How to eliminate the detonation at tip-in/half throttle? LS1 Edit
09-08-2004, 04:18 PM
#1
How to eliminate the detonation at tip-in/half throttle? LS1 Edit I just bought a 1998 z28 with 120,000 miles and it has all the bolt ons, head/cam, stall, and was tuned by 2 good tuners with LS1 Edit. I thought it was just running really lean but I just talked to the previous owner and he said
what happens is when driving the car around town I speed up and push the gas at half throttle it sould like pinging but louder so it must be detonation. Also what could cause this and maybe need to be replaced?
Between the two of them they were able to get more
horsepower out of the head/cam job, but neither of them could
completely
eliminate the detonation at tip-in.
horsepower out of the head/cam job, but neither of them could
completely
eliminate the detonation at tip-in.
09-08-2004, 05:52 PM
#2
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You can up the VE values at midband where you find
tip-in; fake things a bit rich on transitions. You can
also apply "just enough" burst knock so suppress
ping / KR (it will pull timing but then go away). Also
want to check for any signs of lean midband running
(which you don't get to see on the dyno unless it
is a load type, not an inertial) - positive trims on any
of the middle to upper cells indicates that any time
the loop is opened (as on throttle transients) there's
a lean hole underneath. Last, you can log the RPM
and the dynamic cylinder air that is seen right before
ping/KR pops up, and shave back a degree or two of
timing specifically in those main timing table cells that
look to be responsible. Though this may result in a
less aggressive timing map than you could get away
with, if you fattened the VE and maybe covered up
with a little (1-2 degrees?) of burst knock pull.
tip-in; fake things a bit rich on transitions. You can
also apply "just enough" burst knock so suppress
ping / KR (it will pull timing but then go away). Also
want to check for any signs of lean midband running
(which you don't get to see on the dyno unless it
is a load type, not an inertial) - positive trims on any
of the middle to upper cells indicates that any time
the loop is opened (as on throttle transients) there's
a lean hole underneath. Last, you can log the RPM
and the dynamic cylinder air that is seen right before
ping/KR pops up, and shave back a degree or two of
timing specifically in those main timing table cells that
look to be responsible. Though this may result in a
less aggressive timing map than you could get away
with, if you fattened the VE and maybe covered up
with a little (1-2 degrees?) of burst knock pull.
09-08-2004, 09:24 PM
#4
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Yeah, the one prior I figure (and maybe its neighbors too)
because the frame where you see KR, it's already been
computed up and applied - based on detecting ping at
some point before that "report".
because the frame where you see KR, it's already been
computed up and applied - based on detecting ping at
some point before that "report".
09-09-2004, 05:25 PM
#6
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Originally Posted by jimmyblue
Yeah, the one prior I figure (and maybe its neighbors too)
because the frame where you see KR, it's already been
computed up and applied - based on detecting ping at
some point before that "report".
because the frame where you see KR, it's already been
computed up and applied - based on detecting ping at
some point before that "report".
Dave
09-09-2004, 07:28 PM
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High rate of change on MAP puts the MAF offline
and you use the SD tune. Which on a mechanically
modified, software unmodified car is likely to be on
the lean side, when you're in the powerband.
If you see KR on throttle transients in a particular
RPMxCylAir cell, but that same cell is a happy camper
when you're pulling in 3rd/4th, I would suspect that
there is not a timing problem in that cell, but one
that it left from or traveled through. Like, you start
at 3000RPM and a CylAir of say 0.5, and when you
open the throttle all you do is slide the CylAir up
(RPM does not move instantly). You have to drag
that spark advance down from 35 to 25 as fast or
faster than the CylAir climbs. On a really sharp
throttle whack, maybe this doesn't happen quick
enough. A bit of burst knock applied right away
might get you safe, sooner. Though it might hang
around a bit longer than you'd like.
But anyway, I do think that when you're talking
about transient effects, a lot of the clues lie in
the recent past. Like on peoples' logs I see the
TPS transition, then O2s dip from 850 to 650 for
just one tick, and on the next tick a KR jump-up.
Thing is the OBD-II data stream is a real sparse
sample of all the stuff that goes on; I figure there
are probably ten or a hundred recalculations for
every one that gets reported out. I guess we have
to fill in the blanks by interpolation, trace a finger
from Cell N to Cell N+1 and see if maybe we ran
over a sharp transition that needs smoothed or
a late change that should happen early, etc.
I think another diagnostic thing to try is this -
try a sharp vs slow throttle apply, and see if the
slow roll-on eliminates the KR. If so then it's got
to be a transient fuel shortfall (likely VE) or
spark excess. And if you can further "subdivide"
the TPS-rate space with your foot and catch
logs of each, you might be able to slow down the
traversal of the "problem spot"(s) enough to really
pin down the cause/location.
and you use the SD tune. Which on a mechanically
modified, software unmodified car is likely to be on
the lean side, when you're in the powerband.
If you see KR on throttle transients in a particular
RPMxCylAir cell, but that same cell is a happy camper
when you're pulling in 3rd/4th, I would suspect that
there is not a timing problem in that cell, but one
that it left from or traveled through. Like, you start
at 3000RPM and a CylAir of say 0.5, and when you
open the throttle all you do is slide the CylAir up
(RPM does not move instantly). You have to drag
that spark advance down from 35 to 25 as fast or
faster than the CylAir climbs. On a really sharp
throttle whack, maybe this doesn't happen quick
enough. A bit of burst knock applied right away
might get you safe, sooner. Though it might hang
around a bit longer than you'd like.
But anyway, I do think that when you're talking
about transient effects, a lot of the clues lie in
the recent past. Like on peoples' logs I see the
TPS transition, then O2s dip from 850 to 650 for
just one tick, and on the next tick a KR jump-up.
Thing is the OBD-II data stream is a real sparse
sample of all the stuff that goes on; I figure there
are probably ten or a hundred recalculations for
every one that gets reported out. I guess we have
to fill in the blanks by interpolation, trace a finger
from Cell N to Cell N+1 and see if maybe we ran
over a sharp transition that needs smoothed or
a late change that should happen early, etc.
I think another diagnostic thing to try is this -
try a sharp vs slow throttle apply, and see if the
slow roll-on eliminates the KR. If so then it's got
to be a transient fuel shortfall (likely VE) or
spark excess. And if you can further "subdivide"
the TPS-rate space with your foot and catch
logs of each, you might be able to slow down the
traversal of the "problem spot"(s) enough to really
pin down the cause/location.
