Help me identify this!

[thstone]

The knock sensor detects knock or (more correctly) pre-detonation in the cylinders by sensing the harsh vibrations. The ECU will then retard the ignition timing to prevent engine damage. Retarding the timing usually results in a loss of power so the engine can feel weak. The ECU will set the check engine light (CEL) if the sensor or wiring fails.

[njbray]

Thanks for the quick replies and info.
It looks like the wires have been cut really close to the sensor. I am thinking that maybe the knock sensor on the other cylinders is hooked up and this one is deliberately left disconnected. Maybe the motor only needs one.
I have no engine check lights & car runs great.
When I pull the alternator out next week I will look closer.

[njbray]

The battery light went off this morning - runs fine.
Will keep an eye on it.

[njbray]

So it turns out I have a bad alternator - easy.
Just it pulled it out and I can now see what Mr Rat Bastard has been up too. Apart from covering the engine block in poop & peepee he has also eaten through the wires to the knock sensor! See pic. I think I will unbolt the sensor (is it OK to do that?) trim the wires and solder it back together.
I never noticed any effect on performance - maybe I will gain some when done.

Off to order a new recon. Bosch alternator.