RE: Testing Knock Sensors

["Dupree, Jim" <dupree@alldata.com>]

This won't always work because some of the systems are cylinder selective
and retard timing based on which cylinder is knocking and only retard the
cylinder that is knocking. If the knocking is not detected in the time frame
the computer recognizes as a specific cylinder it (the computer) will ignore
the knocking as mechanical noise. If you happen to tap at the right time for
cylinder #1 it will retard the timing your are seeing with your light.
Knock sensors are not easy to test, I prefer to test with an oscilloscope or
the replacement method.
Jim Dupree

		-----Original Message-----
		From:	Huw Powell [mailto:audi@mediaone.net]
		Sent:	Thursday, December 02, 1999 12:36 PM
		To:	ozitzmann@atmi.com
		Cc:	quattro@audifans.com
		Subject:	Re: Testing Knock Sensors

		> This method has been mentioned before, although I haven't
used it or
		> advocate it myself.
		> 
		> Take a long bar that can reach the block around cylinder
#1 on the sensor
		> side. Should be made from steel. Tap the free end lightly
with a hammer
		> and see the voltmeter connected to the plug fluctuate. I'm
sorry that I
		> don't have specifics.

		you also should be able to watch the flywheel with a timing
light, as
		your talented assistant taps the block (or the sensor - but
with
		something light like a thin screwdriver - very lightly!),
you will see
		the timing get retarded as the ECU "hears" the knocks you
are making and
		takes corrective measures.

		This of course also tests the whole system all at once, if
something
		isn't working you won't know what it is.

		-- 
		Huw Powell

		http://www.humanspeakers.com/audi/

		82 Audi Coupe; 84 4kq; 85 Coupe GT; 73 F250

		http://people.ne.mediaone.net/audi/thoughts.htm