DIY knock sensor HELP| Grassroots Motorsports forum |

dean1484 GRM+ Memberand Dork
3/14/10 3:27 p.m.

I know that they "listen" to the sound and the trigger something in the ecu to retard timing.

I have a couple knock sensors from 951's laying around and would like to hook it to my MJLJ ignition control. The idea is to some how get a signal from the knock sensor that I could use to trigger the use of the second timing map that would lower the timing across the board in the areas where knock can really damage things. (idle probably would not be affected). The trigger would be through a relay that holds the second map in effect for say 10 seconds???? before reverting back to the original map.

It is not as "smart" a solution as factory computer controlled units but it seems like it could be a reasonable solution. So how do you get an output form a knock sensor that you can actually use with an ignition control. Getter yet a output that has a scale that I can use (0-5 volt) (0-13V). The best would be something equivalent to a temperature sensor as the MJLJ already has an input for that. That I am not using)

So if I could use the temperature sensor input as it has a scale and I can set thresholds for triggers of a timed relay (say one with a 10 second hold function) that I would then have activate the circuit that causes the MJLJ to swap maps.

So how can you get a usable output from a knock sensor? Are there cheep knock sensor controls (similar to WBO2 controllers) out there?

dean1484 GRM+ Memberand Dork
3/14/10 3:31 p.m.

I have been looking at this just instead of the light use it to trigger the map swap circit?

http://tunertools.com/articles/KnockLite.asp

alfadriver Dork
3/14/10 5:43 p.m.

here's the hard point- basically a knock sensor is a microphone. How the ECU decides that there is knock is that it takes the signal, does some basic signal processing (like Fourier transform), and look for specific frequency spikes. On a dyno, one induces knock to know how an engine "sounds", and then that is the point where you start taking action.

So if you know if any of the "mega' systems are capable of processing high frequency sounds- perhaps it's possible. But to really calibrate it, you'll have to force it to knock, so you know what it sounds like.

Eric