Idle surging problems, RAF/VE/Spark dialed in
Idle surging problems, RAF/VE/Spark dialed in On start up the AFR starts out in the mid 12's and idle's stable, after about 4 seconds it decays to the 14's where it starts surging and rolling around. Once the surging starts the afr typically goes from the 12's to the 17's, I can't even run Russ K's idle config without the thing stalling. The RAF and VE were both tuned prior so they should be close, I've played with timing and other variables I just cannot seem to get this thing under control. Until recently it was idling good, just having follower/cracker tuning issues that were causing very similiar symptoms, now no matter what I do I can't even get it to idle steady in the driveway. Put new plug's in it yesterday, resealed the intake(was thinking I had a leak), all out of idea's. trying to tune in OLSD.
This sort of "fuel surge" I think relates to a poor VE fit
along the MAP axis. Presuming you don't have PE set
up such that it could kick in at idle, which would be bad.
VE should increase with MAP, but if it has too high a
slope then more MAP adds fuel, which makes idle less
efficient, which raises MAP...
You might check this by experimenting, take the idle-
range columns and use the "normal" idle MAP as the
pivot, and build new MAP columns in Excel that have
varying slopes (less, and more, rise w/ MAP). See if
that gets you a lesser AFR oscillation (or ideally none).
Idle-range AFR on a cammed car is likely somewhat
spoofed by the overlap. It is not to be assumed, that
indicated-14.7 is actually 14.7, or that either one is
best-idle (other than according to the EPA). Leaner
usually idles tighter / cleaner.
Also be sure you are tuning idle with the adaptive
spark disabled. You could have garbage there, and at
best it it always trying to hide how bad things really
are. If you can idle OK without it, then you can use
it to clean up the last bit of instability. But if it's adding
spark to an already-maxed timing, it could hurt more
than help; ditto some lame factory profiles that quit
trying at high underspeed and lead to instability about
that point.
along the MAP axis. Presuming you don't have PE set
up such that it could kick in at idle, which would be bad.
VE should increase with MAP, but if it has too high a
slope then more MAP adds fuel, which makes idle less
efficient, which raises MAP...
You might check this by experimenting, take the idle-
range columns and use the "normal" idle MAP as the
pivot, and build new MAP columns in Excel that have
varying slopes (less, and more, rise w/ MAP). See if
that gets you a lesser AFR oscillation (or ideally none).
Idle-range AFR on a cammed car is likely somewhat
spoofed by the overlap. It is not to be assumed, that
indicated-14.7 is actually 14.7, or that either one is
best-idle (other than according to the EPA). Leaner
usually idles tighter / cleaner.
Also be sure you are tuning idle with the adaptive
spark disabled. You could have garbage there, and at
best it it always trying to hide how bad things really
are. If you can idle OK without it, then you can use
it to clean up the last bit of instability. But if it's adding
spark to an already-maxed timing, it could hurt more
than help; ditto some lame factory profiles that quit
trying at high underspeed and lead to instability about
that point.
At a glance at the file, I'd guess that base timing is too high there at 29deg.
Try setting your base timing and the low area of your main spark tables to something like 22-24deg and see what you get. You over-under speed spark tables may be a bit aggressive and feeding into this as well.
Try setting your base timing and the low area of your main spark tables to something like 22-24deg and see what you get. You over-under speed spark tables may be a bit aggressive and feeding into this as well.
Thanks for the responses. I spent some time on the VE table and lowered idle spark to 24 degrees and it helped out a lot. I never really realized the map axis point made, and cleaned things up a lot along the axis. When I disable adaptive idle spark it starts surging pretty bad, so I imagine something's still off that the idle spark is covering up. Another thing, should the IAC counts be swinging around while the surging is going on? the IAC freezes everytime this problem occurs and I'm not sure if that's normal procedure or not.
