Misfire and stumble on launch
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From: Michigan (Macomb or Lansing)
Misfire and stumble on launch My car seems to really fall on its face when I do a launch at like 2000 rpms give or take. I realize it should stumble the slightest bit because that isn't a ton of momentum, but it REALLY falls on its face and misfires about every time.
I gotta go through and check the fueling but it is a hard area to tune because it is only there for a split second.
I know I should probably post a tune and log of this but I haven't gotten around to it. Anything to look out for/change?
I gotta go through and check the fueling but it is a hard area to tune because it is only there for a split second.
I know I should probably post a tune and log of this but I haven't gotten around to it. Anything to look out for/change?
Have you tried launching at a higher rpm? Knowing what the fueling is doing here as well as spark would be key. Maybe just try logging a couple parameters like air fuel, spark and rpm that way you get max resolution.
There should be no stumble. Looking at the O2 sensors
at / after the stumble ought to yield some clues. Often
a "lean dip" can be seen at tip-in which then makes a
knock event and bog. You can fix the KR sensitivity and
decay, but you want to also prevent knock. On a MAF
type setup, tip-in drops you back to SD mode and any
lean discrepancy there may account for a lean dip; says
that the low RPM high MAP region wants help (a hard
place to get data, and bothered by everything else changing
meanwhile).
This may be cut-and-try territory, see where the MAP is
jumping to, whether increasing the VE in the cells you
are passing through helps any, if so the feather in the
neighbors and try to build a smooth clean table that is
better at the outlier positions.
The transient fueling might have something for you if
the manifold & heads are changed from stock, but I
don't know what specifically. I know I got to bog free
by just working the VE (and making the KR attack /
decay less twitchy).
Anyway, start with the scans and see what it's trying
to tell you.
at / after the stumble ought to yield some clues. Often
a "lean dip" can be seen at tip-in which then makes a
knock event and bog. You can fix the KR sensitivity and
decay, but you want to also prevent knock. On a MAF
type setup, tip-in drops you back to SD mode and any
lean discrepancy there may account for a lean dip; says
that the low RPM high MAP region wants help (a hard
place to get data, and bothered by everything else changing
meanwhile).
This may be cut-and-try territory, see where the MAP is
jumping to, whether increasing the VE in the cells you
are passing through helps any, if so the feather in the
neighbors and try to build a smooth clean table that is
better at the outlier positions.
The transient fueling might have something for you if
the manifold & heads are changed from stock, but I
don't know what specifically. I know I got to bog free
by just working the VE (and making the KR attack /
decay less twitchy).
Anyway, start with the scans and see what it's trying
to tell you.
