Surging with high overlap cams any solution?
Surging is coming from something being too slow. A poor
mixture/spark position, a punked-out low-RPM charge
with a lot of overlap-reversion "EGR" and stuff like that
make the motor slow to move. It drives the control loops
nuts.
Surging likes to have some mistune to pluck its string. Like
if you have a timing table with large swings in the MAP
dimension, then MAP pulsation (from big cam and stumbling)
jitters timing around. If tune is in a place where output is
timing-sensitive (either short or long, improve or degrade with
more spark) then change in burn character, speed, evacuation
before the fill and so on drive back to the MAP and around
you go.
There are all these PID variables that are supposed to be for
filtering against all this jigginess but I don't understand it any
more than superficially.
Fueling swing with MAP via some low-end VE table error is
another reach-around. If your 400Hz VE value leads you to
an increasing misfueling as you approach it from idle and
cruise position, low sinks you lower and it's a yo-yo. This
is something you may not tune and you may see very little
data for in scans. But it can destabilize things, I've seen it.
https://ls1tech.com/forums/showthrea...&highlight=map
If you spent the time to "Cadillac it down" like with the scan
tool bidirectional controls, hold the IAC air and the spark and
the EQ and tweak these to where you need the least air to
run (min MAP) and keep lowering the RPM, see what VE
value makes it all right there, it might be able to gain some
manners.
Something to do in the garage when it's too rainy to drive.
mixture/spark position, a punked-out low-RPM charge
with a lot of overlap-reversion "EGR" and stuff like that
make the motor slow to move. It drives the control loops
nuts.
Surging likes to have some mistune to pluck its string. Like
if you have a timing table with large swings in the MAP
dimension, then MAP pulsation (from big cam and stumbling)
jitters timing around. If tune is in a place where output is
timing-sensitive (either short or long, improve or degrade with
more spark) then change in burn character, speed, evacuation
before the fill and so on drive back to the MAP and around
you go.
There are all these PID variables that are supposed to be for
filtering against all this jigginess but I don't understand it any
more than superficially.
Fueling swing with MAP via some low-end VE table error is
another reach-around. If your 400Hz VE value leads you to
an increasing misfueling as you approach it from idle and
cruise position, low sinks you lower and it's a yo-yo. This
is something you may not tune and you may see very little
data for in scans. But it can destabilize things, I've seen it.
https://ls1tech.com/forums/showthrea...&highlight=map
If you spent the time to "Cadillac it down" like with the scan
tool bidirectional controls, hold the IAC air and the spark and
the EQ and tweak these to where you need the least air to
run (min MAP) and keep lowering the RPM, see what VE
value makes it all right there, it might be able to gain some
manners.
Something to do in the garage when it's too rainy to drive.
Try alot less timing (14-20* where the stock table shows in the 43-45* range) in the problem area and fatten up the AFR to about 13.0-13.5:1. Worked on my car after many many hours of tuning and banging my head against the wall..
Originally Posted by 98Z28CobraKiller
Try alot less timing (14-20* where the stock table shows in the 43-45* range) in the problem area and fatten up the AFR to about 13.0-13.5:1. Worked on my car after many many hours of tuning and banging my head against the wall..
This is what my spark table looks like.
Nope nothing noticable. What is funny is that my stock tune had a similar dip. In an earlier tune I got rid of it but when I put it back and adjusted it to my cam's sweet spot, my drivability went from good to great. Here is my stock table.
Originally Posted by SSpdDmon
What about the transition between 2000 and 2400 rpms? You don't feel any jerking jumping from 21 to 42 degrees in a 400 rpm span?
I would smooth out this area just to make the 3d graph look pretty. Realistically though, you probably never hit those low cyl air mass cells during normal driving at rpms over 2400 except maybe on decel with the car in gear.
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