Knock Sensor Tidbit

[Ludis Langens <ludis@cruzers.com>]

While poking at an ECM chasing signal paths around, I found an
interesting input/output pin.  In the 1227730/1227749 ECMs, harness pin
B8 might be the filtered knock sensor signal.  It connects via a 10K
resistor to the input of a (digital) inverter.  The inverter input is
directly connected to one of the MEMCAL pins which connects to the
hybrid knock sensor filter module.  The inverter input is also pulled to
ground through a 470K resistor, and clipped to 5V via a diode.

It appears that if a MEMCAL contains no knock filter, pin B8 could be
used to input a signal from an external knock filter.  If the MEMCAL
does contain the hybrid module, pin B8 would be an output.

If used as an output, it would need to feed a circuit with a high
impedance input (because of the 10K resistor).  Someone with a knock
sensor equipped 730/749 vehicle should hook a buffer and light to pin
B8.  It would be interesting to hear when/if the light turns on.

-- 
Ludis Langens                               ludis (at) cruzers (dot) com
Mac, Fiero, & engine controller goodies:  http://www.cruzers.com/~ludis/

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