knock sensors and watching knock

[Celica RA45]

have or has any one on this forum played around with real time knock sensing

 

[Roman]

I'm using it with a Link G4+

 

Essentially how it works with the Link. You set ignition timing to settings where it definitely isnt causing any knock.

 

And then you measure how much "background noise" the knock sensor naturally makes at each rpm and load combo.

Then you add about 20% on top of this as the knock threshold.

This is a graph showing the knock threshold (in Red) and the knock sensor output levels on each cylinder in grey and purple at various rpm and load combos as the car drives.



If one of the grey or purple lines goes up above the red line, that's how the ECU interprets knock happening and starts pulling timing out. (you can see two examples of this, middle of screen)
Only problem is that if you have engine bay rattles or go over big bumps in the road, it can sometimes falsely register as knock.

At some load/rpm combos though I find that either the background engine noise is too loud, or the knock sound is too quiet so its hard to distinguish one from the other.

I've currently got mine set to run between 1500rpm and 5000rpm, mainly for purpose of advancing timing at cruise conditions for good economy. But still being able to pull timing back to a sensible level if something goes wrong.

My understanding is that a 3S with standard crank etc has a "deadzone" where you cant measure knock due to natural block vibrations matching the knock signal somewhere around the 6krpm mark.

If you set a maximum ignition retard for knock timing of say 10 degrees, then see that your ECU has pulled 10 degrees timing out at one point. then you know that you need to increase your knock threshold value rather than reduce ignition timing. Because there's no way that an engine would need that much timing pulled out to prevent knock.

It's a work in progress for me, still trying to find the best values to work with.

 

Currently running a Bosch style wideband sensor filtered by ECU to the 6khz range.

[Celica RA45]

been using the m800 motec knock sensor ,we have changed to 7 kilohertz and take out any knock in any cyl range all the way through the rev range .i am now using 30 % ign timing from  about 2400 rpm all the way through to 9000 rpm it makes more hp and torque

,i have also sacrificed top end hp for more down low .

use to have 60 kws at 4500 now 108 kws,,, at 9200 use to be 204 kws now its 185kws .the car is so more responsive as of at the end of the day you are only up at 9200 for a short time ,

have also done  knock on both 4into 1 and try ys and its better with the 4 into 1 

[RUNAMUCK]

Interesting thread.

I have little of value to add except that a bloke on a forum.I'm on fitted a link.knock.block to.his big block after popping a head gasket of some such.

He said it just told him.he was knocking all the time, and once they had his $ link didn't want to.know him.

Perhaps it was a background noise issue given How primitive his dinosaur power plant Is?

[Celica RA45]

dave you would need a chassis dyno to set up knock the best ,to see what the motor is doing in real time 

[Roman]

dave you would need a chassis dyno to set up knock the best ,to see what the motor is doing in real time 

 

Yeah problem is though, that when you're actually driving the car the background knock noise increases. So need to test it in real conditions I reckon.

 

I had a bit more of a play with this tonight, lately I've been getting a strong knocking noise even though my timing has been more conservative than previously, and AFRs on 14.7 during knocking conditions.

Looking at the knock detection it seems to be primarily knocking on #3 and #4, if I let it pull out up to 15 degrees timing it was pulling the timing right back to only 2-3 degrees before TDC.

But only around the 2500-3000rpm mark.

Didnt seem to make sense, but I advance timing more than that and I can hear the knock myself just driving the car.

I thought it might have been VVTI timing, but adjusting that one way or the other doesnt make a difference.

I pulled the spark plugs out as I havent checked them in a very long time.

Looks like they are due for replacement, I think they've had a hard time with a few retunes of the engine and also the time that the spark plug valleys filled up with oil due to half tightened valve cover haha.

Will be interesting to see if the knock values change much with different plugs.

Or maybe I had a retard moment and filled the car with 91?