I'm making a cheap voltmeter to mount into the dash that'll read the voltage off the knock sensor.
Well that's my question really, does the knock sensor display voltage or pulses? And why does it have 2 wires instead of 1? If it was just a voltage, then it should only need 1 wire for positive.

 

It's a piezo-electric sensor. Basically it's a microphone. One lead is power the other goes to the ECU. It sends pulses of varying intensity. It's more of a spectrum than a digital pulse. One thing DSM guys do is to wire up an LED between the sensor and ECU. This way they can see the knock pulses. The side effects are that the LED may sometimes act as a low power signal filter. In addition there is a minute voltage drop across an LED. However, most of those low amplitude signals would be filtered as noise anyway by the ECU.

 

damn! I was really hoping it was just a voltage that could be read out by a voltmeter.
Tell me something, do you if it's pulses, not a voltage then how can the safc2 report engine knock? On the safc2, it looks like the knock is a voltage readout.

 

I looked at an apexi safc2 wiring diagram and there's only one knock sensor wire to hook it up to. I can build a cheap lcd voltmeter for about $7 and mount it into my dash - but that's if I can get a decent reading out of it. What do you guys think?

I need to know the voltage range of the knock sensor so I can make the voltmeter accordingly.

I really need some advice/feedback here!