EMS

The ECU isnīt able to "detect" knock between all other engine noises at high revs. Therefore the knock correction is switched off above 5.000 - 5.500 RPM. So donīt be fooled (like me, as I start monitoring knock correction) and monitor knock correction only until 5.000 RPM! (I had some SERIOUS knock as I was advancing the ignition and waiting for some negative knock correction! )

Mark.

[Edited by EMS - 9/5/2002 10:18:22 AM]

Bob Rawle

The factory ecu detects "knock" at all rpm's, the compensation maps, however, are not set to react everywhere, certainly though the new age cars, running off the knock sensor as they do, detect the knock sesnor output and react to it at all times.

There doesn't have to be det (real that is) for the ecu to react with "knock" correction.

Link knock detection is active across the whole map(s)

cheers

Bob

[Edited by Bob Rawle - 9/5/2002 9:47:50 PM]

Razor2001

Lets try and simplify please:

Is the below true or false ?

If my engine knocks (regardless of what rpm etc etc) a LINK Knock Link will detect it by lighting the indicated knock warning lights ?

The STI-7 knock correction will correct any dangerous levels of knock period (again regardless of what rpm etc etc)?

Experts please advise

Cheers,
Ray



[Edited by Razor2001 - 9/5/2002 10:11:30 PM]

BruceWarne

Give it to me straight:
Can I believe the "knock" signal in DD?
If DD says knock has been detected/not-detected can I believe that?

Thanks


[Edited by BruceWarne - 9/6/2002 10:05:27 AM]

BruceWarne

What is the DD sampling frequency? 10HZ (100ms)...

What is a "knock"'s frequency?

What is the OE ECU's sampling frequency?

I reckon at high RPM a solitary knock can get missed by the DD...but if the ECU samples and reacts fast enough, it can "cure" that knock before the next DD sample...

7000 rpm is an engine frequency of about 116 HZ.

But a cylinder only "fires" every second stroke...58HZ...(once every 17ms)

Gees, the DD can miss a number of knocks/strokes between samples...


[Edited by BruceWarne - 9/6/2002 10:51:03 AM]

john banks

KILO Hz though... that doesn't mean that it will only last 1/6000th of a second though just the frequency of the noise of course.

http://home.netcom.com/~bsundahl/kno...nockSounds.htm has some knock on another engine.

You would hope that in each timeslice for the serial port the ECU reports the worst case knock during that time but we just don't know. Running at 20 MHz and likely using DSPs should mean it is quick enough?

[Edited by john banks - 9/6/2002 12:09:44 PM]

EMS

Richard,

as Bob also said, the new age ECUīs permanently are "searching" for the optimum timing. I saw both the STi7 and WRX do use quite a lot of positive knock correction under normal circumstances. So if the car is detting, you still can see positive knock correction. (e.g. +2 deg in stead of +8 deg without knock) A DD measurement in 5th gear (from 2.500 - 7.500 RPM) at a standard STi7 gave me knock correction between +11.5 and +2.0 deg (!) I saw the knock correction value changing until 6.900 RPM. I donīt know exactly how this correction has been setup in the ECU, because I could produce some serious knock by rising the boost!

You canīt compare these with the "older" ECUīs which has a different setup of the knock correction. (hardly any possitive knock correction and negative knock correction when knock is "detected") I think a Knock Link is a nice tool when mapping a car. (every little knock spike is visible)

John,

I never did see any knock correction above 5.500 RPM with the MY99 and MY00. I tried realy hard by advancing the ignition until the engine was sounding like a diesel (my own car)

Mark.

[Edited by EMS - 9/6/2002 7:22:00 PM]

Razor2001

Hi Guys,

Just out of curiousity would a DeltaDash show actuall knock in real time similar to the lights on the KnockLink only in more detail as it shows actual nummerical values ?

Just was curious if I decided to go for a nice long 1/2 - 1 hour run in multiple conditions, multiple speeds, etc etc if I could essentially see what a KnockLink sees only in more detail ?

I realize that the KnockLink is more pratical for dialy usage becuase you don't have to hook up a computer to your car and drive around; however, just wanted to confirm that I can tell how much knock is present if any.

Thank you,
Ray

Reason for asking is should be going for a deltadash run this weekend

john banks

It doesn't show it you like the Knocklink. On most cars the Delta Dash information would be enough - you are seeing the knock correction. However, the ECU seems to ignore some types of detonation which you can see on the knocklink. Both would be ideal if you are tuning the car.

Razor2001

Awwww man....that is not the answer I was looking for John

Thanks for reply though. So I guess I should be looking at the knock correction and if it is ever more than -.03 or so then that means car is knocking too much ?

Thanks again,
Ray

john banks

An STi 7 usually runs positive knock correction - say 7 or 8 degrees. If there areas in the rev range where this dips particularly severely (like to zero or negative) this may need attention.

Sorry m8 my replies are not particularly encouraging regarding your car. I'd just rather it stays in one piece for you

Razor2001

I appreciate the honesty, as you say I want to keep my car in one piece as well

Cheers,
Ray

rroberrto

Hi,

Been logging several high speed runs (up to 140 mph) and DeltaDash gave mixed results for "knock signal" and its relationship with knock correction.

Only very rarely does the knock signal turns to 1, but knock correction seems to work at all time at high load/rpm zones regardless of the value of KnockSignal. During similar runs under similar conditions, the correction can vary from -0.5 to -2.5 at similar boost/rpm points. Since i reset the ecu before each run these varying correction must be based on some on-the-fly knock signal rather than "learned" knock correction. If above reasoning stands true, then there must be another knock parameter that deltadash hasn't got hold of that the ecu uses to come up with the appropriate timing correction. And it must not be boolean like the deltadash's "knock signal"

So where does that leave the boolean knock signal? is it of any true use? what's even more interesting is that during my last run the knock signal turned on at some point around 120 mph (4th, 6300 rpm, 14.1psi, lambda 0.925v) but no knock correction whatsoever!!!

Any ideas anyone? I'm truly puzzled.

Robert

Scotsman

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The Bahamas, Scotland and Taiwan.

john banks

Robert, I am not at the bottom of it by any means. The knock signal hardly ever comes on on my car. I had the same as you when it did though - no correlation with correction. Ecutek have not yet unlocked the mysteries of the knock correction algorithms unfortunately (busy cracking the 01/02).

Razor2001

So deltadash will not give me any idea if I am doing any harm to my engine running it the way it is ?

What are the key things I should look for to get an idea if my car is running in a safe zone ?

Cheers,
Ray

john banks

Yes DD will, but the knocklink will give you other info.

dowser

What MY are we talking about? I was DD'ing a decatted, bleed-valved STi7 on the rollers a while back. At around 7k rpm the (digital) knock signal sensor went to 1...the analogue knock correction kept on applying 5 degrees of advance

Road operator reckoned he may have heard det - I heard nothing, but would have loved a knocklink for confirmation!

As per John, I'd prefer both + AFR montoring.

Richard

Richard

rroberrto

Thanks John, glad to know I' not the only one afflicted. But still, the on/off knock signal doesn't seem to make any sense or be of an use, or does it?

Mark, Gee, thanks for the tip of why no correction being made above 5500. I've observed this phenomenon too, and being naive i thought since ecu is dumping more than enough fuel the knock had somehow gone quiet higher up.

Does switching to colder plugs help control det? Little as it might be?

Robert

dowser

Hi Mark,

I agree it's strange - by why did the digital signal go high? And what is it on the new-age's that tell the ecu it's OK to keep using positive knock correction (advance) above 5k...you'd think if it's disabled it'd just use the map timing?

The STi7 owner ordered a knocklink

Richard

john banks

Mark I have seen knock correction up to 6000 RPM but none with the manifold. I could not run anywhere near as much timing (we are talking 6 degrees or more that you were running) than you at similar boost although the ECU kept quiet. It seems to ignore transition detonation. But I am probably running too much boost for the cooling I have so timing is quite retarded at present until the FMIC goes on.

Razor2001

All confused now ??

So the STi-7 knock sensor can't detect knock above 5,000 rpms ?

Does the LINK KL detect it above 5,000 rpms ?

Will the DD lean/rich measure be as good as the AFR light bulb one sense they both use the 02 sensor on the manifold (on the new STi-7's) ?

Help....Cheers,
Ray

nom

Everything gets a bit noisy above 5-5.5k rpm; most knock-sensors will not give as good information, there's just too much going on to be able to definitively say whether there was knock or not.

The good - and bad - thing about DD is that the information is stored, rather than instant. If you're testing/checking with a knocklink & AFR in front of you, little lights come on & you stop doing whatever it was that made the lights come on . DD, unless someone is sitting there reading numbers off, you only find out later. But you will find out in a lot more detail & be able to cross-reference, compare with old info, etc, so are actually able to trace the problem with some degree of a useful outcome.
Which is why it is good to have both

nom

All seems a bit barmy!
Any particular reason why the ECU wouldn't react to knock in certain ranges? And why does it correct for 'knock' when it doesn't detect it?
Or is stick wrong end complete I am getting?
Or more likely; how far over my head is it? Not even worth trying, I imagine

Bob Rawle

Since the ecu reacts to a level of knock sensor output it will only interpret that ... wether there is knock or not you need to check with det cans ... its the only way. A knocklink can then be correlated against that knowledge and you can then be sure or not about what is being displayed.
How an ecu reacts ie what it does is then down to the software code, its sensitivity and how its designed to run timing. Latest cars run off the sensor real time so they are always correcting against knock output, older ecu's react to a different level and only once its seen do they do anything. If a sesnor output is erroneous it will still react to it, perhaps incorrectly either way.

Aftermarket ecu's which have knock detection can be programmed to react to any level you like.

john banks

The lower reporting frequency could mean it does or does not report the smaller timeslice events? Not sure, good point.

The frequency of knock on our engines I gather is in the range 5-7 KHz.

The knock correction reported by DD is a good guide on the pre-MY01 cars, but when things are tuned to more extremes it can lose the plot and I gather Bob gets it retarding when there is no knock, and mine doesn't retard when there is despite no sensor, loom or ECU problems. Undoubtedly there is much more to the knock control than we are aware of and can adjust at present. All we have been able to alter is the point where x knock correction for y time leads to duty cycle dropping to zero. I got unpredicatable results from adjusting compensation maps.

On the MY01 and after who knows - it is so active on the knock sensor maybe the algorithms are much better and it is more reliable, but there is not enough information yet to say I don't think. Bob?

I suppose one of the beauties of an aftermarket ECU is that things like knock correction are designed from the ground up and you can know the full setup from day 1, whereas the OEM ECU is still a bit of a PITA in this respect. It seems to only **** up when you go a bit mad with your tuning. My approach on my car so far has been to get det free timing in the most horrible conditions I can arrange , and then pull it back a bit more for safety. Doesn't seem to affect the performance too badly, and much better than worrying about it detting.

BruceWarne

5-7 Hz, so the DD should pick it up more often than not...

Razor2001

LOL....I am lost my friends....but from what I can gather, neither DD or a KnockLink will give you 100% confidence that your engine is free from knock !

Oh well, back to the drawing board, I guess some degree of confidence is better than NIL !

Cheers,
Ray

Bob Rawle

Mark thats my point exactly, the ecu does not always recognise knock and sometimes reacts to what is not knock. My car (Sti5) has produced knock correction wherever there is compensation at one time or another .. mostly adds timing at high revs though and only takes out between 4 and 5 k rpm on heavy load. Bottom line, don't rely on the DD knock correction readout ... you need to sense check each car with cans to make sure of what is happening. Once you have done that then DD is a great tool.

Razor2001

Where can we get a hold of these Det Cans ?

Oh yea, what are they and what in the world do we do with them once we have them ? LOL

Cheers,
Ray