Burst knock Retard?
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From: Tennessee Tech
Burst knock Retard? This is what he's explained to me over the phone:
A buddy is experiencing knock after installing a cam. He's got a tune on the car but he doesn't think the tuner tuned out the burst knock so that it'll stop pulling timing when it senses false knock because of the cam. I've never really looked into this and he asked me if i could tune it out for him, but i don't really feel comfortable since I've never done it before. What exactly do i need to do to the Burst knock tables to get rid of this false knock? There's "Enable Delta Cyl Air" and "Vs RPM".... I'm guessing I'd need to datalog and see how much knock its getting at what RPM, and go from there?
A buddy is experiencing knock after installing a cam. He's got a tune on the car but he doesn't think the tuner tuned out the burst knock so that it'll stop pulling timing when it senses false knock because of the cam. I've never really looked into this and he asked me if i could tune it out for him, but i don't really feel comfortable since I've never done it before. What exactly do i need to do to the Burst knock tables to get rid of this false knock? There's "Enable Delta Cyl Air" and "Vs RPM".... I'm guessing I'd need to datalog and see how much knock its getting at what RPM, and go from there?
Burst knock is meant to prevent ping when you
roll on the throttle. It is predictive, while knock
retard is reactive. The given explanation seems
bent to me.
If you want to see the Delta Cyl Air on the same
basis the PCM uses, you have to go to Excel and
divide the frame-frame difference by 8 (at 10/sec
frame rate) to put it on the PCM's 12.5mS "tick"
basis. Compare the numbers you see to the burst
knock thresholds. You will be well under it except
at tip-in and possibly during 1st gear WOT run-up.
I worked on a '99 GMC pickup that was cammed
and the burst knock was pulling out a lot of timing,
really dogged out the acceleration until I zeroed it.
Cams should not cause false or real knock. If he
has false knock he ought to be sure the valvetrain
is all properly adjusted. If he has knock retard the
mixture and spark ought to be checked before
calling it false. Take out 5 degrees advance and
see if it's still there, like.
There is a whole raft of loggable Spark Retard PIDs
and you can see which ones are bugging.
The thing I mention about the 1st gear run-up,
can be an artifact of the front slope of the VE table
(cylinder air ideally would be constant w/ RPM at
WOT, cam overlap makes this not-true at lower
RPM and the VE change accounts for most of the
delta when MAP is constant (WOT). Whether the
table is realistic or not, may play into BK triggering
somewhat.
I recall 0.02 being safely out of the way on a 5.3
motor and 0.01 being too busy, for thresholds.
roll on the throttle. It is predictive, while knock
retard is reactive. The given explanation seems
bent to me.
If you want to see the Delta Cyl Air on the same
basis the PCM uses, you have to go to Excel and
divide the frame-frame difference by 8 (at 10/sec
frame rate) to put it on the PCM's 12.5mS "tick"
basis. Compare the numbers you see to the burst
knock thresholds. You will be well under it except
at tip-in and possibly during 1st gear WOT run-up.
I worked on a '99 GMC pickup that was cammed
and the burst knock was pulling out a lot of timing,
really dogged out the acceleration until I zeroed it.
Cams should not cause false or real knock. If he
has false knock he ought to be sure the valvetrain
is all properly adjusted. If he has knock retard the
mixture and spark ought to be checked before
calling it false. Take out 5 degrees advance and
see if it's still there, like.
There is a whole raft of loggable Spark Retard PIDs
and you can see which ones are bugging.
The thing I mention about the 1st gear run-up,
can be an artifact of the front slope of the VE table
(cylinder air ideally would be constant w/ RPM at
WOT, cam overlap makes this not-true at lower
RPM and the VE change accounts for most of the
delta when MAP is constant (WOT). Whether the
table is realistic or not, may play into BK triggering
somewhat.
I recall 0.02 being safely out of the way on a 5.3
motor and 0.01 being too busy, for thresholds.
wow, i'm glad i read this post. my downpipe runs right under my k member and i sometimes get knock and have been trying to figure it out for awhile!!!
