Timing and Knock. Ugly stuff

[kwhiteside]

So I'm doing some AutoMAF runs and notice in my logs that I consistently start getting knock with the same symptoms. I'm getting in it, and then the spark timing starts to drop while I'm still in it, the know always coincides with the spark drop.

See two images of examples and my tune and log.

Thanks for any help you can give. Pointing me the right direction or making a recommendation would be great.

Perhaps an explanation of why spark drops as you are getting into it. I'm guessing there is some rpm based table that tells it to drop the faster you go. My engine doesn't seem to like that drop.

[dfe1]

Base spark timing is referenced to engine load (airflow-grams/cyl). If you're going to chase timing issues, it would be helpful to log grams/cyl so you can compare commanded to actual timing. Then you can determine whether the drop in timing is a result of what's being commanded or if one of the correction tables is coming into play.

[joecar]

The PCM sees knock, determines the amount of retard required (KR), and then subtracts this from the current timing which is why SPARKADV drops.

(SPARKADV drops by KR amount).

[kwhiteside]

Base spark timing is referenced to engine load (airflow-grams/cyl). If you're going to chase timing issues, it would be helpful to log grams/cyl so you can compare commanded to actual timing. Then you can determine whether the drop in timing is a result of what's being commanded or if one of the correction tables is coming into play.

I logged DYNCYLAIR, just not on the dash. New learning for me. Is that what you are looking for, and what do I do with it?

[kwhiteside]

The PCM sees knock, determines the amount of retard required (KR), and then subtracts this from the current timing which is why SPARKADV drops.

(SPARKADV drops by KR amount).

So you are saying the knock wasn't because of the less spark, but rather the engine was protecting itself and dropping the spark?

[Highlander]

Engine is too lean and its knocking.

[GAMEOVER]

I think your engine is running lean too, your spark advance isn't really aggressive...

[kwhiteside]

I did another log run tonight. Still knock. I'm getting pretty confused and scared about this. I highlighted four instances in my log where knock happens.

My wideband is getting pretty close to commanded which should be a good thing.

Sometimes my wideband reports me running richer than commanded as in the drag gears screen shot where I launced getting onto the highway thru the gears. Should look familiar to you drag strip guys (rolling start). I know you all agree I'm running lean and that makes sense, but since wideband and commanded are getting so close, don't know what to do.

Keep in mind I'm running purely off MAF, in AutoMAF tuning mode.

My MAF bens still recommend more tweaks, but I don't see how that will affect my knock. Eventually I'll have AFR and commanded right on, and still be knocking the way things are going.

[dfe1]

The knock you're getting isn't all that severe, and it isn't staying very long, so I wouldn't worry too much about engine damage. What the knock readings indicate is the amount of retard the PCM is commanding to eliminate knock. So in essence, the only time true knock is present is the short time interval between when the sensor picks up "noise" and the PCM pulls spark. However, it's obviously prudent to eliminate as much knock as possible.

Spark is only one component contributing to the occurrence of knock-- air/fuel ratio is another. As Highlander has pointed out, your mixture is a bit lean, which could be the major cause. Shoot for an AFR of 12.5 to 12.8:1 at wide open throttle.

Of course, the question that hasn't been addressed yet is fuel. Low fuel octane is one of the most common causes of knock. Everyone has a different opinion about which type of pump gas is best, but I've found that in the Southeast, Chevron is the best choice. I've seen any number of cars that had knock issues with other brands, and those issues disappeared after swithing to Chevron premuim.

Also, it doesn't really matter if wideband and commanded are identical, if commanded is too lean. What that means is that you've tuned correctly to the wrong value.

[Highlander]

On a stock 2001 Z06 @ 4000 rpm you will NOT be able to command 25º total advance.. Sorry.. Drop your timing and richen up the mixture.

[joecar]

Summary from what was said so far:
- richen AFR,
- reduce timing,
- change gasoline brand,

Also check:
- oil ingestion,
- check spark plug gap (make it a bit smaller).

[Highlander]

How is spark plug gap going to help with detonation?

[kwhiteside]

On a stock 2001 Z06 @ 4000 rpm you will NOT be able to command 25º total advance.. Sorry.. Drop your timing and richen up the mixture.

Thanks for your advice Highlander.

I'm new to timing so please bare with me if I'm slow.

I grabbed another tun for a 02Z06 from the holdensite (whatever it is) and found the timing in the B5913 HO table does drop down in my areas of detonation. I have no idea why mine is as high as it is, came that way. So you are suggesting I tweak B5913 lower in the knock ranges?

Also, from the tutorials, my LO table is a mirror of my HO table. How do you know weather the pcm thinks you have high octane or low ( what do you monitor for that) ? Is it possible my car is detecting LO or somewhere in between and should be getting values from the LO table or an avg of the two, but mine are identical???

Thanks in advance, Ken . . .

[Highlander]

You have to watch out because if you lower your HO table and your LO table is higher than your HO timing will get a bit crazy...

Copy high to low and drop 5º to low. that should help tremendously.

On a intake/headers z06 2002 I gained 20rwhp with my tune.