLEANED and
reseated.  Pull the boot, pull the plastic, look inside for the little metal
fingers, squirt the heck out of them with electrical contact cleaner.  
*Careful as this stuff EATS paint*.  
Next, use either WD40 or electrical grease and LIGHTLY coat the nipples that
the metal contacts are housed in.  I usually give a shot of WD into the
metal fingers as well; one of the most genius A/VW gurus I ever worked with
uses the elec. grease.  

FWIW: all of my Audi and watercooled VWs have a can of WD40 in the glove
box.  Condensation inside the connector boot can be a real problem.  Boots
MUST NOT be torn and MUST be reseated all the way.  Replacements are
available.  So are whole connectors if you crack one.

WARNING:  ANALOG volt/ohmeters use substantial voltage/power throught the
probes depending on the scale selected.  YOU CAN FRY computer-based
electronic equipment with one of these.  A mis-applied voltage from ANY
source (even static in some cases) can ruin your day.  Be careful what you
are playing with.

*Chips do not care nor do they give any warning that they are about to
toast*  Your stereo/VCR/*EXPENSIVE AUDI COMPUTER* will simply not work any
more and no amount of cursing or cajoling will bring it back.



Scott


At 10:49 AM 9/28/96 -0500, you wrote:
>Thanks for the response.  I made some measurements this morning using an 
>oscilloscope and this is what I found.  Upon peeling back the connector 
>hood on the knocks sensor plug,...