Hello,
I am having some knock issues (see here for details) and need a good way to prove the knock sensor is working. I bought a new knock sensor, hooked it up to an oscilloscope, tapped it, and saw the peaks as I tapped (Note: the peaks seemed in a 0-2V output range, but I didn't tap really hard to not damage the piezoelectric crystal). So I am pretty sure the sensor is good, but I don't think it is working. Here is why:

I connect my ODB II Scanner to phone and turn the car on. I am able to watch the timing advance via this. At idle it runs around 3-16 degrees (averaging around 8). I then take a small wrench and tap on the knock sensor bolt lightly. I see no discernible difference with the timing when I do this.

So my questions:
1) Am I right to assume that tapping the knock sensor should change my timing?
2) Is there a good way to know if my ECU is getting AND using the signal?

Thank you for your time!
-Troy

 

I'm no expert but I don't think one or two taps on a knock sensor is going to activate a timing change through the ECU. I think the sensor is immune to noise and vibration that does not emulate the "rattle" associated with engine knock. Big question is can you hear the knock/rattle when the sensor should be preventing it.

 

Hi Bzeilstr,
Thank you for the response! I agree the sensor could only look for rattle type noise (I.e. only have frequency response in a certain range) so when i tapped with my wrench, I tried my best to imitate that. So I tapped many times at the same frequency I heard the knock when driving. Ultimately, I still hear the knock, but I recently found out through a compression test that my head gasket is blown between cylinders 3 & 4. So I am going to fix that and see if it solves it, which I assume it will.

Thanks
-Troy

 

For those that come acrossed it, my head gasket was blown and that was causing my knock.