Author Topic: Knock sensor add for tuning purposes? (Read 5610 times)

Aka-e30 · « **on:** February 18, 2013, 08:23:35 PM »

So i have a theory. Im planning on boosting my m42 (e30) as you all know, only the e36 m42's came with knock sensors and our old school ones in the e30's did not. That being the case, im wondering if its possible to mount up a knock sensor on the block wired in to some sort of digital counter so as i tune the ignition map i can monitor the knock count. Has anyone done this already or am i going to have to pioneer this? ha.. it would be nice to see how it was set up if it has already been done.

bmwconnect · « **Reply #1 on:** February 18, 2013, 11:20:38 PM »

Quote from: Aka-e30;120244

So i have a theory. Im planning on boosting my m42 (e30) as you all know, only the e36 m42's came with knock sensors and our old school ones in the e30's did not. That being the case, im wondering if its possible to mount up a knock sensor on the block wired in to some sort of digital counter so as i tune the ignition map i can monitor the knock count. Has anyone done this already or am i going to have to pioneer this? ha.. it would be nice to see how it was set up if it has already been done.

There is already devices on the market that do just this. headphones and a microphone in the engine bay is also very effective and I do it often when tuning

MLM · « **Reply #2 on:** February 19, 2013, 03:30:20 PM »

One such device

http://www.linkecu.com/products/TuningTools/knocklink_g4

Aka-e30 · « **Reply #3 on:** February 20, 2013, 05:46:01 PM »

@bmwconnect Thank for the suggestion. I might have to go with the headphones. That knock link is pretty sweet if only it didnt cost $235.00. I was thinking maybe it would be possible to get a knock sensor from the local pull apart and wire it in to a counter or i suppose you could do a light like the Knock Link. Cuz a knock sensor is just a piezo electric sensor so when it detects a vibration/pressure or in this case, Knock it generates an electrical signal (voltage). So im thinking all youll need is your ground and a your knock sense or "signal" wire wired in to your light and once it sees knock it should light up. you may need a 12v supply somewhere idk.. I think im gonna play with this and see if i can come up with something. If i do ill post it up for all to see.

romkasponka · « **Reply #4 on:** February 20, 2013, 06:28:12 PM »

The good thing with link is that you can log signal to ECU (megasquirt or other) and you will know at what exact time you have knock and later you can tune your ignition. By hearing I am not sure you can be so precise.

Aka-e30 · « **Reply #5 on:** February 20, 2013, 09:53:29 PM »

Yeah data logging that would def be an added bonus. I suppose $235.00 Really isnt all that bad for all that you get. I def like the system but im just stuck in my DIY tendencies. ha If i just had something to moniter knock in real time that would be better than nothing. Anything is better than nothing. ha

wazzu70 · « **Reply #6 on:** February 20, 2013, 11:34:53 PM »

The issue is you need to monitor a certain frequency range for knock. Everything else is just standard operating noise. You will also need to know what phase of the crank rotation the knock sensor needs to be looking (it ignores the times monitored cylinders are not under combustion.)

Monitoring knock is incredibly complicated through software. You need to know when to look for the signal, what frequency knock is in for your engine, and you usually need to run the recorded data through a FFT to eliminate the crap. This is what the Link does, its way more than just a LED!

Headphones like mentioned work wonders, and your brain can even process the sounds way better than coming up with a control algorithm. Seriously, most tuners use stethascopes for a reason! Much easier!

Look up "det cans" for more info. Something like the J&S knockbox or the Phormula unit are other more sophisticated options.