Kingtal0n

I have no computer in my car. I would like to use a Knock sensor anyways, Just to "listen" to it.

my question:
#1: If i went to Auto parts store and bought a knock sensor, Which one should I buy? there are several types for 305's 350's each year etc... I have a radical engine, I would like a knock sensor that isnt SUPER sensitive... Would a 1992 350 TPI knock sensor do it?
#2: Where does it go? I have looked at then, and it looks like they screw into a water plug hole?
#3: There appears to be only 1 wire from the knock sensor. What runs through this wire to tell me it senses a Knock. Voltage? Ground? I have heard they ground when they "hear" a knock.
If this is true, whats keeping me from buying one and screwing it in then connecting it to a voltage sensor and checking for ground / voltage?

#4 anything else I need to know?

Ozzy88GTA

You could try tinkering with all kinds of gadgets and maybe you could come up with something to listen to knock, or you could spend about $142.99 and buy an MSD Knock Alert. Jegs has it and it might be what you are looking for. Go to the link for more info.
http://www.jegs.com/cgi-bin/ncommerc...67&prmenbr=361

This is your best bet since a knock sensor is calibrated for a specific type engine. An engine is very noisy inside and the knock sensor is tunned to ignore all other sounds except for those caused by detonation.

-Ozzy

Kingtal0n

Thanks! thats exactly what Im looking for! the price is just scary... I need a speedometer too and thats the price of one!

I was just hoping somone might know what kind of signal those sensors give off... Sigh* i guess Im just going to have to buy one and hook it to a volt meter and find out eh?

Darn knock sensors are $40!!! Almost worth buying that kit... hmm...

Ozzy88GTA

According to this article the sensor does put out a voltage when the tuned frequency is detected:

http://www.autoshop101.com/forms/h38.pdf

I would use an analog multimeter to test it first and see if it works. One question, how good are you with electronics? I ask because I have found some electrical schematics that use a small voltage input and use an LED bar graph to display the result. One example is a Fuel/Air ratio meter :
http://www.gnttype.org/techarea/images/02sensor.gif

Here are more for the DIY: http://www.california.com/~eagle/instr.html

But here is the knock sensor circuit if you want to built it yourself:
http://www.gnttype.org/techarea/proj...ck/circuit.gif

original site: http://www.california.com/~eagle/knock.html

Hope you get it figured out,
-Ozzy

Kingtal0n

Wel I did some TESTING and it turns out my 1992 350 TPI Brand new KNOCK SENSOR does NOT Emit voltage when it detects knock.

Instead, it simply changes its resistance to ground.

I read 99.4K Ohm Resistance at base levels (no knock)
and by simply banging the thing on a peice of metal I got readings of between 110K Ohm - 190K Ohms of resistance to ground.

There is no voltage and no continuity from - to + ... In fact By connecting a 12+V Wire to the knock sensor (while grounded) it simply gives a slight "spark" But barelly audible and not detectable by sight easilly.

Im going to return the knock sensor and test a different one, from a different car.

any Idea what Car / Year would have a knock sensor that emits voltage? I have no idea how to work with resistance to ground.

Kingtal0n

I just read that:
"This signal is about plus and minus 2 volts and the duration depends upon what is causing the knock. The signal is about 5 thousands of a second. To light an indicator we have to stretch this pulse to something much longer. "

From a website. I wonder if this is why I cant see the voltage with my meter?

Danno

Remember one thing guy's, the voltage source for the KS comes from the ECM. The ECM through usually a 4.7k-10k ohm resistor supplies the sensor with a 5 volt source. Thread end is ground and the detection of vibration in the 4-8hz region causes the resistance to change and thus changing the voltage which the ECM reads to correct timing. I know of no sensor that generates it's own voltage other than the O2.

Kingtal0n

ok whoooaaa now im confused***

Voltage is generated by the passing of current right? I mean if you have no where for the current to go, you cant have any voltage or resistance right? I know its a crude way of looking at it, but am I right?

The Knock sensor apparently alters resistance to whatever source it is screwed into. I say resistance to GROUND because, well, screwing the thing into the block means its automatically grounded. So we can safelly assume that if the ECM wants to read the knock sensor in a "voltage" state, it can simply use any grounded source as an indicator. Am I on to somthing or totally screwed up?

Now, the knock sensor only has 1 wire. this 1 wire also is absolutelly NOT a ground signal, but does generate a resistance TO the grounded signal, I guess that means that even though you cannot use this wire AS a ground (say, to light a bulb) it STILL carries a ground signal, but not NEAR enough to do much of anything at all. This explains the Tiny itsy bitsy un-seeable but audible spark you get when you apply 12V+ to this wire, while the knock sensor itself is grounded.

All in all, Im guessing here, but, I think after reading this:
<b>The ECM through usually a 4.7k-10k ohm resistor supplies the sensor with a 5 volt source.</b>
im GUESSING that If i bought a resistor from radio shack.. applied it to the voltage side (say 12V+?) and hooked it up to that 1 Wire, We would see a fluctuation (?) in voltage on the sensor side? this would technically mean, since the resistance goes UP (voltage goes down) we will see a drop from 12V+ down to... whatever... and if that drop is more than say... 1V it will be enough to visibly dim a lightbulb, and thus every time the knock sensor "hears" a knock our lightbulb will DIM.

Of course, I could be dead wrong I was just making this up as I went along. I'm really trying to avoid spending $150 on an MSD knock sensor setup when I could possibly make one myself.
Somone correct me cause I know im incorrect somwhere. Somone who has done this without making a curcuit board or modifying somthing HUGE please chime in. Or somone with an idea or a used MSD knock sensor thingy that want to sell me :-)

Tim Burgess

The knock sensor actually does produce an AC voltage. You can think of it is as a special "microphone" that listens to the noise made by the engine. The output of the sensor may be viewed on an oscilloscope as an AC waveform. The sensor may not be used by itself to detect the onset of knock caused bby detonation or preignition. A circuit is required to interpret the output of the sensor and determine if the frequency spectrum being received by the sensor contains any components of the onset of knock. Although I have not tried it, I would imagine that a knock sensor may be used with a ESC (Electronic Spark Control, or "knock sensor buffer") box, that was used from '82 - '89 as a building block to build an onset of knock detector. (In '90, the ESC function was moved internal to the ECM). I don't know for sure what the output of the ESC module looks like, but my guess would be a voltage whose presence indicates the onset of knock.