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Old 08-07-2009, 01:33 PM   #1
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Listen to your knock sensor!

This has worked very very well for me so I thought I'd share the wealth. I was having HUGE problems with my knock sensor going insane during datalogs... I brought my final timing down to only 5 degrees at 2500-3000rpm and .5 load, and it still showed 8 degrees of knock retard... So basically, it wasnt knock lol

You may have heard about those expensive knock monitoring thingys "The Knock Box" or "phormula" among others... with the fancy noise canceling headphones, etc... well quite frankly... I dont have $150-300 to blow on this...

There are the other options that give you a light show when they think they hear knock, for around $50-100. But on a noisy engine like mine, who's to say they would be any different from the stock sensor in a datalog? They seemed like a possible waste of money to me.

After replacing my sensor and realizing it is just a microphone, I decided to search around to see what people have done to listen to it. And as it turns out, its really easy to do. Fancy boxes need not apply.

All you need is a 0.1uF (uF = microfarad) capacitor, a 1/8" stereo plug or jack (male or female, you have to find out what you need for your HU), some wire, a ring or spade terminal, and a headunit with aux-in.

1. Solder a length of the "some wire" to the tip and ring wires of the stereo plug. Solder the other side to one lead of the cap.
2. Crimp/Solder a second length of the "some wire" to the terminal. Solder the other side of this to the sleeve (ground shield) wire on your 1/8 plug.
3. Go in your car and remove the trim panel covering the ECU and fuel cutoff switch. There are two plastic flathead screws and a clip you cant see.
4. Ground the terminal on the ground bolt next to the fuel cutoff.
5. Take off the black plastic cover from your ECU wiring and shove the open lead of the cap into pin #57 (if you have a zetec, not sure about duratecs pin #). There are other methods to get the signal (t-tap, splice, cut and solder, etc) but the shoving in the hole method worked fine for me and is 100% reversible.
6. Plug the plug into your aux-in (duh.)

Now turn your stereo on the aux channel and listen. If it is too quiet at full volume, you havent shoved it in pin 57 far enough. I do have to keep it at max volume during tuning to hear over my exhaust. I also have a lot of whining noise like alternator whine, but you can easily hear everything over it. I plan on building a bandpass filter later to fix this.

If you are wondering what knock sounds like using this method, this is a very good clip. In the beginning-ish you hear the very rough sounds of heavy knock that you can hear outside the car, "rocks in a tin can". Then in the middle of the clip it transitions to the "pinging" that is indicative of light, inaudible knock (that can still blow your motor!). I have heard this exact same pinging noise while tuning, so I can confirm this is in fact knock. It has made that noise for me both on high timing and slightly lean pulls.

knock sensor sound with knock CLICK ME

here is the explanation of a "tip-ring-sleeve" connector if you are confused about what i said up there http://en.wikipedia.org/wiki/TRS_connector

This website was particularly helpful:
http://home.netcom.com/~bsundahl/kno...ten/listen.htm
http://home.netcom.com/~bsundahl/kno...nockSounds.htm


Cheers!


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Old 08-07-2009, 01:46 PM   #2
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htat's neat. i never knew it could do that.
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Old 08-07-2009, 03:26 PM   #3
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nice trick and a decent write up ... with sound clip and reference links, no doubt. You da man!
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Old 08-07-2009, 04:13 PM   #4
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..... but why are you pulling timing??? There HAS to be a reason why.... and what about inaudible Detonation.... chances are you couldnt pick that up.
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Old 08-07-2009, 04:39 PM   #5
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I think it might be picking up valvetrain noise. His valvetrain is loud because his clearances are still a bit on the loose side... he's waiting on Karl (aka Massive) to send him some different sized tappets.

I don't know if its enough to cause those problems but I like to hope for the best.
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Old 08-07-2009, 05:07 PM   #6
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As stated, the pinging/twanging/bird chirping sound is inaudible detonation. You cannot hear it normally, but when i listen via this method, it is there. There is TONS of info on this stuff on the web that agrees about this...

ive been waiting on Karl for 2 months so I needed to figure something out so I could tune without the knock sensor on in the tune. This does it, at least enough so I can make the car drivable. I'm still running very conservative timing until I can get my lifters straightened out.
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Last edited by illinipo; 08-07-2009 at 06:25 PM.
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Old 08-07-2009, 05:32 PM   #7
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Using the electronic stethoscope is very simple. You simply clip to the microphone to whatever you are interested in listening to. Noises are transmitted through the metalwork directly to the clip and microphone, making the stethoscope extremely sensitive. To detect detonation, the clip is best placed directly on the block, in the type of place that the factory knock sensors are positioned - no surprise there! Adjust the volume control to give a comfortable loudness level, and sit back and listen. Over the clatter of pistons, valve gear, explosions and gearbox whines, detonation sounds like a sharp "splat!, splat!".

Testing was carried out on an RB20DET-powered C210 Skyline running 15 psi boost and water/air intercooling. Even in cool ambient temps, holding full boost in third gear resulted in some low-level detonation, knocking that was simply impossible to hear from inside the car without the electronic helper. Depending on the location of the microphone clip, gearbox noises, injector clicking, suspension clunks, turbo whistling - the whole lot could be individually identified.
http://autospeed.com/cms/article.html?&A=0353

Part 1 of this article actually claims that this method and a good set of ears can detect knock before a J&S! http://autospeed.com/cms/article.html?&A=0348

More knock audio clips:

http://www.theknockbox.com.au/content/view/8/8/


What knock "looks like" (there is more of this in the links in the first post):

http://www.theknockbox.com.au/content/view/9/8/


Another good thread:

http://www.turbododge.com/forums/f4/...ing-setup.html


The various sounds you hear are all rhythmic. you can pick out individual sounds like injectors and tappets and normal combustion. Then the deto sounds come on like crazy, they are random and sound way different. Hard to describe, just listen to all the sound clips.
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Old 08-07-2009, 05:38 PM   #8
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Originally Posted by 03OrangeSVT View Post
..... but why are you pulling timing???
I point to tappet noise. When I first started tuning I played with the timing for DAYS from 2500-3500. Any load over .4, no matter what the timing, i went as low as -2 and as high as 18 on the FINAL timing after adders and KR... no matter what I did, as soon as I crossed .4 load it would show full KR (whatever I had in the max retard table). I drove the car in closed loop around 10 degrees of timing for a full month because I couldnt trust the knock sensor. It was painful. Just wish Karl would send me those buckets already...
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Old 08-07-2009, 10:11 PM   #9
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Sooo! I would imagine then that the ECU is watching for a specific threshold voltage. Anything over the threshold (RPM based) signals knock (also visible listening to the clips and watching the DB meter). If your tappets are that loose, then they could actually cause the retard (I would think) as the ECU is interpreting the valve noise as knock.
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Old 08-07-2009, 10:51 PM   #10
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I would imagine the ECU does something more complex than that... hopefully does a little signal processing to make sure the noise is in the right frequency range. Thats why not ALL noises will set off the KS, only noises at certain frequency ranges... perhaps valvetrain noise in specific RPM ranges...
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