Knock sensor operation (lots of questions)

[hoshy]

Hi guys. How does the ecu deal with this knock sensoer. does it have trim map so the retarding becomes permanent?

Does the car auto advance to make optimum power?

Or does the sensor just operate in a kind of dynamic mode, if if detects knock then it retards for the duration of knocking then returns to program timing?

Also what kind of signal does the sensor put out?

How does the ecu respond, is the cut-back proportional to sensor output or is it a percentage of advance, maybe fixed 5degree for example?

Does it only affect timing or are there other changes, fuelling maybe?

Thanks in advance guys.

Oh, and if anybody knows of a good book on the deep inner working of motronic now would be a good time to mention it

[Turbo-Brown]

This is all paraphrased from the book of words that came with an OMEX ECU I've got, but hope it's of some help

1) Think it retards the ignition by a set amount, and then advances it again to see what happens, when it detects knock, it repeats the process.

When it detects knock, it also gives the offending cylinders (in a banked system like on the M3) an extra squirt of fuel to cool the cylinder.

2) The system does auto advance within set parameters to make optimum power. This is why knock equipped cars can make better use of Optimax etc. than non knock equipped cars.

3) The sensor is essentially just a microphone. The ECU listens to the output from this but is programmed to listen for the characteristic ping of knock.

However, once the engine's running above a certain speed (which doubtless varies from engine to engine) the background noise being generated prevents the ECU from hearing knock.

4) Pretty sure that it's set to cut back by a set amount, like the 5degrees or whatever you tell it, and then advance again. Kinda trial and error I guess.

Hope that's some help mate

Alex

[hoshy]

Thanks Alex, congrats on finishing the TT project

That answers pretty much everything I wanted to know.

Do you (or does anybody else) know if this info is correct specifically for motronic (1.3 and others)?

Just out of interest does anybody know what a knock sensor sine wave looks like when it's detected? Frequency spikes etc? Or is it not that simple?

[hoshy]

Ok, have answered my own question on the sinewave info.

http://home.netcom.com/~bsundahl/knock/ ... Sounds.htm

http://www.picotech.com/auto/waveforms/ ... ensor.html

I love the picotech guys!

[Brianmoooore]

Has this strayed from the engine swaps forum? Don't want to give everbody the impression that E30s have knock sensors.

[hoshy]

err.. m40b18 - Are you saying doesn't have one?

[Jordan]

No e30 that I know of have knock sensors...

[tim_s]

don't think the e30 m40b18 has knock sensors fella. the m42 in the e30 doesn't and that's motronic 1.7.... not even sure if the e36 m40 has them either, the e36 m42 does though.

[hoshy]

well well well... looks like I got egg on me face here then haha. Somebody told me they did and stupidly I didn't check...