Throttle Cracker disabled due to hanging RPM, now RPM drops too fast!
04-19-2017, 01:55 PM
#1
Throttle Cracker disabled due to hanging RPM, now RPM drops too fast! 2000 Camaro with 6.0L and a small cam, 6 speed
Before when I would push the clutch in, while driving, the idle would hang at about 2k rpm
So I went in and disabled the throttle cracker, which fixed the issue - but now when I'm driving and push the clutch in, the rpm drops heavily and sometimes the engine dies completely
Do I need to add to base running airflow to correct this?
Before when I would push the clutch in, while driving, the idle would hang at about 2k rpm
So I went in and disabled the throttle cracker, which fixed the issue - but now when I'm driving and push the clutch in, the rpm drops heavily and sometimes the engine dies completely
Do I need to add to base running airflow to correct this?
04-21-2017, 03:29 PM
#3
I re enabled it BUT I noticed it still does it badly, but only when the ac is on. I can be rolling in neutral and it will be a 2k rpm hanging, once I turn the AC OFF the idle drops down to normal..
reduce ac air in the tune maybe?
Last edited by TXjeepTJ; 04-21-2017 at 03:48 PM.
04-21-2017, 09:51 PM
#4
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A/C imposes an airflow adder based on a guesstimate of
compressor drag torque (see IAT dependence and A/C
pressure dependence) that is run through the motor
torque model (which you don't get to see or touch)
and this torque model gets whack once you put in any
kind of serious cam. Also known as "A/C cruise control
effect".
The more wrong your VE table is at the low end, the
worse it gets, and so does your fueling, which makes
the motor respond slow to step-air and overshoot the
RPM target.
The A/C error is probably responsible for your hanging
idle, not the cracker (which goes to zero when stopped).
All you want from the cracker is to make a "soft landing"
so the idle RPM loop is no more challenged than it has
to be. Rich low end mixture from falsely high VE table
values post-cam, is the main problem. Not only makes
it fat, but (falsely) raises g/cyl lowering delivered spark.
Both bad for "catching your fall".
If you fix the VE table your torque model will become
more accurate (not entirely, but some) and the A/C
added will become less.
Not necessarily "big" (lift), but high overlap (which
follows high duration) cams are the worst for how low
end VE is depressed. See if you can find a well-proven
/ well-regarded tune file for a 6.0 with a setup that
matches your cam, intake and exhaust and compare
to what you have in the table now.
compressor drag torque (see IAT dependence and A/C
pressure dependence) that is run through the motor
torque model (which you don't get to see or touch)
and this torque model gets whack once you put in any
kind of serious cam. Also known as "A/C cruise control
effect".
The more wrong your VE table is at the low end, the
worse it gets, and so does your fueling, which makes
the motor respond slow to step-air and overshoot the
RPM target.
The A/C error is probably responsible for your hanging
idle, not the cracker (which goes to zero when stopped).
All you want from the cracker is to make a "soft landing"
so the idle RPM loop is no more challenged than it has
to be. Rich low end mixture from falsely high VE table
values post-cam, is the main problem. Not only makes
it fat, but (falsely) raises g/cyl lowering delivered spark.
Both bad for "catching your fall".
If you fix the VE table your torque model will become
more accurate (not entirely, but some) and the A/C
added will become less.
Not necessarily "big" (lift), but high overlap (which
follows high duration) cams are the worst for how low
end VE is depressed. See if you can find a well-proven
/ well-regarded tune file for a 6.0 with a setup that
matches your cam, intake and exhaust and compare
to what you have in the table now.
04-21-2017, 11:01 PM
#5
Yep, reduce the A/C Torque value.
Also, if you zero out cracker, your base airflow better be damn close.
With a big stall, I zeroed out cracker. I rely on follower and base airflow to control the IAC. I was able to reduce A/C airflow - mainly cuz it was causing bucking at low RPM when I let off the throttle.
Also, if you zero out cracker, your base airflow better be damn close.
With a big stall, I zeroed out cracker. I rely on follower and base airflow to control the IAC. I was able to reduce A/C airflow - mainly cuz it was causing bucking at low RPM when I let off the throttle.
04-22-2017, 08:52 PM
#6
A/C imposes an airflow adder based on a guesstimate of
compressor drag torque (see IAT dependence and A/C
pressure dependence) that is run through the motor
torque model (which you don't get to see or touch)
and this torque model gets whack once you put in any
kind of serious cam. Also known as "A/C cruise control
effect".
The more wrong your VE table is at the low end, the
worse it gets, and so does your fueling, which makes
the motor respond slow to step-air and overshoot the
RPM target.
The A/C error is probably responsible for your hanging
idle, not the cracker (which goes to zero when stopped).
All you want from the cracker is to make a "soft landing"
so the idle RPM loop is no more challenged than it has
to be. Rich low end mixture from falsely high VE table
values post-cam, is the main problem. Not only makes
it fat, but (falsely) raises g/cyl lowering delivered spark.
Both bad for "catching your fall".
If you fix the VE table your torque model will become
more accurate (not entirely, but some) and the A/C
added will become less.
Not necessarily "big" (lift), but high overlap (which
follows high duration) cams are the worst for how low
end VE is depressed. See if you can find a well-proven
/ well-regarded tune file for a 6.0 with a setup that
matches your cam, intake and exhaust and compare
to what you have in the table now.
compressor drag torque (see IAT dependence and A/C
pressure dependence) that is run through the motor
torque model (which you don't get to see or touch)
and this torque model gets whack once you put in any
kind of serious cam. Also known as "A/C cruise control
effect".
The more wrong your VE table is at the low end, the
worse it gets, and so does your fueling, which makes
the motor respond slow to step-air and overshoot the
RPM target.
The A/C error is probably responsible for your hanging
idle, not the cracker (which goes to zero when stopped).
All you want from the cracker is to make a "soft landing"
so the idle RPM loop is no more challenged than it has
to be. Rich low end mixture from falsely high VE table
values post-cam, is the main problem. Not only makes
it fat, but (falsely) raises g/cyl lowering delivered spark.
Both bad for "catching your fall".
If you fix the VE table your torque model will become
more accurate (not entirely, but some) and the A/C
added will become less.
Not necessarily "big" (lift), but high overlap (which
follows high duration) cams are the worst for how low
end VE is depressed. See if you can find a well-proven
/ well-regarded tune file for a 6.0 with a setup that
matches your cam, intake and exhaust and compare
to what you have in the table now.
Wow! I really appreciate your help! Thanks!!!
04-22-2017, 09:02 PM
#7
and you know what, my AC compressor isn't compressing the freon good enough (pressures are not what they should be) - So I wonder if the load on the engine isn't as much as it should be, since it isn't compressing as it should (it still gets cold while driving though, which is why it hasn't been replaced lol)
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07-11-2017, 08:19 AM
#8
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I see that this thread is a couple of month old but it really helps to set all of your Stall Saver values to zero. It gets in a bad loop when it keeps shutting off the compressor every time the idle dips.
07-13-2017, 09:07 PM
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Hope im not too confusing with my rambling lol
07-14-2017, 07:51 AM
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Could be. Are you cammed? I find that stall saver over corrects idle dips. idle trims and timing do a better job of catching idle dips and when stall saver engages, it disables idle trims for long enough for idle instability and possible stalling.
If idle is set up perfectly, then it won't matter if stall saver is disabled or not because it'll never be engaged but I can't always get A/C idle and heavy transitions to be so stable that they never engage stall saver so I just always disable it.
If idle is set up perfectly, then it won't matter if stall saver is disabled or not because it'll never be engaged but I can't always get A/C idle and heavy transitions to be so stable that they never engage stall saver so I just always disable it.
07-14-2017, 09:11 AM
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With cracker disabled, you need more corrective air for undershoot conditions and you need to slow down the corrective air after an overshoot.
Have you tried enabling the cracker but zeroing out the entire cracker table? That will keep it from going into adaptive idle without adding additional commanded air.
If you have tried that already, Try this -- double the proportional idle air low table and halve the proportional Air high table.
Have you tried enabling the cracker but zeroing out the entire cracker table? That will keep it from going into adaptive idle without adding additional commanded air.
If you have tried that already, Try this -- double the proportional idle air low table and halve the proportional Air high table.
07-14-2017, 09:36 PM
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Could be. Are you cammed? I find that stall saver over corrects idle dips. idle trims and timing do a better job of catching idle dips and when stall saver engages, it disables idle trims for long enough for idle instability and possible stalling.
If idle is set up perfectly, then it won't matter if stall saver is disabled or not because it'll never be engaged but I can't always get A/C idle and heavy transitions to be so stable that they never engage stall saver so I just always disable it.
If idle is set up perfectly, then it won't matter if stall saver is disabled or not because it'll never be engaged but I can't always get A/C idle and heavy transitions to be so stable that they never engage stall saver so I just always disable it.
07-14-2017, 09:41 PM
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With cracker disabled, you need more corrective air for undershoot conditions and you need to slow down the corrective air after an overshoot.
Have you tried enabling the cracker but zeroing out the entire cracker table? That will keep it from going into adaptive idle without adding additional commanded air.
If you have tried that already, Try this -- double the proportional idle air low table and halve the proportional Air high table.
Have you tried enabling the cracker but zeroing out the entire cracker table? That will keep it from going into adaptive idle without adding additional commanded air.
If you have tried that already, Try this -- double the proportional idle air low table and halve the proportional Air high table.
07-15-2017, 02:22 PM
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Originally Posted by Cb2417
maybe throttle cracker is the problem. My A/C is only on for a month or two a year as my car is a Canadian 6 month a year tops car. Half of these months are nice and chilly and require no a/c lol. I am more concerned with the irratic idle at hot starts and when I use the power steering. Other than this she runs great. Cold starts are stumble free and she sounds sexy!
07-15-2017, 08:32 PM
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I double the idle low proportional and that seemed to help but not totally eliminate the low rpm power steering stumble. Might increase it in small increments until it goes away completely. I increased my ac offset and the thing still stalls when ac is on and coming to a stop. It runs but just barely while at a stand still. Car is an m6 FWIW
07-16-2017, 09:55 PM
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Yeah for AC I bump the idle speed and commanded air on mine because the cam. It also helps to cut the idle proportional high values way down. Mine are 1/10 stock so it very gently settles down into idle.
Iirc the AC offset works in both directions. So might try reducing it vs increasing it
Iirc the AC offset works in both directions. So might try reducing it vs increasing it
07-22-2017, 12:03 PM
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Yeah for AC I bump the idle speed and commanded air on mine because the cam. It also helps to cut the idle proportional high values way down. Mine are 1/10 stock so it very gently settles down into idle.
Iirc the AC offset works in both directions. So might try reducing it vs increasing it
Iirc the AC offset works in both directions. So might try reducing it vs increasing it
07-22-2017, 09:28 PM
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Well I didn't try reducing AC offset max/min values from stock tune yet but I did double my airflow low in gear a/c on and off. Also I made my airflow high in gear A/C on and off 3/10 of what stock values are. I might try reducing them further.
The car idles fine with AC on while at a stand still. Hunts a bit but then stabilizes nicely. As soon as I take off at a light and go to stop at the next light it stalls (as it goes from say 2000 rpm and 30mph to a stop)
At least I can use the AC while I'm driving and the rpm's are up lol!
07-23-2017, 09:22 AM
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I'd set the min AC off in gear to -0.5. That'll keep it from learning a long term insanely low value.
Beyond that you're doing it right. Its iterative. You make small changes until you find what the car likes.
Beyond that you're doing it right. Its iterative. You make small changes until you find what the car likes.