[s-cars] Knock sensor output and stock audi connectors sourse?

Paul Gailus gailus at mindspring.com
Tue Mar 23 00:09:15 EST 2004

The knock sensors are piezoelectric elements that
generate an AC signal voltage from mechanical vibrations.
They are similar to ceramic microphone elements.
The ECU typically needs to do some filtering and
detection signal processing in order to reliably
determine if and when knock is occurring.
There's a lot of background noise from normal
engine operation that makes this task more difficult..

What the ECU knock detection is looking for is
an engine block resonance driven by the sharp
"impulse" from the knock detonation wave.
Some knock detectors (resonant type) have some
of the filtering needed to attenuate the "normal"
engine noise signals already built-in.

While it would probably be fairly easy to build up
some circuitry to detect severe knock from the sensor
output, it would be harder to reliably detect relatively
light knocking.

As far as I can gather, reliable knock detection has
never been easy, and more recent ECUs use more
complex Digital Signal Processing based algorithms
instead of analog signal processing.

With regard to the pinging you've observed, some of
it could be due to just how agressive the software
mods have been. But that's just a guess on my part.


----- Original Message ----- 
From: Trevor Frank <tfrank at symyx.com>
To: <s-car-list at audifans.com>; <audi20v_kruemmer at yahoogroups.com>
Sent: Monday, March 22, 2004 9:13 PM
Subject: [s-cars] Knock sensor output and stock audi connectors sourse?

First, I haven't even looked at this, but

What signal is sent or broken by the knock sensors, I am thinking that
it might just be a 5 volt logic/digital?  Ok so if it is that simple
anyone know what pin?  I need to look at the Bentley to see if it shows
the pin outs.  If it is as simple as a 5 volt digital then it I suspect
it would be easy to also adapt it to a light on the dash or at least to
log it.  If it is some kind of varied analog voltage then I could still
data log it.

Also anyone know of a source for the stock audi connectors, or the pins?

I would really love to log when the knocks are being triggered on a data
acquisition system that I am using.  It would be very cool to put in
connectors between the sensors so that I could make a generic wiring
harness that could just plug in and out, currently I am just cutting
into my stock harness.

Here is another question, why do our cars ping, what is it with the
knock sensors that aren't working as it should?  Or is knock sensing
really worth much at all?

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