knock retard

[DaleNixon]

"False knock is characterized by a sharp spike to an immediately high value of KR followed instantly by the KR Recovery Rate. It doesn't grow with engine RPM or load, it jumps to a high value on throttle input and then recovers to a low value, or zero perhaps, as engine RPM continues to increase. Note that this is exactly opposite to the characterization of REAL KR. Remember, knock is simply specific noise detected by engine microphones. Because it happens to fall with in the frequency of real KR does not necessarily mean that it IS real KR."

Sounds like what I get occasionally when cruising.

 

[Bravnik]

i usually only get random knock when my boost air temps are above about 110+ and i have a FMIC. that doesn't mean its doing its just because in reality it has nothing to do with when you are cruising since that air won't cool as much as boosted air. whenever i get into boost it does drop quickly though so its doing its job. the problem is our intake manifolds seem to heat up quickly from the engine and basically act like an oven for the air coming in.

I can see that happening as well. Goes with the TON of theories out there. I even read in one post that the LSD on one model of Pontiac can cause a high KR reading under normal driving conditions.

Hopefully the AP Race Tune will allow us to adjust the KR sensor under varying driving conditions like some other cars tuners do. This would allow us to set a higher number for Idle, Cruise and Low Throttle applications and keep the stock KR setting for WOT.

We can hope.

 

[bova80]

that is a good read and that is exactly how my random knock happens too. one time instead of letting off the throttle immediately i just let it go and it fell back down to zero and i never felt a difference in performance.

 

[phantom6294]

Conditions change all the time in normal cruise. The ECU is programmed to pull timing for actual KR and also to anticipate possible KR situations. That is why you can be cruising just fine and go up a little hill (like an overpass) and have to give a little more gas to maintain speed and all of a sudden you see 2KR. You're not getting actual pre or det, but the PCM is adjusting due to load and maybe your timing was more aggressive for the current condition. Thus is pulled a little timing and re-adjusted. This is what I meant by my timing statement above.

Once again... couldn't disagree more. It makes zero sense for the ECU to programmed for a certain timing map for certain operating conditions and simultaneously be programmed to retard timing... 'just in case' under different operating conditions. Why not just have less timing to begin with??? It's like saying an ECU programmer spent all this time determining the optimal timing curve for different operating parameters... and then said, 'you know what... if these other different parameters occur, I'll just use KR to retard the timing.' Makes absolutely zero sense. The ECU determines the spark timing needed taking info on its various inputs (sensors) a calculated load then does a look-up in a timing table(s) and sets that timing. Unless it gets a signal from the knock sensor, it is going to stick with what is in the map.

In your example, when you start going up that hill, the load calculation will change, the ECU may (or may not) change the timing based on the new calculation. It certainly isn't going to go... 'hmmm... the load has changed, I'll retard the timing just in case....' If the load has changed enough, it would be using a different part of the timing map. Of course, generally speaking, increasingly the load would probably correspond to lower the spark advance any ways, as less timing is needed the denser the fuel/air mixture is, but using KR for such a situation is ridiculous.

What your DH logged is what is called False KR. KR is when the KR starts and continues to build. False KR is usually a quick spike followed by an immediate decline to a lower number or zero which is the exact opposite of what true KR looks like in a log.

There is no such thing as false KR. If the ECU is reporting KR... it's KR... plain and simple; when the ECU is reporting KR it is retarding the timing. While I concede it is within the realm of possibility that any particular KR event may be false knock, a spike and then decay of KR does not guarantee a false knock reading. Assume for a moment that in my log it was an actual instance of knock. The whole point of a knock sensor and KR is to detect knock and then remedy the problem. How do you remedy the problem? You retard the timing. For whatever reason the initial knock occurred, retarding the timing eliminated the conditions under which it occurred. It isn't a hard concept... the ECU detects knocks it retards the timing. If the timing is retarded enough, it should eliminate the knock. It would then only make sense to attempt to return to the normal timing map (which, in theory is the 'optimal' timing for the given operating conditions, though optimal may be emissions/mileage optimal).

Here is a quick down and dirty explanation of KR.

https://www.zzperformance.com/grand_...les1.php?id=20

Problem is... the author either glosses over, or doesn't understand the difference between Pre-ignition and detonation -- two very different beast with two very different causes and two very different results.

Here's a much better reading on pre-ignition, detonation and spark timing...
http://www.streetrodstuff.com/Articles/Engine/Detonation/index.php

 

[bova80]

ok so i talked to christian from cobb about this and he said that is a good article but it isn't how the mazdaspeed ecu works. he also said that with the ATR software you won't be able to change the sensitivity of the sensor as this sensor is calibrated very well.

 

[RC08MS3]

haha, id love to see you guys argue about phantom knock, ever think maybe thats what cruising KR is?

 

[Bravnik]

Once again... couldn't disagree more. It makes zero sense for the ECU to programmed for a certain timing map for certain operating conditions and simultaneously be programmed to retard timing... 'just in case' under different operating conditions. Why not just have less timing to begin with??? It's like saying an ECU programmer spent all this time determining the optimal timing curve for different operating parameters... and then said, 'you know what... if these other different parameters occur, I'll just use KR to retard the timing.' Makes absolutely zero sense. The ECU determines the spark timing needed taking info on its various inputs (sensors) a calculated load then does a look-up in a timing table(s) and sets that timing. Unless it gets a signal from the knock sensor, it is going to stick with what is in the map.

In your example, when you start going up that hill, the load calculation will change, the ECU may (or may not) change the timing based on the new calculation. It certainly isn't going to go... 'hmmm... the load has changed, I'll retard the timing just in case....' If the load has changed enough, it would be using a different part of the timing map. Of course, generally speaking, increasingly the load would probably correspond to lower the spark advance any ways, as less timing is needed the denser the fuel/air mixture is, but using KR for such a situation is ridiculous.



There is no such thing as false KR. If the ECU is reporting KR... it's KR... plain and simple; when the ECU is reporting KR it is retarding the timing. While I concede it is within the realm of possibility that any particular KR event may be false knock, a spike and then decay of KR does not guarantee a false knock reading. Assume for a moment that in my log it was an actual instance of knock. The whole point of a knock sensor and KR is to detect knock and then remedy the problem. How do you remedy the problem? You retard the timing. For whatever reason the initial knock occurred, retarding the timing eliminated the conditions under which it occurred. It isn't a hard concept... the ECU detects knocks it retards the timing. If the timing is retarded enough, it should eliminate the knock. It would then only make sense to attempt to return to the normal timing map (which, in theory is the 'optimal' timing for the given operating conditions, though optimal may be emissions/mileage optimal).



Problem is... the author either glosses over, or doesn't understand the difference between Pre-ignition and detonation -- two very different beast with two very different causes and two very different results.

Here's a much better reading on pre-ignition, detonation and spark timing...
http://www.streetrodstuff.com/Articles/Engine/Detonation/index.php

No such thing as False KR? Are you serious? Over sensitive KR sensors and False KR readings have been apart of Tuning from the day the KR sensor was designed.

Anyway, I have my theory, you have yours. To each their own.

 

[phantom6294]

No such thing as False KR? Are you serious? Over sensitive KR sensors and False KR readings have been apart of Tuning from the day the KR sensor was designed.

Seriously, did you even bother to read my post?

While I concede it is within the realm of possibility that any particular KR event may be false knock

The problem is people, like you, who misuse terminology confusing everyone else.

KR = Knock Retard --> A value by which the ECU has retarded the timing in response to a detection of knock.

Knock = Detonation --> "The spontaneous combustion of the end-gas (remaining fuel/air mixture) in the chamber."

You can have a false detection of knock. Yet, claiming that the Knock Retard is 'false' is just plain ignorant. If the ECU reports a KR value, it's pulling timing, plain and simple; there is nothing 'false' about it.

 

[Bravnik]

Oh I'm sorry Mr Literal. If you could not understand my point then I'm very sorry.

I never meant to imply KR was FALSE as yes you are getting your timing pulled. I thought that was pretty clear and common sense. Maybe I give forum members credit for common sense more then I should.

So let me be more literal in my description. The KR you are getting under normal driving conditions is not actual KR due to knock, detonation or pre-detonation it is due to other reasons not yet determined but considered normal except under WOT conditions. Call it phantom knock if you will.

I think it is due to your car's ECU setting the thresholds too high (or low) and the ECU is programed for to determine pre-knock conditions and adjusts accordingly BEFORE the knock occurs as a preventive measure. But that's just my theory and it may or may not be right as I'm not a Mechanical Engineer nor am I a ECU programmer/Electrical Engineer. Again, to each their own and there are a TON of theories out there for why cars see KNOCK under normal driving conditions and get minor KR due to it.

Is that clear enough for you?

The end point I was TRYING to make is that KR (YES KNOCK RETARD) under normal driving conditions is NORMAL and nothing to worry yourself over (Unless you hear Pinging). KR under heavy load (WOT) is dangerous. Those without a DH or other device that can see KR will never know they even have KR under normal driving conditions.

 

[phantom6294]

Oh I'm sorry Mr Literal. If you could not understand my point then I'm very sorry.

I never meant to imply KR was FALSE as yes you are getting your timing pulled. I thought that was pretty clear and common sense. Maybe I give forum members credit for common sense then I should.

So let me be more literal in my description. The KR you are getting under normal driving conditions is not actual KR due to knock, detonation or pre-detonation it is due to other reasons not yet determined but considered normal except under WOT conditions. Call it phantom knock if you will.

I think it is due to your car's ECU setting the thresholds too high (or low) and the ECU is programed for to determine pre-knock conditions and adjusts accordingly BEFORE the knock occurs as a preventive measure. But that's just my theory and it may or may not be right as I'm not a Mechanical Engineer nor am I a ECU programmer/Electrical Engineer. Again, to each their own and there are a TON of theories out there for why cars see KNOCK under normal driving conditions and get minor KR due to it.

Is that clear enough for you?

Nope... because pre-detonation is another poor term -- pre-ignition is the correct term, which a knock sensor generally cannot detect. The knock sensor is looking for that 'pinging' of the cylinder block caused by the sudden spike in clyinder pressure when detonation occurs. Pre-ignition happens very early in the combustion stroke and there is no spike in cylinder pressure, but rather a slow (comparitvely speaking) rise to insane cylinder pressures.

I disagree with the blanket statement that the detection of knock under light load conditions in the 3-4k RPM range is a false detection. Is it possible? Sure. Can anyone prove one way or another? Unless we add a glass viewing portal to the combustion chamber and visually inspect each combustion event while cruising... we probably won't know for sure. Yet, your idea that the detection of knock is false is based on what? I realize that an engine moving at 3-4k RPM has a lot of things moving around that might set off an overly sensitive knock sensor. Yet, light load conditions between 3-4k RPM also requires a significant amount of spark advance for proper combution. Further, this range is a common range for our cars to cruise in... it seems quite plausible that Mazda was a bit aggressive with the spark timing under these operating conditions for purposely of fuel economy and/or emissions. Further, it seems plausible that if it were some kind of 'background' noise being picked up, that KR would be more frequent than it already is.

I take issue with the idea of telling people, as a blanket statement, it's false knock... nothing to worry about. It may in fact be a false detection... but what if its not? Well, as I've said, it can probably be ignored if it while cruising under relatively light loads. If the KR value jumps but then decays, and it was in fact an occurence of knock, it was a very short instance and the car is returning to normal. If the KR value is sustained or continues to jump back up, it is probably a good idea to ease off the throttle.

Furthermore, I think the idea that the ECU attempts to "pre-empt" knock is just asinine -- it makes absolutely zero sense. There is no way for an ECU to 'sense' a pre-knock condition. Pray tell... what are the pre-conditions for knock? Well, I'll theorize... it could be the engine overheating... well, engine temps are normally taken into account in engine load calculations and thus, timing calculations. It might be a lean AFR condition... well, the computer then uses the fuel trims to adjust the fuel being injected. Fundamentally, if the engine isn't knocking... there is ZERO reason to retard the timing. Retarding the timing, for no reason is going to cause a loss of power, increased emissions and unburnt hydrocarbons. Why on earth would Mazda surely spend countless hours developing a timing map, to then turn around a program the ECU to completely ignore that map? That's the whole point to the knock sensor... run the timing maps as programmed... and when/if something happens (the knock sensor goes off) then pull timing accordingly.

 

[Alexsered]

I can see that happening as well. Goes with the TON of theories out there. I even read in one post that the LSD on one model of Pontiac can cause a high KR reading under normal driving conditions.

Hopefully the AP Race Tune will allow us to adjust the KR sensor under varying driving conditions like some other cars tuners do. This would allow us to set a higher number for Idle, Cruise and Low Throttle applications and keep the stock KR setting for WOT.

We can hope.

you know whats weird about what you just said, when I'm going around a big turn like the exit, I get knock at almost any RPM, but only when I'm trying to boost. I always thought that was weird, maybe an LSD issue?

 

[CHICO2003]

This reminds me of when I took my little cousin trick-or-treating. He turned around after pushing the doorbell and sad he thought it was broken. So I said...