Car stumble from a dig
Teching In
Joined: Oct 2009
Posts: 9
Likes: 0
Look at what your timing is doing, I had an issue where if I jumped on it at low speeds my timing would fall to 8 or 9*, stumble, then jump back up and take off. I found that my high octane spark table fell off at low rpm and high air flow.
The dyno is a poor tool for chasing transient-throttle
/ drivability problemsm like what you describe.
Idle-range operation is often the first thing to suffer
from airflow mods, and secondary effects such as
O2 sensor false-trimming. If you're trimmed way
positive (like a sleepy O2 sensor will cause, or a
simple VE tune fidelity problem at the low end) the
WOT fueling when you leave from idle will lock in
that high fuel adder and everything is whacked in
a way that won't show up on the rollers with a
slow roll-on of throttle position (is the operator
really going to mat it and try to spin? Doubtful).
But then if you prop up the idle and are in a trim
cell where things are cleaner, you don't get the
same level of excess enrichment.
You want to see fuel trims at WOT with the two
"styles of WOT entry", and if you find high trimming
then you get to chase the cause.
/ drivability problemsm like what you describe.
Idle-range operation is often the first thing to suffer
from airflow mods, and secondary effects such as
O2 sensor false-trimming. If you're trimmed way
positive (like a sleepy O2 sensor will cause, or a
simple VE tune fidelity problem at the low end) the
WOT fueling when you leave from idle will lock in
that high fuel adder and everything is whacked in
a way that won't show up on the rollers with a
slow roll-on of throttle position (is the operator
really going to mat it and try to spin? Doubtful).
But then if you prop up the idle and are in a trim
cell where things are cleaner, you don't get the
same level of excess enrichment.
You want to see fuel trims at WOT with the two
"styles of WOT entry", and if you find high trimming
then you get to chase the cause.
