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Grant Baker

Knock Setup on G4+ Plug in - EVO 6

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Hi Guys,

I've never used the closed loop knock control on a Link G4+ before...

Got a sensor from Link, so have a few questions:

1) Is the sensor a 5v and signal or Earth and signal?

2) Any suggested settings to start with?

If anybody has a pcl file with knock enabled on an EVO Plug in board that they would like to share I would appreciate it :)

Thanks in advance.,

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The sensor goes Earth and Signal, (to the knock sensor wire, not analog input etc) because the knock sensor generates a voltage when a vibration is applied to it.

You'll want to set it to 4-10khz wideband because your engine's bore will have a knock frequency in the ~6khz range.

Realistically you'd want to get this setup for your individual motor, rather than from some base settings.
As each motor has a different background noise level, for example valvetrain noise.
And how tightly you torque down the knock sensor can affect the readings as well.
Will take an afternoon of mucking around but good fun.

I'm setting it up on my car at the moment, not an evo but can give some more detailed instructions if need be.

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Okay so there are a few stages to setting it up.

 

 

1. Wiring
Run one wire to the knock1 or knock2 wire on the link loom, and one to sensor earth, polarity unimportant. must must must must use shielded wire. The knock sensor outputs a very low voltage signal that's prone to interference.

2. Initial settings

Since you are using the 'wideband' knock sensor and an engine with an ~86mm bore has a knock frequency in the ~6khz range select your Freq Channel as 4-10khz Wide Band.

Set Ignition Retard limit to 0 degrees.

Set the RPM high and low lockouts however you like. (500rpm likely not ideal for the low setting)

ikwn5vs3.yf0.jpg

 


3. Cylinder balancing
Your knock sensor is mounted closer to one cylinder than the others. It picks up vibrations, so the vibrations from that one cylinder will give a stronger signal than the others.
So what you need to do, is hold the motor at say 4000rpm (no load) and check the signal strength of each cylinder.
You can check the signal strength by pressing F12 to get to the runtime values screen and looking at these numbers, knock level cyl 1/2/34

5dsdvpi2.ir1.jpg

 

 

See how in that example above, the numbers are 235 / 160 / 255 /145. You need to get these numbers as balanced / equal as possible.

You can adjust the values up or down by tweaking the numbers up and down in Knock control > Cyl setup > Cyl 1/2/34 knk level gain

 

gdwnxrfe.zkv.jpg

 

 

Best to start with a value of 1 for the cylinder that's closest to the knock sensor, and increase the other values to suit. If one of the values reaches '2' (maximum) you can reduce some of the other numbers to less than 1.

4. Non knock noise levels
Since the knock sensor picks up vibrations, there are of course vibrations happening even when there's no knock. As RPM increases, the amount of 'natural' background noise increases too.

The ECU can tell that knock is happening, because there's an unexpected large spike in the 'noise' from the motor around the time of the iginition event. Soooo, you need to find out what the background noise level is for your engine.

According to the manual, a 2 row table with full throttle and 0 throttle is sufficient but this is up to you and how long you want to spend on it haha.

So head to Knock control > Knock target, right click on the table and select Axis setup to define your table similar to this (if you want)

 

nqtlbayt.rbo.jpg

 

Then you need to run a datalog through the rpm range at full throttle to see what the values are for this table. (and coast back down off throttle for the zero TP target, although I'm guessing not much knock happens at 0% throttle)

Open the datalog and bring up a screen to show engine rpm and the knock level global.

Knock level global has a maximum value of '1000'. If you find that you are hitting 1000, you need to reduce the Gain Channel number on the main knock sensing setup page to something a bit lower and try again. Remember that the '1000' has to be the maximum even including allowance for knock which is much stronger signal than the background noise so you need to allow headroom for that too.

 

pdd2lhir.25d.jpg

 

Once you've established these background noise levels for the motor in your table, increase all of the numbers in the table by 20% to give it a bit of a margin against picking up normal engine noise as knock.

At this point, because you've set the maximum ignition retard to 0 degrees in your first step, the ECU isnt taking any action against knock.

Now that you've got everything setup though (unless I've missed a step here, haha) you can turn the knock sensing on by setting an ignition retard limit here, to say 3 degrees or 5 degrees or whatever you want:

eiwsee5f.qcc.jpg

Then as per reccomendations from the manual, it's best to test that knock sensing is working under a scenario that minimises risk of damage to your engine.

So you could drive along at low load / low rpm and induce knock by creeping the timing forward until it knocks and you can see from the runtime values table (F12) that it's working.

From here, it should all be working awesomely. (No responsibility taken for blown up motor though! This is just what has worked for me)

Hopefully it all makes sense though
Where are you based / what is the car used for? 
Keen to hear how you get on.

Edited by Davidv

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Interesting, does narrowing the 'window' help at all with high rpm knock sensing?

I was hoping for a bit of a safety net in the high rpm range.

How do motorbikes etc deal with knock sensing when they're pulling zillions of revs?

Or do they just not bother.

Edited by Davidv

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Hi David,

Most powersport applications do not run knock detection, this is because a knock sensor has difficulty differentiating between the mechanical noise from 2 stroke engine and actual knock. 

Depending on your ignition system type (direct spark being best) and the mechanical noise your engine makes, narrowing the window will allow you to increase the maximum engine speed you can detect knock at.

PCLink help has a little info on this, including a table. Take a look at:

PCLink Help > G4+ ECU Tuning Functions > Knock Control > Knock Control Settings  and then look at the window length section.

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Hi Davidv,

I am just suggesting what I do in alot of my applications, solid lifters, forged pistons etc.

You can go to 8000 rpm if you wish, however I would much prefer to use audible det gear and trust the human ear via electronics and then setup the ignition timing from there.

Regards

Dave.

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The sensor goes Earth and Signal, (to the knock sensor wire, not analog input etc) because the knock sensor generates a voltage when a vibration is applied to it.

You'll want to set it to 4-10khz wideband because your engine's bore will have a knock frequency in the ~6khz range.

Realistically you'd want to get this setup for your individual motor, rather than from some base settings.
As each motor has a different background noise level, for example valvetrain noise.
And how tightly you torque down the knock sensor can affect the readings as well.
Will take an afternoon of mucking around but good fun.

I'm setting it up on my car at the moment, not an evo but can give some more detailed instructions if need be.

If I'm using the stock evo knock sensor and 86mm      Bore as well. Should be be using the same 4-10khz frequency ?  

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