Can pulling too much timing cause knock?

[jtrosky]

I'm having KR issues during high-arimass, low-RPM situations (like when trying to accelerate mildly or maintain speed on the highway if there is a slight incline). I've been pulling timing a few degrees at a time to address this KR and now it seems like I'm getting more KR, which made me wonder if pulling too much timing can acutally cause knock?

I've looked at old logs where I had the timing much higher in this area (different tune completely) and I'm just not seeing the KR in those logs - and the timing is twice the amount I have in my current tune for this particular airmass/RPM combination.

Thank you!

[GHuggins]

Someone can correct me if I'm wrong here, but it's always been my understanding that running low timing is worse than high timing on DI platforms? I also know that the knock parameters on these motors are overly sensitive and you could be experiencing a fuel knock instead of a spark knock - just some other things to think about and why lower timing might be worse than higher on these?

[jtrosky]

Thanks for the reply. Very interesting. Well, since the older logs I looked at seem to agree with that you're saying, I'm going to give it a shot and increase them quite a bit over stock. I get the KR with the stock values (and even more when I reduced the values below stock), but I don't seem to get the KR when I loaded a commercial performance tune, which had much higher spark advance values in the area I'm talking about. It's almost like the spark is just too low and it causes the engine to "bog down" when at high-speed, high-cylinder airmass, low RPM situations. I will definitely report my findings after I mess with the spark a little...

Thanks again.

[gmtech16450yz]

Someone can correct me if I'm wrong here, but it's always been my understanding that running low timing is worse than high timing on DI platforms? I also know that the knock parameters on these motors are overly sensitive and you could be experiencing a fuel knock instead of a spark knock - just some other things to think about and why lower timing might be worse than higher on these?

Nailed it! I used to drive people tuning LNF's bonkers when they'd be fighting KR and I'd tell them "Advance the ign timing and lean it out!"
I'm not saying that's exactly what's happening with your particular situation, but it is possible to retard the ign timing too far and get the mixture too rich on DI engines and actually create KR.

[jtrosky]

Very interesting! I would have never guessed that I should be advancing the spark instead of retarding it to avoid KR! :-)

Thanks again - this is great info. I really appreicate the assistance and I'll let you know how things go.

It was driving me crazy how I run 93 octane gas but was still getting considerable KR in certain places! This explains why...

I've been trying to attack the KR by both retarding the spark and/or adjusting the shift points and TCC lockup tables to try and avoid certain parts of the timing table - thinking that the KR might have been caused by engine "lugging". But obviously that was more of a workaround than a solution to the problem... It sounds like the real soluton here is to advance the spark instead of retarding it.

Go figure! :-)

Thanks again.

[gmtech16450yz]

DI has some very different aspects when it comes to tuning. I've been telling the Gen 5 guys that if they want to learn more about tuning the Direct Injected V/8's, read through some of the old threads in the 4cyl/ LNF sections. LNF's had DI, a turbo, factory wideband AND variable intake and exhaust cam timing. They used the Bosch E69 ECM that was pretty advanced in what it was capable of. There was A LOT of learning going on there, and amazingly enough, it looks like a few smart guys are continuing to pass along vital information to anyone on here that wants it. (Something that makes me HELLA PROUD to have been a part of BTW.) Discoveries made on the LNF years ago definitely carry over to the Gen 5 V/8's.

[jtrosky]

Well, time for me to fess up - I'm actually tuning a V6 DI engine (3.6L LFX). :-) I've just found that so many more knowledgeable people exist in the V8 forums so I put a lot of "general" type questions in the V8 section at times - questions that aren't really V6/V8 specific like this thread. It's really hard to get answers in the V6 forums...

[gmtech16450yz]

lol. Nothing wrong with that! I guess I should have included V/6's in the mix. And yeah, sometimes the good answers aren't in the places you would expect them to be in. Good luck!

[Redline MS]

This is all valid points as an overly rich chamber at low speed and under sparked is the recipe for "pre-ignition". I look at the biproduct of PI as the same as detonation ,which is induced by spark advance and improper firing relative to the crank cycle.

Since DI motors have high compression its not hard to "light off" the excess (or rich) mixture before the spark lights...this condition ,like detonation, can raise cylinder pressure to high levels and promote knock.

Many of the blow up engines I have seen discussed on line can be tied to this situation as well as incorrect lambda readings due to the misunderstanding of injection timing.

[jtrosky]

Well, so far, I'm not getting good results from increasing the timing (from stock values). I first increased the timing signifgantly (adding between 4 and 6 degress for the most part) and the KR got significantly worse. I've tried lowering these new timing values a little at a time and as of now, I'm down to stock+ .5 degrees and/or equal or lower than stock. Still need to test these latest values. But it doesn't appear that increasing the timing is the solution in my case.

The areas that I'm concerned about are very consistent - 1200rpm @ low-mid airmass values (where stock VCP timing is VERY high (11-13 degrees) and 1600-1800 @ high airmass areas (mainly when trying to increase speed slightly or maintain speed when in 5th or 6th gear with TCC locked). I'm not too concered with an occasional 4 or 5 degree KR, but in the areas that I mentioned above, it's constant KR until I move out of the RPM/airmass area. Very concerning...

Going to continue to reduce VCP spark values and/or adjust shift points/TCC lock/unlock speeds to see if I can get this corrected. I seem to be able to resolve the 1200rpm @ low airmass KR by significantly reducing the VCP timing (11-13 degrees down to 4-6 degrees) and adjusting the shift speeds and TCC lock/unlock speeds a little. Still need to figure out a solution for the 1600-1800 RPM/high airmass KR.

I'm using all stock values for fueling, so I woudn't expect the issue to be there, but who knows...

Will report my findings as I test more.

Thanks for the input! I'm all ears if anyone has any more suggestions! :-)

[jtrosky]

Well, my latest tune revisions seemed to do really well on my first drive with it. I think the "solution" is a combination of manually "smoothing" the VCP Spark table, adjusting the shift points and adjusting the TCC lock/unlock parameters. Basically, I think it boils down to the engine "lugging" in the trouble area. I think that the combination of my Driver Demand, shift point and TCC lockup modifications were causing the engine to "lug" in certain scenarios.

So, it's still a work-in-progress, but I'm definitely starting to see some positive results. The 1200rpm KR always existed even with a stock tune, but I think my modifications caused the 1600-1800rpm KR issues.

Thanks again for everyones input!

By the way, here is my current and stock tune if you guys want to have some fun laughing at my tuning capabilities (I'm learning, so be nice!). Also up for some recommendations as well! Just keep in mind that I'm going for a daily-driver, comfort-based tune (car is 100% stock mechanically) - not an all-out performance tune!

20160302_CustomTune-VCPSpark_Decreases-v1.92.hpt
JTsImpala-Stock.hpt

[jtrosky]

Well, I may have spoken too fast. While reducing the timing in some cells defintiely helped reduce KR, I'm finding that increasing the timing *slightly* in other cells may be the anwer for other areas (raising 1 degree instead of 4 or 5 resolves the issue). So I guess that you just have to find that "sweet spot" - it seems that just removing a bunch of timing isn't necessairly the best way to see if knock is false knock or not - or to try and stop real KR with DI engines (like it seems to have worked for non-DI engines)...

I have a question for you guys... I still get KR "spikes" of 5 degrees here and threre that seems kinds of "random" - it will give me 5 degress of KR and then the KR just goes back down to 0 naturally without any more "increases" in the KR. I may get it on one cell once out of 500 hits for example. I'm assuming that these "spikes" should be ignored if they are not repeated and frequent in one particular cell? It just seems like I don't see these strange "random" spikes when reviewing other non-DI logs and wanted to see if they were considered "normal" on DI engines...

[Higgs Boson]

Maybe it's not even coming from your main spark tables....there are a lot of modifier tables.

[jtrosky]

Actually, I'mm not even modifying my main spark tables at all. I'm adjusting the amount of timing added/removed in the VCP Spark modifier table. That is the main source of timing changes when above say 1000 RPM (table is active at almost all cam positions via the cam position multiple tables) - it's only inactive when the cam position is less than 2 degrees (I think - I'd have to confirm that). I may also be using the incorrect terminology... But basically, the VCP spark modifier table is almost always active....

I'll post a short log shortly... Would love for someone to take a look at it to see if they think any of the KR is very troubling...

Thanks.

[GHuggins]

You have to keep in mind that these are torque biased ecm's........ In other words you might not have any knock at all and with the torque model setup like it is, it will cause "false" KR to be seen... Not to mention these things are extremely delicate with the knock parameters... I know it's heavily frowned upon and I'm trying to figure out the absolute "most" correct way to go about this, but try increasing either your airmass tables a very minor 3 to 5% or your eq ratio table a very "small" amount and see if anything at all changes... Do not do both at the same time...

If it's "heard" knock, then back off timing and/or fueling in the given "trouble" areas... ALSO since the air models are directly related to the torque model, make sure there are NO humps or dips in either the MAF or VE tables in the "trouble" areas... 3 or 4 degrees of KR randomly in these, "I" consider a little normal - anything over that, try to see what you need to fix

[jtrosky]

First off - thank you guys very much for taking the time to help this novice! :-) I truly am a novice and am just "learning as I go". I'm obviously going very cautiously because I am a novice.

The car that we are discussing is a 2012 Impala (3.6L LFX direct-injected engine - same engine as the V6 Camaros with a 6T70 trans) - just waned to mention that as it may change the thinking a little since I'm posting in a V8 forum!

I know that my MAF curve is nice and smooth (actually using the stock MAF curve currently). I'm sure it could be refined, but it should be OK. I have absolutely no experience with VE tuning and I'm pretty sure all of my VE tables are zero'd out from the factory.

When we start talking about modifying airmass and EQ ratio tables is where we start getting beyond my experience level! :-)

Let me go ahead and post the current tune along with a short log showing some of the KR that I'm talking about and I would love to get your input as to whether or not I should even be worried about or not.

Again, thank you both very much - I will post the tune and a short log very shortly.

[GHuggins]

Guess we jumped the gun. What all has actually been done to the car. Stock and just making up a tune?

[jtrosky]

Car is 100% stock mechanically. I started with a stock tune and just started modifiying things for "comfort" (not performance"). I then started monitoring more and more and saw a lot of KR. I was able to eliminate a substaial amount of KR in circumstances where the engine would "lug" with the stock tune (by modifying the shift points and TCC lock/unlock tables), but I still get a lot of somewhat-random KR. Again, my apoligies for not posting the tune and/or log yet - I will do that very shortly (I promise) - involved with some work issues right now.

Thanks again!

[jtrosky]

So finally, here are some files to review...

I've included two tune files, version 1.95 and 1.96, along with two relatively short log files, one with 1.95 tune and one with 1.96 tune. The only differences between the two tunes are small VCP Spark changes to try and fix the KR I saw in 1.95. I also included my stock tune and my scanner config file (all 2.24 stuff).

Now these are short drives, but should give some idea of the type of KR I experience. All non-PE stuff, so mostly closed-loop (does go into open loop at times while coasting though).

Very interested to hear if I should just ignore this KR or if I should continue to try to "battle" it. Like I said, I really don't mind the occasional spike, but I really hate it when the KR bounced up and down for a few seconds. Not worried about performance - just don't want to cause any un-needed damage to engine longterm if I can avoid it. I never actually hear knock...

Thank you!!

[jtrosky]

Could only attach 5 files. So here is my Scanner config file if it helps... Thanks again!

Remember - go easy on me and my tune - I'm a novice!!! :-)