knock sensor problem

[Steve]

Hi, my knock sensor seems to have stopped working, I suspect the sensor is dead but wondering if anyone knows if there is a way to check continuity between the sensor head and the connector blades?
I've verified that the RCA cable and the wiring down as far as the ECU is fine.
Its a Bosch sensor, part# 0 261 231 006 and looks like this :


The engine is fine for the moment without it, I've upped master fuel so its running quite rich (bangs, pops, burbles, the odd flame) just in case.

[Steve]

found this, off out to test

[[L'e$kro]]

its a microphone so it's a coil, it should have resistance with the ohm meter. Alternatively, you can connect the 2 pins to a minijack cable, then to a stereo or amp, and see if it works..
Nico

[Steve]

yep, tried plugging it into my phone with music playing, no noise on the keypad, not sure if I need something louder.
Have tried checking resistance between pin 2 and ground but am not convinced I'm doing it correctly. Will drop into auto electricians tomorrow.

[[L'e$kro]]

sorry I didn't mean to use the sensor as a speaker Steve. Although it could probably work, it might also damage the sensor.
i meant to use the sensor as a microphone. In my 205 I have a knock sensor hooked up to a Maplin mono amplifier and I detect knocks with headphones, like an electronic stethoscope.
I wired one for a local garage the other day, and if you tap the sensor out of the car with your nail you can clearly hear it in the headphones..

[Steve]

yeah, thats kinda what I meant too, I connected it to the wires on the output side of the sensor when verifying the wiring was ok.
I haven't tried using it as a microphone yet... I'll give that a go later.

Is knock v.clear when using headphones? Does it rise that high above the background noise of the engine ?

[[L'e$kro]]

It's hard to describe. You can hear the valvetrain all the time, and the frequency and volume rises with RPM so it becomes very noisy, but knocking follows a more "analog" pattern that you can hear quite well, that doesn't occur regularly like other noises.
I trained my ear by using sample audio files that I found on a website, i think it may have been the manufacturer of the Phormula K4 who had a bunch of samples in their download section. I'll check if I can find them and edit this message

EDIT: can't find them, sorry.
You might check this instead:


Ideally you want to train on a N/A car as it's harder to break stuff than on your turbocharged MX5! When I started mapping the 205 it was N/A and I had a quite agressive timing map and knocking would occur only in low RPM / high load ie fifth gear at 1k rpm wide open throttle. And I couldn't hear anything when running Ethanol e85. removing 5º would make the noise disappear. You might want to induce knock somewhere safe to train your ear to it..

Nico