Plug and play knock sensor listening harness. Is it really knock?

[Turbo_Steve]

On many of my previous turbo cars / builds I have relied on a knock sensor listening device so that I can listen to the engine and know for sure if any kr that shows up in data logs is truly knock or if it is something else. I have always had great success with this method for tuning as you can typically hear faint knock before the knock sensor will show it as KR in the ecu. The factory knock sensor has a minimum threshold but the mic/sensor on the block is far more sensitive than this threshold. Also if you are having random or phantom knock you can data log, drive and confirm by listening if you are really experiencing any detonation.

Plus as a bonus you can use your car's speakers if you have an aux input so you can listen without having to wear headphones or stare at your datalogger / AP. You hear knock, you take your foot out of the throttle faster.

The big problem with doing this is tapping into the oem harness. The concern is that over time corrosion or interference can occur with the precious knock sensor wiring and cause the ecu to not react to quell knock.

The solution is a nice tap in plug & play harness with properly soldiered connectors that will not interfere with the ecu but will allow you to listen reliably to what your engine is doing.


I have finally located both sides of our knock sensor harness plug and i can build a relatively inexpensive harness for tapping into the sensor and would provide an audio cable that can be plugged directly into the aux input for the radio. You could also add on an inline battery powered headphone amplifier and add pair of noise cancelling headphones.

I unfortunately have to order the male knock sensor plug in bundles of 20 so the costs for doing just one of these harnesses for myself is pretty expensive.

Would anyone else be interested in these harnesses if I were to go ahead and order the parts and build them? I can get mod permission and set up a group buy if there is any interest. I am guessing 30-35 per harness which is pretty reasonable. It will include the t-tap for the knock sensor fully weatherproofed and shrink wrapped with the proper capacitors for tapping into the sensor without interfering. It will also include the proper length audio cable to run from the engine to the audio input.

If there isn't enough interest I am going to skip the plug and play option and just soldier it in to my sensor harness.

Here is a basic example



Thoughts and comments are welcome

[Tokay444]

We can adjust the minimum threshold in atr I believe.

[Turbo_Steve]

Originally Posted by Tokay444 We can adjust the minimum threshold in atr I believe.

Yes, but that only causes more instance of timing to be pulled do to random engine noise and shit being loose in the engine compartment.

[Snip]

Sounds logical.
Nothing new to my ears, my colleague who is from England, and spent time in the rally scene there, said the good tuners already worked like this, while tuning the car, wearing headphones and listening to the engine physically

[Turbo_Steve]

Add this
FiiO E6 Earphone Headphone Amplifier Portable Amp USB Rechargeable Battery | eBay
And this
Noise Cancelling Headphones 3 5 Jack Audio Plug Connector Wired Stereo Headset | eBay

And you could have a complete headphone listening setup similar to the knock ears but at 1/8 the price

[speed23]

I would be interested!

[Blown_Dan]

Interesting... If the price is as estimated, I may consider one.

[rfinkle2]

I'm going to try a little less sophisticated approach and I'll let you guys know how I make out.

[Turbo_Steve]

Lol.... Can I borrow that? My mom's Honda Element has a terrible engine rattle at idle. Having a hard time pinpointing it.

[rfinkle2]

Originally Posted by Turbo_Steve Lol.... Can I borrow that? My mom's Honda Element has a terrible engine rattle at idle. Having a hard time pinpointing it.

Believe it or not, some guys actually like using this over a filtered electronic set-up.

A loooooooong time ago, Dustin mentioned that a Subaru friend of his uses these too.

DIY: Det Cans - GTRPWR Forums

[Turbo_Steve]

I bet it works well. How does it attach to the block?

[rfinkle2]

Originally Posted by Turbo_Steve I bet it works well. How does it attach to the block?

A bolt and a 1/2 inch piece of copper pipe.

Thanks to Zacho on the gtr forums.

[Turbo_Steve]

Cool simple setup. I am going for something a little more inconspicuous that can be permanently installed here.

[rfinkle2]

Originally Posted by Turbo_Steve Cool simple setup. I am going for something a little more inconspicuous that can be permanently installed here.

You mean 3/8 air hose with giant noise cancelling headphones is awkward? LOL

[chaser27]

Originally Posted by rfinkle2 Believe it or not, some guys actually like using this over a filtered electronic set-up. A loooooooong time ago, Dustin mentioned that a Subaru friend of his uses these too. DIY: Det Cans - GTRPWR Forums

Thanks for the idea Rob!

[rfinkle2]

Originally Posted by chaser27 Thanks for the idea Rob!

Hell yeah. Wasn't my idea but I'm looking forward to trying it out too.

[chaser27]

I'm using a slightly smaller tube than he was, I figured it would be better for picking up on the higher frequencies. We'll see how it works

[Lex]

Once you train your ears to the frequency of the knock it will be easier to spot above engine noise at low and medium RPM but at higher RPM it will be difficult as the engine gets quite noisy. Using the KR reading as a guide to train is a good idea.

The knock sensor is a wide spectrum one in this car. This means that it picks up all the noises coming through the block. The filtering is done at the ECU compared to the older style single wire sensors that were already tuned to a particular frequency and ringed like a bell at the given frequency. The knock frequency is roughly determined by the size of the bore of the motor.

Here's the next level to this cool little project. If you put this through the MIC in your PC and you're able to capture the microphone output cleanly enough, you can perform some FFT (fast fourier transform) on the noise and start isolating the frequencies you're looking for with software. All that FFT does is allow you to see the sounds frequencies and their amplitudes at a given frequency.

sndpeek : real-time audio visualization

The knock frequency of the DISI is around 6.5kHz so this is a good starting point to look at.

[rfinkle2]

Maybe you could build a time machine too.

Induce some light load knock and watch the AP. Probably train your ear in about 10 seconds.

https://www.youtube.com/watch?v=GGJZ...eature=related

[chaser27]

I just need to put a bigger hole in the copper and find a place to bolt it up and test, but I think it'll be pretty solid.
I'm going to test it with and without the foam in there. I'm guessing it will actually absorb the longer wavelengths, but we'll see.

[Turbo_Steve]

Went ahead with ordering the connectors for this. Going to build a test harness and report back.

[Turbo_Steve]

Had some overnight parts from Japan show up today.

Connectors are here.

[Turbo_Steve]

Built my first test harness. Going to test it out tomorrow.

[Turbo_Steve]

Test went very well. The audio was very clear with no interference. The only thing that sucks is the di injectors are very noisy. Running something similar on my port injected duratec focus you don't get any injector noise really. I gues since the injectors are 6 inches further from the knock sensor and have plastic bodies. A metal body injector bolted to the head with a metal crows foot is certainly going to be noisier.

Although once you get used to the injector noise it's not so bad. I drove at only part throtlle for this test. I used to always get those little .3-.7 kr at part throttle from time to time. I noticed that I could hear a distinct detonation sound over the injectors right at the moment I would see the slight kr on the AP.

I also drove at cruise long enough for the ecu to try to advance timing to maximize fuel economy. I have logged this before to try figure out why I was getting 5.0+kr at cruise randomly. It is definetly part of the ecu trying to advance timing to test the threshold for the best fuel economy possible. And since it is at part throttle it won't hurt the engine.

During my drive I was lucky enough to have this happen and I could clearly hear a lot of engine knock through the speakers and sure enough 5.6 kr popped up on the ap.

I am extremely pleased with this outcome. I am going to play with it some more and try get some audio recordings posted here. I also am going to analyze the frequency range of the injectors to see if I can Isolate the injector noise by building a simple inline filter.

[Turbo_Steve]

Looks like the frequency range of the injectors is between 2.2-2.9khz. Going to try build a filter to block out anything below 3.5khz and see if it kills the injector noise. Frequency of the knock should be much higher. Should be able to hear this part throttle kr as a test.

[Lex]

Nicely done. So the knock sensor is accurately detecting knock. Are you using the aux input to the car's stereo or headphones?

[Turbo_Steve]

Aux input. Works very well.

[Turbo_Steve]

Going to need some extra connectors for this, but If I were to run one of these guys inline with the audio it should kill all of the injector noise but allow the knock noise to pass.

2 Harrison Labs Fmod 3500Hz HP High Pass Super Tweeter Electronic Crossover USA | eBay

Got a pair on order and will report back what I find.

[Mattyhawk1]

Originally Posted by Turbo_Steve Going to need some extra connectors for this, but If I were to run one of these guys inline with the audio it should kill all of the injector noise but allow the knock noise to pass. 2 Harrison Labs Fmod 3500Hz HP High Pass Super Tweeter Electronic Crossover USA | eBay Got a pair on order and will report back what I find.

That looks like a good option for a filter. Nice job on this project, I'm already excited just on your results so far

[chaser27]

So I finally got around to trying my home Depot special knock ears today. Maybe I listened to too much loud music growing up, but I could BARELY hear anything going on through them and the little I could hear scared me because it sounded like "pennies in a can" but ended up just being injectors.

I think I want to try what @Turbo_Steve; is doing. Can't remember, but do you have a list of everything you needed? It looks like a fun project.

[Turbo_Steve]

I will be updating soon. Having some promising results. I think I have the high pass filter figured out. Going to grab some capacitors to testest it out this weekend. I have filtered out most of the injector noise simply by wiring a 5.68uf capacitor inline. Just going to try a slightly bigger one and all the injector noise should be gone.

[chaser27]

BUMP for updates

[Turbo_Steve]

Update is that I have become distracted by this...







Building a powder coating oven.

I have the capacitor I need to test out, but have not done anything with it yet. Sorry to disappoint. I have ADD or something and I move from project to project without finishing things it seem like. I began building this powder coating oven like 3 years ago and decided it's time to finish it. I am now a lot closer to being done but my mind is already wandering towards another project.

[chaser27]

I have the same problem. Told my girlfriend the other day I need a new project and she listed off 5 I hadn't finished yet. haha

[TiGraySpeed6]

[Jackis]

Were powder coating oven ever finished LOL ?
Looking for some updates over analogue KR listening, cause thinking of quite the same thing.

[PurplFox]

Originally Posted by Lex Once you train your ears to the frequency of the knock it will be easier to spot above engine noise at low and medium RPM but at higher RPM it will be difficult as the engine gets quite noisy. Using the KR reading as a guide to train is a good idea. The knock sensor is a wide spectrum one in this car. This means that it picks up all the noises coming through the block. The filtering is done at the ECU compared to the older style single wire sensors that were already tuned to a particular frequency and ringed like a bell at the given frequency. The knock frequency is roughly determined by the size of the bore of the motor. Here's the next level to this cool little project. If you put this through the MIC in your PC and you're able to capture the microphone output cleanly enough, you can perform some FFT (fast fourier transform) on the noise and start isolating the frequencies you're looking for with software. All that FFT does is allow you to see the sounds frequencies and their amplitudes at a given frequency. sndpeek : real-time audio visualization The knock frequency of the DISI is around 6.5kHz so this is a good starting point to look at.

An FFT on a car motor would look crazy. You have me thinking about Creating a set of points for my vib equipment to see what that looks like. Side note have you ever tried to make a FFT from a raw waveform with out software. That shits a pain in the ass

[HeadSosse]

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