How does burst knock work?

 

Basically, how it was explained to me is "anticipated knock "

 

When it sees a large step in cylinder air mass (which
follows MAP pretty much) it pulls back timing right
away rather than waiting to receive knock sensor
complaints.

The threshold for triggering is delta CylAir and if you
want to see this quantity, try using Excel (I don't
know if the custom PIDs will let you compute based
on previous frame values) as =(CylAir2-CylAir1)/8
for 10 frame/sec rate, /16 for 5/sec and /4 for 20/sec
(over 24 PIDs falls to 5/sec and under 12 will give you
20/sec frame rate). You can plot this in time and see
what the normal delta on throttle-mash is, and more
to the point you can look for opening-throttle events
that produce KR blips and figure out where to put a
BK threshold (if you prefer this to a fatter speed density
mixture than might be "proper" to cover the lean hole,
which is usually the real cause of tip-in knock).

 

ahh so this is probably why i get like 5-8* of knock in my truck if i hammer on it while moving, especially at highway speeds? the surge of air from the s/c (sorry to hi-jack)

 

Jimmy,
Why is it that burst knock will will show , but their is no retard recorded?

 

It should show both in a less-than-HO-table advance value
and in the burst knock retard PID. If it's active. I discovered
it by the former, working on a truck before the burst knock
retard PID was a scanner option (couple of years ago, now).
It does not show in the knock retard PID, it has its own
(and there are other retard PIDs too as I recall). If you have
a mysterious timing shortfall you should log all of the retard
and advance PIDs you can get ahold of and then discard the
ones that are always 0.

 

I did Jimmy,
The only one showing any retard is the burst knock.
Correct me if I am wrong, but busrt knoc is a retarding device correct? If so why dosnt the retard pid show the degrees of burst knock present?

 

Because they are two seperate systems. The KR .pid is timing pulled based on what the knock sensors report and the knock sensor settings in the PCM. BK is timing pulled based on changes in airflow and settings in the PCM. As long as certain conditions are met, timing will be pulled - with or without the presence of detonation, ping, etc.

 

so the retard pid isnt too the knock retard pid, like base advaced is too advance sae