Factory PCM knock control discussion
 

There's a general sentiment around here that says the factory knock sensor, for all practical purposes, does nothing. But do we just not understand it? I have a log here of a WOT pull on an Rx-8 with a Greddy kit and an Emanage. It was originally posted in my thread about how the Emanage default timing maps suck.

https://www.rx8club.com/attachment.p...1&d=1276031154

This appears to be knock retard, especially since the owner reported a hesitation here. The EMU is reporting rediculously low timing advance values. Those two little dips are on the leading but then the trailing remains flat until the engine comes off throttle. I don't know if that means the spark was cut completely on the trailing or what. One thing to notice here is that the retard on the leading happened extremely fast (about .02 seconds), if the Emanage logger is to be trusted. It may not be possible to see this on an AP or other logger.

The sample rate for the Emanage Ultimate logger appears to be much higher than what direct PCM interfaces (AP etc) are capable of, approximately 50 samples per second. This is because the EMU logs sensors directly instead of going by what the PCM reports, which of course also has its disadvantages.

Here is another log of what appears to be detonation and knock retard:

https://www.rx8club.com/attachment.p...1&d=1277939537

5500 rpm on this log too. Boost is about 5.5psi, leading timing was 27 degrees with 15 degrees split until the knock occurs. The leading timing retards suddenly and recovers, but the trailing appears to be retarded or cut completely until the throttle closes.

So does anybody have any logs showing knock retard? The questions I wonder are:

1) Does the Rx-8 PCM have some kind of long term knock control strategy like so many other manufacturers have? It may exist and we just don't understand it.

2) Is there some kind of filtering or noise baseline calculated by the PCM? On certain Evo applications you can actually change this logic to affect the sensitivity of the knock control

3) In the AP helpfile I have (I don't have an Rx-8 AP) it lists a "Knock Retard - Base" table but with no description. Anybody have a screenshot of it?

4) There are timing decrement tables listed in the AP, to specify how many degrees of timing are pulled per knock event. But in the logs I've shown above the timing appears to be pulled very quickly and very drastically. I wonder when those decrement tables are actually used and how a knock event is actually determined.

This again makes me wonder if there are more than one knock control strategies that we don't really understand.

Max retard is -10 degrees....those logs look suspiciously like ignition dropout...not knock retard

AP has 10 tables for knock control

Base table...-10 below 5KRPM
Gear specific tables 1-2 and 3-4 -1degree decrements Gear 5-6 -2.5 deg decrements

MAX rpm 7000rpm
Min ECT 50 degrees

did you solve this issue?
was it a bad knock sensor?
actual detonation?

or some odd ignition issue?

I seem to be having the same issue, I was finally able to log the event, but its basically standing on the throttle 5900rpms and stays there, my logs show the leading pulling timing
about 5psi, too, after releasing the throttle the car goes back to normal

I can cruise in same gear at 6500rpms no problems.

Yes this is a thread revival, but its better then starting a new one

are you sure? This can be caused by other engine load conditions like air intake temp etc, nobody I know of has actually seen it work, the Cobb will supposedly read it directly but always shows zero change

I dont know if I want to log it again to see. Intake temps are pretty steady 2nd gear is 59 and drops to 49, random timing pull. 3rd gear is 43 - 41, strong pull in one sec it pulls from 11 down to 5 degrees. Stock o2 is pegged 10.95, auxwo2 (in catless midepipe) reads 11.9 - 11.6.
So real knock or?

Looking at logs again. Car has to be at 50% load before knock senser can work (atr setting) right past 50% load on my logs timing starts getting pulled and messed with

The AP will specifically log knock retard. There is no need to guess.

I made some adjustments to my tune (Knock section). when weather permits I should be able to make some more logs, with my quick preliminary run, and some sliding in ice there didn't seem to be any knock sensor detection to pull timing

did you have knock before? If you did you never stated so.


.

Did I have physical detonation or knock? I don't think so, never heard any, never any "jerking", nothing in the logs suggested I did.

However

Did the knock senor detect "something" and pull timing? yes

Did you see this as a change in timing or an actual knock retard value?
If it is only the former, than the knock sensor had nothing to do with it.

It is likely that you have bad IAT values being reported sporadically.

Is that your guess or did you actually go back and specifically log knock retard using the AP function as was previously discussed? Again, if you did it was never stated.


https://www.rx8club.com/attachment.p...1&d=1324197547

I was able to take some logs today its pretty cold 34-36 degree intake temps.
knock senser never activated
Timing was being pulled....

how does intake temps affect timing?

rpm Time auxafr oemwot
6461 0 5 0 11.25 10.95
6595 0 5.5 0 11.39 10.95

looks like its starts preparing for the apv? is there a timing retard for apv on cold intake temps?


5583 0 11
5742 0 8.5
5910 0 8.5
6041 0 9
6193 0 9
6193 0 9
6338 0 7
6461 0 5
6595 0 5.5
6786 0 7
6906 0 10

I haven't experienced this issue, but sounds to me like it may be pulling timing due to a high RPM delta. How do you have those tables set?

AFAIK, intake air temperatures only affect timing by changing load.

I don't see a High RPM delta, do you have another name?

there is Leading rpm delta A & B, and Trailing RPM delta A & B. both of which have not been changed from Stock

Actually those are the ones I'm referring to. As RPM changes quickly, these tables may come into play, though for my car I only really see it at idle and going off throttle.

I don't really know how to adjust these tables properly, and I wonder if there isn't something wrong with how they are set up in ATR. For example, if I use the Mazda scaling, the values come out like this:
https://www.rx8club.com/attachment.p...1&d=1324270431

Versus this in ATR:
https://www.rx8club.com/attachment.p...1&d=1324270431

are you saying that my rpms are climbing so fast that these tables are reducing timing?

I have heard that this is possible.

so the question is, now that I am forced induction should I leave it alone or change it?

wouldn't that show up in the logs, its a steady 36 degrees, then 34 degrees. and it seems to be happening in a predictable fashion

You heard? lol

Was I really being that vague?

Sometimes you have to wonder why you even bother ...

.

https://www.rx8club.com/series-i-engine-tuning-forum-63/timing-fuel-more-boost-191027/#post3427930 Interesting thread with more hints

https://www.rx8club.com/showpost.php...&postcount=138 obviously my issue

https://www.rx8club.com/showpost.php...70&postcount=9. yet again

the key search phrase was "rpm delta"

thanks oltmann,

now onto further investigations.....

:bowdown:

Anyhow, I'm reasonably convinced that this table is screwed up in ATR. If you want zero timing retard, enter -64. If you want advance, add desired advance to -64. If you want retard, just enter the value. 32 degrees in either direction is the max.

I think that the A tables are for when the car is in gear, and the B tables are for neutral, but I haven't checked yet.