Knock Knock, anyone home?

[DGGT6]

Greetings Gents,
Has anyone had any success in making a bosch 2 wire knock sensor work with a GM knock module and a MS2?
I get a small AC voltage when I tap the knock sensor and I get a signal from Tunerstudio when the MS wire is  from the module is grounded. So it appears that the sensor functions, the (brand new) module functions and my MS2 is correctly setup to detect a simulated (grounded) knock signal.
It just doesn't register in Tunerstudio when I hit the sensor with a hammer (or drive the car).
Any thoughts,  please?

Thanks,
Doug

[Nick Jones]

Very tricky subject this one.  I remember reading about when I first started out with MS (2004!).  I was keen to implement knock sensing as the Vitesse on carbs and clockwork dizzy was a world class pinker.  However, after extensive reading it got filed in the "too hard at current knowledge level" bin and then, when FI more or less completely cured the pinking and 3D ignition finished the job, forgotten about.

There is LOADS on line about it.  Some quite contradictory.  

http://www.extraefi.co.uk/pdf/knock.pdf

This is a useful little document that starts by pointing out that the sensors sensing frequency needs to match the characteristics of the engine....... ah, right.  Which kind of explains why it seems to be more successful on cars where MS is substituted for a factory ECU and hooked up to a factory-selected knock sensor.

Why exactly do you think you need a knock sensor?  Get your mapping right and it won't pink/knock anyway.  Ok, it would mean you could run a bit closer to the edge but.......

Nick

[RobPearce]

Knock detection is hard. Very hard. On some engines it's damn near impossible, which is part of the reason the Rover K-series never had knock sensors fitted. Based on my (admittedly limited) experience of knock detection over 27 years of writing engine ECU code, I'd say you'll almost certainly need two sensors for a Vitesse, if not three, and very careful filter setup (frequency tuning).

As Nick says, why do you need one? If you're tuning a single engine, just set it up by ear. Knock sensors are there for optimal performance across a range of production tolerances. Well, and varying fuel quality, but you can just take more care where you fill up.

[DGGT6]

Thanks guys.
My basic premise/reason for Megasquirting my car was so that I could log what was happening then adjust accordingly rather than guessing by ear or sanding carby needles or changing dizzy springs and millions of trials. Something that I have discovered thanks to the MS is that the water temperature coming out of the radiator at 90kph gets down to about 70C! I currently have a 90C thermostat installed so there is a 20C difference. The same differential should apply to a 83c stat.
I was hoping that a knock sensor would show me "exactly" where to adjust the timing. I don't intend to rely on it to "save my engine" just tell me where she is knocking. I can here it easily at the moment but I don't have a passenger seat for someone to sit in and adjust while I am driving.
As mentioned there is a huge amount of contradictory  info on line. For instance with the American cars sharing the same sensor and module despite the bore size varying immensely!
I thought the best thing was to give it a shot and find out for myself. So far I have an engine that knocks very well, a sensor that generates AC voltage, Tunerstudio displaying a simulated knock/grounding, a new  sensor module that doesn't seem to transmogrify the sensor signal to the MS signal. I was hoping that as usual it was I that have made the mistake in wiring etc rather than the components not actually working.

Cheers,
Doug

[RobPearce]

The problem is that you need many hours of dyno time with an independent indication of the presence of knock just to set up a fully working knock detector to accurately identify knock on a given engine design. It's one of those things where a computer finds it much harder and more confusing than an experienced eardrum. And in the process of setting it up, you'll have found all the regions where the sensor just won't work. But more usefully, you'll have actually done all the tuning work that you think a knock sensor might help with.

[DGGT6]

Hi Rob,
I can hear where the knock is, I think I just need to connect the the (correct?) bits together correctly and see if I get a reading when I hear the knock.

Cheers,
Doug

[mpbarrett]

you need to look at the signal coming from the sensor (or amplifier) output to see if there is anything there. If you don't have an oscilloscope try using you PC (assuming you have one). There are some nice software solutions that us the PC sound card as an A/D and then displays the signal. Feed the signal into the mic or line input and then run the program. Its bandwidth will be limited but you should see something. If you cant see any signal from the sensor when its knocking then the MS will never detect it.
Actually if its a Piezo device you wont see any thing without the amplifier as its needs a very high input impedance amplifier....

I will leave the issue of if it worth doing/possible to Nick and Rob....

mike

[Nick Jones]

Knock sensors are usually piezo based devices and are basically microphones.  One trick is to hook them up to headphone amps or even directly to crystal earpieces so you can hear what is going on.

I appreciate that this isn't what you are after though.  I suspect that the signal you are getting is either to low powered or too short duration for MS to pick up.  One thing you ought to check is whether you have damping turned on on the input channel you are using as with damping enabled you might struggle to detect short spikes.

Nick

[poppyman]

Quoted from Spitfire6

Who's There?

Dr,

[poppyman]

Spoilsport

[poppyman]

Cluck Cluck?

[poppyman]

Definately