Question on what tables control getting the best idle.
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From: Lake Tapps, WA
Question on what tables control getting the best idle. My sharp as a bowling ball brain is having trouble understanding what controls smooth stable idle. Let's take a 390 with a 236/236 .587/.587 cam as a example.
Let's say your IAC count is in the envelope ( I think it's 60)
Your fuel trims are almost 0, closed loop
Besides timing what tables would you tweek to get the best idle? I'm just asking from experience what do you tweek?
Let's say your IAC count is in the envelope ( I think it's 60)
Your fuel trims are almost 0, closed loop
Besides timing what tables would you tweek to get the best idle? I'm just asking from experience what do you tweek?
My sharp as a bowling ball brain is having trouble understanding what controls smooth stable idle. Let's take a 390 with a 236/236 .587/.587 cam as a example.
Let's say your IAC count is in the envelope ( I think it's 60)
Your fuel trims are almost 0, closed loop
Besides timing what tables would you tweek to get the best idle? I'm just asking from experience what do you tweek?
Let's say your IAC count is in the envelope ( I think it's 60)
Your fuel trims are almost 0, closed loop
Besides timing what tables would you tweek to get the best idle? I'm just asking from experience what do you tweek?
you can adjust the PID loop for the idle corrections........also direct idle and learned idle parameters......i usually reduce them with large cam cars and 0 out the 20rpm error area cause 20rpm jump is normal for a cam car......also the learning delay i move form 1.3sec to 4sec for that same reason
Thread Starter
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From: Lake Tapps, WA
OK, what does perfect fueling mean? Does it mean your fuel trims are close to 0? Didn't know that excessive timing caused issues with a stable idle.
Number one in my experience is the primary VE table, the
400 and 800 RPM columns. With high overlap cams these
get real bent and the motor's blow-through and reversion
are higher, meaning the MAP-axis and RPM-axis fit are
not right. The MAP-axis fit gives fuel surging in itself. The
RPM slope is hard to fit because you can't idle at 400RPM,
you have to cut and try.
Do this with adaptive spark turned off, and you'll see how
bad it really is.
Fuel trimming is also whacked because of shot-through
air, and you probably want to tamp down the O2 sensor
switchpoints at the very low airflows. Try 300mV or so
as a start. Wideband indicated AFR is also bent by the
excess exhaust air, so you want to go by what makes
MAP minimum (max vacuum) just like old school, see
what that average NB O2 voltage is, and use that voltage
as the closed loop target.
When you've got the idle as clean as you can without
the adaptive spark, then turn it on and straighten it
out - pay attention to the profile, some OSes have it
climb in the undeerspeed table up to a point, and then
drop back to zero; if you ever get above that error RPM
you'll go unstable just from that (leaving aside that net
timing > MBT is also destabilizing).
400 and 800 RPM columns. With high overlap cams these
get real bent and the motor's blow-through and reversion
are higher, meaning the MAP-axis and RPM-axis fit are
not right. The MAP-axis fit gives fuel surging in itself. The
RPM slope is hard to fit because you can't idle at 400RPM,
you have to cut and try.
Do this with adaptive spark turned off, and you'll see how
bad it really is.
Fuel trimming is also whacked because of shot-through
air, and you probably want to tamp down the O2 sensor
switchpoints at the very low airflows. Try 300mV or so
as a start. Wideband indicated AFR is also bent by the
excess exhaust air, so you want to go by what makes
MAP minimum (max vacuum) just like old school, see
what that average NB O2 voltage is, and use that voltage
as the closed loop target.
When you've got the idle as clean as you can without
the adaptive spark, then turn it on and straighten it
out - pay attention to the profile, some OSes have it
climb in the undeerspeed table up to a point, and then
drop back to zero; if you ever get above that error RPM
you'll go unstable just from that (leaving aside that net
timing > MBT is also destabilizing).
yes in open loop you should be right at your target afr......very high idle timing 25ish and up can cause unstable idle because usually the air requirement drops alot and its more difficult to meter
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Thread Starter
10 Second Club
iTrader: (27)
Joined: Sep 2008
Posts: 2,229
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From: Lake Tapps, WA
Number one in my experience is the primary VE table, the
400 and 800 RPM columns. With high overlap cams these
get real bent and the motor's blow-through and reversion
are higher, meaning the MAP-axis and RPM-axis fit are
not right. The MAP-axis fit gives fuel surging in itself. The
RPM slope is hard to fit because you can't idle at 400RPM,
you have to cut and try.
Do this with adaptive spark turned off, and you'll see how
bad it really is.
Fuel trimming is also whacked because of shot-through
air, and you probably want to tamp down the O2 sensor
switchpoints at the very low airflows. Try 300mV or so
as a start. Wideband indicated AFR is also bent by the
excess exhaust air, so you want to go by what makes
MAP minimum (max vacuum) just like old school, see
what that average NB O2 voltage is, and use that voltage
as the closed loop target.
When you've got the idle as clean as you can without
the adaptive spark, then turn it on and straighten it
out - pay attention to the profile, some OSes have it
climb in the undeerspeed table up to a point, and then
drop back to zero; if you ever get above that error RPM
you'll go unstable just from that (leaving aside th
at net
timing > MBT is also destabilizing).
400 and 800 RPM columns. With high overlap cams these
get real bent and the motor's blow-through and reversion
are higher, meaning the MAP-axis and RPM-axis fit are
not right. The MAP-axis fit gives fuel surging in itself. The
RPM slope is hard to fit because you can't idle at 400RPM,
you have to cut and try.
Do this with adaptive spark turned off, and you'll see how
bad it really is.
Fuel trimming is also whacked because of shot-through
air, and you probably want to tamp down the O2 sensor
switchpoints at the very low airflows. Try 300mV or so
as a start. Wideband indicated AFR is also bent by the
excess exhaust air, so you want to go by what makes
MAP minimum (max vacuum) just like old school, see
what that average NB O2 voltage is, and use that voltage
as the closed loop target.
When you've got the idle as clean as you can without
the adaptive spark, then turn it on and straighten it
out - pay attention to the profile, some OSes have it
climb in the undeerspeed table up to a point, and then
drop back to zero; if you ever get above that error RPM
you'll go unstable just from that (leaving aside th
at net
timing > MBT is also destabilizing).
Didn't know about lowering the O2 switching, your bringing up the exact points that make it such a mystery to me. Basically the pcm is getting bad data and that's what it's making it's corrections on.
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