knock sensors

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knock sensors

Postby AE82 FXGT » Wed Apr 15, 2009 1:27 pm

hey how specific are knock sensors to motors?

I need one for my ae101 gtz and they are all upward of $150

just wondering if I can nick one from another 4age or such.
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Postby themaleman » Wed Apr 15, 2009 1:55 pm

i thinik any 4agze 1 will do, and may need a matching plug. i was told by toyspares that 4age ones are different
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Postby Jason T » Wed Apr 15, 2009 3:07 pm

themaleman wrote:i thinik any 4agze 1 will do, and may need a matching plug. i was told by toyspares that 4age ones are different


Two types early round plug late square plug.

I can help with both types $50 to your door for 93+ square plug style
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Postby AE82 FXGT » Wed Apr 15, 2009 6:22 pm

that sounds great ill check which one i need and get back to you.
Previous: '85 AE82 FXGT, '92 AE101 GTZ, '92 AE101 GT-APEX, '04 SE3P RX8, '05 Mazda 6 MPS, '97 NA8C MX5, '03 GSX250, '08 ZX6R, '13 GROM
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Postby strx7 » Thu Apr 16, 2009 10:17 am

pretty much any toyota engine can donate the knock sensor to your cause as long as its either a) got the right plug or b) comes with a bit of loom so you can join it.
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Postby sergei » Thu Apr 16, 2009 1:19 pm

strx7 wrote:pretty much any toyota engine can donate the knock sensor to your cause as long as its either a) got the right plug or b) comes with a bit of loom so you can join it.


Nope, not true been down that path, and they are all slightly different. I guess they "tune" them to the specific position/noises.
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Postby fivebob » Thu Apr 16, 2009 1:41 pm

strx7 wrote:pretty much any toyota engine can donate the knock sensor to your cause as long as its either a) got the right plug or b) comes with a bit of loom so you can join it.

You forgot the most important one....
(c) they are for the same sized bore

IME Toyota knock sensors are tuned for specific frequencies. These frequencies relate to bore size, so if the bore size is the same then the fundamental knock frequency should be the same, and the knock sensor will probably work OK.
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Postby AE82 FXGT » Thu Apr 16, 2009 1:53 pm

thats the info I was after, i knew how they worked by picking up frequencys and was wondering if they have to be from the same motor or whatever.

This Jason T is sussing one out from another gze so I don't have much to worry about.
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Postby MAGN1T » Thu Apr 16, 2009 1:58 pm

They're nothing more than a microphone in a fancy package. If they've only got 2 wires then there's no way they can have anything fancy in them. You can even hook them up to a preamp if needed and have a listen to what's going on over the top of all the electrical noise.

All the fancy electronics are in the ECU.

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Postby fivebob » Thu Apr 16, 2009 2:23 pm

MAGN1T wrote:They're nothing more than a microphone in a fancy package. If they've only got 2 wires then there's no way they can have anything fancy in them. You can even hook them up to a preamp if needed and have a listen to what's going on over the top of all the electrical noise.

So are you saying that any knock sensor will work regardless of bore size, and that they are not tuned to a specific frequency???
Last edited by fivebob on Thu Apr 16, 2009 2:34 pm, edited 1 time in total.
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Postby BZR4AGE » Thu Apr 16, 2009 2:29 pm

On a side note, this means that a 20V silvertop knock sensor will work fine on a blacktop and vice versa, because they are of the same plug, bore size etc etc?
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Postby Mr Revhead » Thu Apr 16, 2009 2:48 pm

im with sergei and fivebob, last time i tried saying that though i got flamed :roll:

as explained to me by a good autosparky they work by using a piezo (same thing as a gas bbq or fire uses to start) to generate an electrical signal. ecu then processes that signal against preprogrammed data.
same sparky also told me that no, they are definitly not all the same.
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Postby sergei » Thu Apr 16, 2009 3:37 pm

MAGN1T wrote:They're nothing more than a microphone in a fancy package. If they've only got 2 wires then there's no way they can have anything fancy in them. You can even hook them up to a preamp if needed and have a listen to what's going on over the top of all the electrical noise.

All the fancy electronics are in the ECU.

Steve


Every single mic. has got different properties. If you talking about specialised mic that is designed to detect certain frequency, then of course it will be different. I know for sure when you use wrong knock sensor it sometimes can come up with engine light. See the problem is that ECU does not have infinite CPU resources to do elaborate DSP hence they design the filtering into the sensor itself. Car ECU is baicallly a uC and bunch of darlingtons/transisotr drives for output and opamps for input. Same sort of specs as you can get from Jaycar (like those 16MHz/512kB EEPROM 16kB RAM, AVRs or PICs).
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Postby sergei » Thu Apr 16, 2009 3:41 pm

BZR4AGE wrote:On a side note, this means that a 20V silvertop knock sensor will work fine on a blacktop and vice versa, because they are of the same plug, bore size etc etc?


They are probably even same part number. Like many things shared between them.
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Postby MAGN1T » Thu Apr 16, 2009 7:36 pm

Every telephone uses an electret mic. It's a piezzo crystal with a FET built in. They're also polarity sensitive. If you get the wires the wrong way round it won't work.
They're made by the millions and put into different boxes with different names on them just to confuse the customers into thinking that theirs is "special" and worth a lot more than 50c. People in the trade like to talk a load of shyte.

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Postby fivebob » Thu Apr 16, 2009 8:10 pm

MAGN1T wrote:Every telephone uses an electret mic. It's a piezzo crystal with a FET built in. They're also polarity sensitive. If you get the wires the wrong way round it won't work.
They're made by the millions and put into different boxes with different names on them just to confuse the customers into thinking that theirs is "special" and worth a lot more than 50c. People in the trade like to talk a load of shyte.

What has this got to do with knock sensors?

You still haven't answered the question...

Are you saying that any knock sensor will work regardless of bore size, and that they are not tuned to a specific frequency???
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Postby MAGN1T » Thu Apr 16, 2009 9:15 pm

All the circuitry, filtering etc is in the ECU. There might be some minor differences in reponse though between knock sensors, maybe do do with the box that it's mounted in.
Think of it another way, a standard off the shelf electret mic has a frequency reponse of 50Hz to 15KHz which covers your hearing range. Knock might be about 5KHz depending on the motor.
The ECU is made up from pretty much off the shelf parts although the microprocessor is a bit custom and there's some custom hybrid circuits in there also made from standard parts. It wouldn't really make sense to use a special, one off microphone to do the job.
Besides when you wire up a knocklink to your car, the instructions say it works with any knock sensor or if your car doesn't have one, you can wire any knock sensor up to it..... it even works with a normal microphone.
How would you ever know that it's not working unless you hit it with a hammer and monitor the output? How does the ECU bring up a fault code when under normal conditions it doesn't put out a signal. Maybe if it's been disconnected or it's gone open circuit and doesn't draw any current ?

http://www.linkecu.com/products/Ancilla ... /KnockLink

Everyone should have one of these. It will save you from your next unplanned rebuild.

By reverse logic it implies that all knock sensors are pretty much the same.


Only a bit OT.

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Postby fivebob » Thu Apr 16, 2009 9:58 pm

MAGN1T wrote:All the circuitry, filtering etc is in the ECU. There might be some minor differences in reponse though between knock sensors, maybe do do with the box that it's mounted in.

Actually there's quite major differences in the frequency response of narrowband knock sensors used in automotive applications these days. Most ECU's do little, if any frequency filtering. Generally they rely on the resonance of the sensor to generate a strong signal when the frequency is in the range that might signal knock.
Think of it another way, a standard off the shelf electret mic has a frequency reponse of 50Hz to 15KHz which covers your hearing range. Knock might be about 5KHz depending on the motor.

But a knock sensor is not an off the shelf microphone, at least the narrowband ones aren't, and they have a very specific frequency response.
The ECU is made up from pretty much off the shelf parts although the microprocessor is a bit custom and there's some custom hybrid circuits in there also made from standard parts. It wouldn't really make sense to use a special, one off microphone to do the job.

Actually it makes quite a lot of sense. A lot of ECUs do not have the processing power to do realtime FFT calculations to determine the frequency and still have enough grunt to do the job of running the engine. Hence why they use narrowband knock sensors that only output a strong signal in the fundamental knock frequency range, which is a function of bore size ;)
Besides when you wire up a knocklink to your car, the instructions say it works with any knock sensor or if your car doesn't have one, you can wire any knock sensor up to it..... it even works with a normal microphone.

Ah I see, you're making the mistake of assuming that an aftermarket knock detector is the same as that used in production automotive systems. Not everything works the same as the Knocklink. It's cheaper for engine manufacturers to make an ECU that doesn't need to do any signal processing, and simply needs to check the signal when the engine in in the knock window, which is about the 20° following ignition.
How would you ever know that it's not working unless you hit it with a hammer and monitor the output? How does the ECU bring up a fault code when under normal conditions it doesn't put out a signal. Maybe if it's been disconnected or it's gone open circuit and doesn't draw any current ?

There's a big difference between not outputting any signal when it's broken, and not putting out a strong signal when the frequency is not close to the fundamental knock frequency.
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Postby frost » Thu Apr 16, 2009 11:10 pm

man i love these debates, i learn so much. that is all :)
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Postby sergei » Fri Apr 17, 2009 12:08 am

What MAGN1T fails to realise, how little CPU power ECUs have.
They have a lot less than DSP on your fancy Soundblaster card.
Also unlike normal computers, ECU's operation is time critical.
There is no way you are going to process real time 15kHz signal with say a typical 16MHz 8bit CPU, while calculating fuelling and ignition and also doing various I/O. You cannot pull "RealPlayer - buffering" on running engine.
It looks like you never programmed a micro to know that you don't have much to play with.
Imagine how many sensors you have. you have to poll every analogue sensor output, sample, "normalize" it etc.
Say you have 3-5 analogue inputs, and 2-5 timing inputs, now those timing inputs better not to be missed, not only that you have to calculate the length of every pulse. If you put these into numbers the 16MHz would be barely enough and you want to do DSP on knock input?

I wanted to built a hand held digital oscilloscope based on a 16MHZ AVR, then I quickly realised that I simply don't have enough CPU cycles to reliable sample stuff over 100kHz (at least in written C), and at that frequency everything would look like square wave, which would make this scope pretty useless (maybe good for automotive use I guess). Anyway at this clock speed you have a few microseconds to do your stuff then to move on on another input.(I realise there are internal timers and interrupts but they don't help if you have only 20-50 instructions per sample).
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