Sudden burst knock? Why..?

[Chris81]

What would cause sudden burst knock?

Here is the deal.. the car i'm tuning right now was tuned before.. so I threw the WB on it and logged.. the timing stayed steady at WOT, but the AFR was off from commanded (sometimes a full point richer)

So, I started autotuning it in SD and OL.. i've dailed in the VE pretty close and the commanded/actual AFR at WOT throttle is almost dead on.. great right?

But, with the old tune the timing stayed fine (with the MAF/o2's) but it drove like crap.. now the fueling is better and there is alot of burst knock at WOT..

What would cause this? The only thing I see that looks like it goes in line with the burst knock while logging is the MAF airflow (but its mafless) and the cylair..

Why would going into SD and OL cause this?

[Blacky]

Can you attach a log file (*.efi) file, that shows the burst knock? That will give more info on why it might be happening.
Regards
Paul

[Chris81]

I can't get it to attach..

Would you like me to email it to you?

[Delco]

What would cause sudden burst knock?

Here is the deal.. the car i'm tuning right now was tuned before.. so I threw the WB on it and logged.. the timing stayed steady at WOT, but the AFR was off from commanded (sometimes a full point richer)

So, I started autotuning it in SD and OL.. i've dailed in the VE pretty close and the commanded/actual AFR at WOT throttle is almost dead on.. great right?

But, with the old tune the timing stayed fine (with the MAF/o2's) but it drove like crap.. now the fueling is better and there is alot of burst knock at WOT..

What would cause this? The only thing I see that looks like it goes in line with the burst knock while logging is the MAF airflow (but its mafless) and the cylair..

Why would going into SD and OL cause this?

I assume you are logging all the spark pids to ensure it is actually burst knock and not knock , burst knock will only normally happen when it sees a rate of change of airflow

[Chris81]

Yes, I was logging the EST spark pids.

[Delco]

Yes, I was logging the EST spark pids.

Cool the look for a change in airflow greater than the amount programmed into the table B6210 at the relevant revs , if the airflow is changing that much due to pulsations or a bumpy VE table ( the VE table is relevant in the speed density airflow calculations) then you need to lift the burst knock limits up a little.

[Chris81]

Cool the look for a change in airflow greater than the amount programmed into the table B6210 at the relevant revs , if the airflow is changing that much due to pulsations or a bumpy VE table ( the VE table is relevant in the speed density airflow calculations) then you need to lift the burst knock limits up a little.

Delco, would the MAF airflow have anything to do with it even though the MAF isn't enabled? The MAF airflow looks similar to the burst knock.. as does the cylair used for timing..

[Chris81]

Update..

I did some more tuning on the car today.. I pulled some timing while doing the autotuning so at WOT the AFR was plenty rich and the timing was commanding 24 degrees. I didn't log the burst knock this time but it was definately there.

Also, there are zero's as values in my B6210.. and 6212 is commanding to pull 6 degrees (these are stock values, unchanged)

So, does the use of a MAF mask this? The car never did this with the MAF enabled.. can it be because of the wide throttle opening of the TPIS 90 mm TB?

How do I adjust B6210?

[joecar]

Delco, would the MAF airflow have anything to do with it even though the MAF isn't enabled? The MAF airflow looks similar to the burst knock.. as does the cylair used for timing..
The MAF would be just following the airflow.

[joecar]

So, does the use of a MAF mask this? The car never did this with the MAF enabled.. can it be because of the wide throttle opening of the TPIS 90 mm TB?
With the old tune and MAF (see post #1), the VE table derived air never delta'd that steeply, so you never saw it.

With your new tune, VE table derived airflow is now more responsive so it will delta sharply enough.

The MAF may have had nothing to do with it.

[Chris81]

With the old tune and MAF (see post #1), the VE table derived air never delta'd that steeply, so you never saw it.

With your new tune, VE table derived airflow is now more responsive so it will delta sharply enough.

The MAF may have had nothing to do with it.

ahhh ok I see..

So, what do I do to correct it? I see the units are in grams.. but not g/sec

[Doc]

Trying to stay on topic...Chris how are you attempting to "attach" the file? If you acuire the screen shot you want and hit printscreen and then use Paint, MS Publisher, whatever picture editor you have and right click paste-whamo you should have your screen shot in the editor. Then save it as a .jpeg file, then go to the file attachment here. You have a file size limit of 244kb so you will probably have to parce down the original size.
There I can't remember who told me how to do that but that made life easier for me. Please try to upload what you are seeing, I would love to see it.

[TAQuickness]

Compress the log file (winzip) and it should attach.

[Chris81]

Here is the attachment, i'm going to do some more tuning on it in a bit.. i'll get one with more helpful PIDS, not just the spark stuff.

[SSbaby]

Are you running a custom OS? If so, ... this might be from left field but how have you set the {A00x} PIDs?

I ask this because my tune was giving me grief (pinging badly) when I was only running very mild spark. When I calibrated the {A00x} PIDs, I ran quite aggressive timing without running into any KR.

[Chris81]

Nope, this is a friend's car.. its just setup for autotuning (OLSD)

Although, I might use OSV3 when I get everything sorted out.. not sure yet.

[SSbaby]

How much Burst Knock are you running?

I've got mine set to just 2* after a lot of experimenting (i.e. will pull 2* of timing if PCM detects a huge difference in incoming air). No KR either!

[Chris81]

The table is still set stock for now

[SSbaby]

If it's stock then you are perhaps running too much burst knock... what is it 6-8*? Anyhow, most people tend to run it down to a few degrees and increase the delta airflow to around 0.040-0.060 g/s... some choose to run zero burst knock but I'm not sure of the 'potential repercussions'.

If you intend to run your burst knock at a higher threshold, you need to be confident of your timing settings.

[Chris81]

If it's stock then you are perhaps running too much burst knock... what is it 6-8*? Anyhow, most people tend to run it down to a few degrees and increase the delta airflow to around 0.040-0.060 g/s... some choose to run zero burst knock but I'm not sure of the 'potential repercussions'.

If you intend to run your burst knock at a higher threshold, you need to be confident of your timing settings.

I was wondering on how to setup the delta airflow, currently the table is zeroed out.. should I run .040-.060 g/s all the way down the table.. or just maybe here the burst knock is occuring? I was wondering on the units of measure as well.. it states grams.. but not g/sec so I was unsure.

[SSbaby]

I was wondering on how to setup the delta airflow, currently the table is zeroed out.. should I run .040-.060 g/s all the way down the table.. or just maybe here the burst knock is occuring? I was wondering on the units of measure as well.. it states grams.. but not g/sec so I was unsure.


I don't know if your deltas should be zeroed out? If the deltas are very low, it will engage burst knock more frequently... which means timing is pulled at the lightest of throttle inputs.

My delta curve starts at around 0.040g and ramps up gently at 0.060g. Other deltas that I've seen start at 0.040, peak at at 0.060g at the 1600-2000rpm range then trailing off at a flat 0.050g.

Pick your poison. Btw, try a low BKR of around 3* for starters and see how you go.

[Chris81]

Yea, I wondered about the deltas but on my car and the car i'm doing now they are at zero.. i'll try adjusting the BKR and see what happens.

[joecar]

The units are in grams;

the delta is not the air flow delta, but the cylinder air mass delta,
same as the Spark table axis (GM.DYNCYLAIR_DMA).

[Chris81]

ahh, that makes perfect sense now...

good deal.