Can anyone tell me how knock detectors work, and if they can be fitted to an engine that hadn't had them fitted before?

The reason for asking is that I'm trying to develop a map for my Megajolt, but can't hear if the engine's pinking due to the insulating qualities of my helmet, the wind roar and a noisy exhaust!

I don't necessarily want the detector to interact with anything - a light on the dash would be enough.

cheers,
David

Usually 2 piezo microphones stuck on the block, a band pass filter and a level detection circuit in the ECU.

They can be added aftermarket, I had a Knock Link on a STi, you can get some simple LED systems that double as a shift light as well.

Megasquirt has some code for knock detection something like surgeforce or summat, google it.Squirt

[Edited on 31/1/07 by Pants On Fire]

I think they are a Pzio thingy and send a voltage when they sense a knock or ping,
The PCM picks this up and backs of the timing,
Steve,
PS I think I spelt Pzio wrong.

A single light on the dash is not useful, you need a number of lights to show normal operation, a funny noise and det. I've used a knocklink in the past that has exactly that and you'd be surprised how many times the thing flicked up to the middle of the leds on normal road use.

For a cheap solution, get yourself a normal knock sensor, screw it into the block somewhere and connect a set of in ear headphones to the connectors. Stick them in your ears and there you go!

Also check out
http://autospeed.drive.com.au/cms/A_0353/article.html

If it's just for setting things up, use a knock sensor bolted to the engine block. Connect this to the microphone input of, well, anything with a microphone input, and listen to the sound it makes through a set of headphones. You should be able to hear if your engine is knocking or not at lower RPM. At higher RPM, the mechanical noise will probably drown out the knocking unless it is *very* intense.

to do things properly (which DIY knocksense boxes don't....) you'll need to "window" the input signal (i.e. only have the filter electronics listen to it during a small part of the engine cycle) which isn't particularly easy. Just map it using the method described above, stay away from the knock limit and you'll be fine.

edit: damn... to slow ;-)

[Edited on 31/1/07 by sebastiaan]

The technology is easy ie piezo mic, filter, way of controlling ignition if knock occurs.

Difficult bit is filtering the signal. As mentioned, lots of other noise going on, so you need to filter out thousands of not insignificant explosions every minute (not to mentioned valve noise, timing chain etc etc) whilst not ignoring pinking.... The filtering required varies from engine to engine so "universal" aftermarket knock sensor systems don't really exist....

Unless you go to Ion sense technology which isn't dependant upon engine type so much. Basic principle is to apply 400v across the spark plug (between sparks obviously) and measure the current flow (dependant on ions in the cylinder). Shame they're isn't (to my knowledge) an aftermarket ion sense setup

Did a google, and found this VERY useful topic on PistonHeads:

LINKY

I particularly like the el cheapo detector made from plastic tubing and a large tin can, designed by Cosworth! If a proper knock sensor is used with headphones, then the concensus seems to be that the human ear/brain is pretty good at picking the knock out of the general engine noise. There's even a brief WAV file that demonstrates the sound to listen for, which is very useful.

I might have a play to see what I can come up with - anyone know of a suitable donor for a knock detector? One of this type (i.e. with a hole, rather than a screw-in stud) would be ideal. Vauxhalls are mentioned in that topic, but I wouldn't know where to look...



cheers,
David

Apparently a bit of copper pipe hammered flat at one end bolted to the engine with some tube on the other (round) end going a Y-piece on then one bit of tube stuffed in each ear of some ear defenders works quite well.

quote:

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Originally posted by David Jenkins
anyone know of a suitable donor for a knock detector? One of this type (i.e. with a hole, rather than a screw-in stud) would be ideal. Vauxhalls are mentioned in that topic, but I wouldn't know where to look...

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Hmm... when to my favourite scrappy today... several VW's, all carb models! Had a good look round the other cars and a few were injection, but could only see 1 bolt-in type of sensor (and even then I'm not sure it was a knock sensor.)

I wonder how much a new one would cost in GS&F... time to Google, methinks...
(UPDATE - GS&F weren't much use... )

Can anyone else suggest a good source of knock sensors of the type shown earlier?

cheers,
David

[Edited on 1/2/07 by David Jenkins]

Looking at going down a similar route my vems unit has a knock sensor input and you can buy the ones you are after from

Vems Web Shop

but I was put of by the wording. Though not worries as CR at the moment is quite low but future plans may include increasing this .

Regards

Agriv8

quote:

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Originally posted by Agriv8
but I was put of by the wording.

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The one in your picture is a bosch one and the part number is on it

It's a bit hard to read!

[UPDATE: it's 0-261-231-006 - found it elsewhere ]

[Edited on 1/2/07 by David Jenkins]