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Subaru Knock sensor setup

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Hi guys!

 

Any help please with the knock sensor setup for the Subaru ( 2002 WRX STI )

A very nice link for the EVO setup was found, I want the same for the Subaru please. The below link was a fantastic help file for the EVO knock sensor setup, hopefully there is just a nice one for the Subaru ?

 

 

 

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The information I have says that the WRX V7 onwards uses a narrowband knock sensor with a frequency on 13kHz. If you use a 'donut' style (wideband) knock sensor you will likely want to use a 6 or 7 kHz frequency filter. A lot of what was discussed in the forum thread you linked to is applicable to your subaru. The numbers you use may differ, but the principal of setting up the knock control system is the same.

Scott

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The information I have says that the WRX V7 onwards uses a narrowband knock sensor with a frequency on 13kHz. If you use a 'donut' style (wideband) knock sensor you will likely want to use a 6 or 7 kHz frequency filter. A lot of what was discussed in the forum thread you linked to is applicable to your subaru. The numbers you use may differ, but the principal of setting up the knock control system is the same.

Scott

Hi Scott !

I use the standard Subaru knock sensor, which is a round shape yes. I have set it to 6mHz and gain of 40. It works no problem, I am just unsure if it is correct?

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I expect this is not correct. The gain level I have seen used is normally 1 or 2.

Try setting the gain to 1, then set the frequency filter to 13 kHz. Open the runtime value window and look at the left hand column of the knock tab.  Hold the engine speed and load at a certain point and make note of the values you get for the individual cylinder levels. Now let the car return to idle and set the frequency filter to 7 kHz and repeat the test. Which filter gives you higher values for the individual cylinder trims?

Scott

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I expect this is not correct. The gain level I have seen used is normally 1 or 2.

Try setting the gain to 1, then set the frequency filter to 13 kHz. Open the runtime value window and look at the left hand column of the knock tab.  Hold the engine speed and load at a certain point and make note of the values you get for the individual cylinder levels. Now let the car return to idle and set the frequency filter to 7 kHz and repeat the test. Which filter gives you higher values for the individual cylinder trims?

Scott

I will test and confirm, attached my current settings

scooby-knock-settings.jpg

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Hi

I made the changes you requested, from 6kHz to 13kHz and gain from 40 to one.

YOur settings are much "better", since it now looks more like true knock if you know what I mean. On idle, with my 6kHz setting, the knock bar was allready active, which I though were very strange, but since it was my first time with the link ecu, I ignored it.

Now with your 13kHz and 1 gain setting, on idle the knock bar is 0 and normal, only when revving and putting load does the knock happen like normal, more on cylinder 3than the rest etc.

 

 

knock output-6kHz-40gain.jpg

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The knock sensor will normally produce a level reading that increases with engine speed and load, even if knock is not occurring. What you need to do is set the values in your Knock Target table to be about 10% higher than the values you typically see at each engine speed and load point. Then whenever an individual cylinders level exceeds the target level the ECU will start to retard that cylinders ignition timing.

Scott

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Hi Scott!

Your replied are always very much valued by me, helps me so much !

Ok, so please explain this one quick, to make sure I get it right going forward, as I am definitely moving all customer cars to link ecu, fantastic !!

This car's Knock target table has 0 values everywhere (by default). SO please explain a bit what you meant, to make sure I do it correct. SO right now the car knocks and it shows it via the knock sensor, but because I have no values here, it is not retarding timing etc ? Sorry, two questions there :) 

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Ok, here (quickly) are the steps you would normally take to set up the Knock detection system:

  1. Make sure the ignition system is completely tuned.
  2. Set the knock gain to a value of 1.
  3. Select the correct frequency filter (we have covered this)
  4. Monitor the individual cylinder knock levels, adjust the gain until the max reading you get in the levels is approx 500. This is normally somewhere around high rpm and high engine load.
  5. Monitor the individual cylinder knock levels and adjust each cylinders gain until the cylinders all read evenly.
  6. Fill in each cell of the target table. Set the values to be 10% higher than the values you are seeing on the individual cylinder knock levels. Logging could be a helpful way to do this.

Now whenever the knock level of a cylinder exceeds the current value from the knock target table, the ECU will try to retard the ignition timing for that cylinder to reduce the noise (knock) level. You can decide at what rate the ECU will retard the timing, and what the maximum level of retard can be. Benefits to having a quick retard and large maximum retard are engine protection. Benefits to having a slower retard and small maximum retard are the engine does not drop so much power.

Lets assume you have ended up with a setup like this:

Knock_setup.thumb.PNG.cbf08394376e88db9d

At 50% throttle and 1500 RPM you are normally getting cylinder knock levels of 255, so you set the cell in the Knock Target table to 280. One day you lend the car to someone and they put a lower octane fuel into the tank. This causes the engine to knock lightly and produce cylinder knock levels of 320. The ECU sees this and retards the ignition timing until all affected cylinders (probably all of them) have a noise level less than 280 or until the Ign Retard Limit is reached.

Regardless of the cause of the higher cylinder knock levels the ECU will retard the timing in an attempt to reduce the levels to be below the level specified in the Knock Target Table.

One good way to view this is by logging on the Timeplot. Display each cylinders level and then then Knock target (threshold). This will allow you to easily see when a cylinder jumps up over the allowable level.

Scott

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Great info here - this will help me setup up my car in the next few weeks! :)

Can I use 2 X OEM subaru knock sensors into the Link - this way Im covering the LHS and RHS banks.  Is more better? :)

Cheers.

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The OEM ecu header only has 1 knock pin.  So you can only connect one sensor.

Correct - Im wiring in a Fury ecu - I should've mentioned that I suppose. :)

I have a spare knock sensor - so was wondering if its benefical to run two?

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Yes using two knock sensors on a boxer engine should enable you to achieve a better s/n ratio provided there are suitable mounting locations on each bank somewhere near the top of cylinders.  Having said that in my experience on the few subarus I have tuned the knock control was effective and reliable with just the stock knock sensor location.

 

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Ive got a 97wrx v3/4 ecu, ive set my frequency to 6khz and with 2 gain channel, when logging i only see cylinder knock levels around 10-60.

When i set gain channel to 40 im getting cylinder knock level of 10-20 at idle and 60 when shutting off throttle from 30% at 3000rpm

Im trying to do the steps as scott posted but im way off. Any ideas if what im doing wrong? 

Please help 

Thank you.

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