Knock light, was Saab APC fitted to Audi?

[Jim Green]

--- Jesse Clendenning <AWDAudi at Excite.com> wrote:
> 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.

Well, I'll be damned, looks like I have some more wire
splicing to test out.  It would be great if I could
just run the LED off the same knock sensor the ign.
ecu uses.  I'll post what I find out.

Later,

=====
Jim Green
'89 90tq EFI
http://www.geocities.com/jeg1976/car_home.html

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