Knock light, was Saab APC fitted to Audi?

[Jesse Clendenning]

I actually meant to post it to the whole list also but forgot to change the
to address.

Yes it does work. I put in half a tank of 87 octane to ensure it did, rather
than the 94 I usually put in it.

The knock sensor works by completing a circuit when knock is detected. Most
knock sensors have 1 or two wires.

1 wire knock sensors are fed voltage and ground to the block through the
sensor when knock is detected. The ECU knows the vehicle knocks when the
voltage travels through that circuit.

2 wire knock sensors are virtually identicle to 1 except the sensor grounds
to the ECU through the second wire. Thus the ECU detects knock once the
voltage reaches that pin.

3 wire knock sensors like on our MC1 are a combination of 1 and 2. Voltage
is supplied on one wire. Internally when knock is detected the current flows
through the second wire to the ECU. Instead of grounding at the ECU, the
current flows through that ciruit and pin on the ECU and travels over the
third wire back to the knock sensor where it is grounded to the block.

I hope this clears things up.
----- Original Message -----
From: "Jim Green" <jeg1976 at yahoo.com>
To: "Jesse Clendenning" <AWDAudi at Excite.com>
Sent: Thursday, June 13, 2002 6:28 PM
Subject: Re: Saab APC fitted to Audi?


>
> --- Jesse Clendenning <AWDAudi at Excite.com> wrote:
> > I did just hook up a knock light to the Mac 11 just
> > the other day. My
> > neighbor has a knock light on his Eclipse and this
> > gave me the idea. I used
> > a similar idea for hooking it up.
> >
> > Basically I used an LED which I put in one of the
> > plastic blocks on my dash.
> > '86 5ktq. The positive lead I hooked up to the 12v
> > signal wire to the ECU
> > from the knock sensor (don't remember color off the
> > top of my head, and no
> > Bentley in front of me). The negative lead I
> > attached to the yellow switched
> > ground wire for the Knock sensor on the ECU. The
> > brown wire for the knock
> > sensor on the ECU just grounds the yellow wire from
> > the knock sensor, as you
> > will notice the yellow and brown wires are connected
> > at the ECU.
> >
> > Whenever the knock sensor completed the circuit
> > internally by detecting
> > knock, my LED will go off and I will know about it.
> >
> > Hope this helps - I will go into more detail if
> > anyone needs it.
> >
>
>
> Have you accually seen it knock yet?  I guess I don't
> know exactly how the sensors work, but I was under the
> impression they didn't just complete a circuit, but
> sent a signal based on the nouise they were hearing
> From there on it should be up to the ECU to decide
> what knock really is.  That's why sensors are so
> specific to the ECU's they go with.  But I could be
> wrong, if it works, it work right?
> Jim
>
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