DIY knock detection

[Akane]

Has anyone built a DIY knock detection device?

I've built one using a MD Walkman I had lying around, a PC mic, and a pair of headphones, and a clip, similar to this:

http://autospeed.co.nz/cms/article.html?&A=0353

I know what I'm suppose to listen for, but I tried it both in the road legal suzuki, and the MR2 that has a VERY lean running tune right now (NBO2 showing full lean under boost lolz)

But I'm not hearing anything in both cars, especially on the suzuki's 3rd gear pull where max torque should occur, but instead I'm getting a lot of engine noise, something that sounds like piston slap over the headphones.

the MR2... I just ain't getting anything except brommm ER OMMMM ER ER ER OMMMMMMMMMMM pshhhhshshshshsh

has anyone built anything similar to this, did you go the mic route or the knock sensor route? I've read directly wiring to the knock sensor ain't as good as having a mic.

Any input is greatly appreciated, thanks!

[steve murch]

there was one in a zoom mag afew years ago, built one it worked well and im still using it.
uses the memcal knock board out of a gm computer then made to run a led for detection using the gm knock sensor.

[Akane]

Hi Steve

I have a Power FC which shows knock on the hand controller, but I'm worried that it's not accurate or responsive enough to use it as a tuning device, but by the sound of things your GM board that you've built should be similar to what the Power FC will show? If that's true then that means I can use the Power FC's knock display as a tuning tool?

Thanks

[QikStarlie]

i use a donut style knock sensor with mine connected to a small audio amp and headphones inside earmuffs. ear muffs is a good idea as it blocks out the background noise. you do get alot of valve and engine noise coming through, some engines are louder than others. you just have to know what to listen for over all that. if you've never heard knock through your detset, find a car that you dislike advance the timing till you hear a new noise... best way ive heard it discribe is if you were to put a layer if tin foil on top of cup an flick it. sounds very similar


lazy edit:

i would always listen for knock. far better than any readout.

[steve murch]

Hi Steve

I have a Power FC which shows knock on the hand controller, but I'm worried that it's not accurate or responsive enough to use it as a tuning device, but by the sound of things your GM board that you've built should be similar to what the Power FC will show? If that's true then that means I can use the Power FC's knock display as a tuning tool?

Thanks

power fc must stipulate what sensor to use?
all knock sensors are pretty much the same but its the frequency range they work in that's most important with whats calibrated in your ecu/hand set

[Akane]

i use a donut style knock sensor with mine connected to a small audio amp and headphones inside earmuffs. ear muffs is a good idea as it blocks out the background noise. you do get alot of valve and engine noise coming through, some engines are louder than others. you just have to know what to listen for over all that. if you've never heard knock through your detset, find a car that you dislike advance the timing till you hear a new noise... best way ive heard it discribe is if you were to put a layer if tin foil on top of cup an flick it. sounds very similar


lazy edit:

i would always listen for knock. far better than any readout.

so you're listening from the knock sensor itself, I might try to go that route instead of a normal PC microphone, it sounds like a better choice since it'll cut off all the unnecessary frequency. Yeap that's what I think too, a listen will be better than a readout.

power fc must stipulate what sensor to use?
all knock sensors are pretty much the same but its the frequency range they work in that's most important with whats calibrated in your ecu/hand set

the Power FC is vechicle specific, so it's tuned to the factory knock sensor's frequency. Which if i remember correctly, is around 6.5Khz~ for 86mm bore 4 cylinder engines.

There was a long thread on mr2oc where people replaced the factory sensor in favour for the GM sensor, and someone thrown it on a scope and found out that the GM sensor is not suited for 3S-GTE applications.

[BlakeNZ]

FRom what i understand,the power fc is adjustable in terms of you can choose what setting the ECU regards as a genuine knock event. from factory, i think apexi are set at 60 from memory, which most people run them at,but my mate runs his at 30 on his 3sgte, due to the fragile nature of this motor's ringlands.

[strx7]

to test it, have the headphone going and have someone tap the knock sensor or the bolt going thru it with a small spanner or similar, the knock you will hear is very similar to that. you also need to be able to distinguish ignition missfire from knock

[steve murch]

trying to work a any sort of detonation can be hard even with the best gear, do yourself a favour and learn how to read plugs to back up what your hearing or seeing.
if you can master that youll learn allot more than just what det maybe doing.

[ChaosAD]

You will want to use a wideband sensor like the one quickstarlie mentioned, not a narrowband one.

It is possible to share the knock sensor with the stock ecu but your amplifier will need to have a high impedance.

If you do a search theres a few audio clips floating around the web to give you an idea of what knock sounds like through a knock sensor.

[Akane]

The Power FC is not adjustable in terms of how to hear knock, the only thing that's adjustable is when the knock warning should come on, the factory setting is 60

Yeah I've heard a few clips on the internet, sounds like marbles hitting each other.

Steve, I've been reading the plugs but the tune is so different, all I get is black sooted plugs, the tune is for my old Gen 2 3S-GTE, now I've put in a Gen 3 in there, removal of T-VIS and different head design alltogether, makes things wrong.

But with a wideband and some DIY knock detection I'm sure I can tidy up the tune enough on the road that I can drive it to a WOF place at least.

Wideband is next on the list of the things I need to purchase.

ChaosAD, do you have a link or something that explains the high impedance thing in more detail? I have read that in order to wire directly to the Knock sensor, I need to wire in a 10k resistor only to prevent feedback to the ECU from my amp, which in this case, my Walkman with both MIC IN and Headphones output.