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Yes but then you cannot run as much adaptive spark. At idle, peak tq is at 33. If you run something like 28, you can only run six degrees of adaptive spark which is not enough to catch undershoot when you take moi off the crank. I mean you CAN run more, but if you add 12 degrees to 28, you LOSE torque but the controller does not know that so it undershoots worse. So by running 18 idle timing I can use 14 degrees of adaptive spark.
With a heavy clutch and flywheel you can get away with increased base spark and less adaptive. When you cut moi, you need the more aggressive adaptive spark.
Interesting. I would have thought if you were closer to peak torque and a similar base/main timing it would have less undershoot, so it wouldn't matter as much that you had less adaptive spark control. Everything I've tuned including some healthy overlap cams liked more idle timing and close base/main tables, but almost all did not have a feather weight clutch/flywheel.
Interesting. I would have thought if you were closer to peak torque and a similar base/main timing it would have less undershoot, so it wouldn't matter as much that you had less adaptive spark control. Everything I've tuned including some healthy overlap cams liked more idle timing and close base/main tables, but almost all did not have a feather weight clutch/flywheel.
Believe it or not, a light clutch can be harder to tune than a massive cam. Then combine them...
Interesting. I would have thought if you were closer to peak torque and a similar base/main timing it would have less undershoot, so it wouldn't matter as much that you had less adaptive spark control. Everything I've tuned including some healthy overlap cams liked more idle timing and close base/main tables, but almost all did not have a feather weight clutch/flywheel.
The problem isnt undershoot, its the opposite. The timing the cpu tries to feed it if your base is super high will overshoot the idle, because it's trying to correct like you had the huge mass on the flywheel, then you get surge. Up, down, up, down, up, down, dead. I also run 18 degrees in the idle cell, though I don't run quite as much adaptive spark as he does. (1-2 degrees less, depending). I run more cracker and follower air, though, and the idle settles very smoothly on its own.
The problem isnt undershoot, its the opposite. The timing the cpu tries to feed it if your base is super high will overshoot the idle, because it's trying to correct like you had the huge mass on the flywheel, then you get surge. Up, down, up, down, up, down, dead. I also run 18 degrees in the idle cell, though I don't run quite as much adaptive spark as he does. (1-2 degrees less, depending). I run more cracker and follower air, though, and the idle settles very smoothly on its own.
You have a lightweight clutch/flywheel too don't you? When I said undershoot I was talking about idle, not spark. I'm with you that overshooting on timing (past MBT) will cause an undershoot in rpm due to the torque loss. Interesting stuff. Should create a thread in the PCM section with a tutorial specifically for dealing with this type of setup since it seems very specific in how to handle tuning it.
You have a lightweight clutch/flywheel too don't you? When I said undershoot I was talking about idle, not spark. I'm with you that overshooting on timing (past MBT) will cause an undershoot in rpm due to the torque loss. Interesting stuff. Should create a thread in the PCM section with a tutorial specifically for dealing with this type of setup since it seems very specific in how to handle tuning it.
Yes, I was talking about idle too - but with a lightweight clutch/fly package spark and idle under/overshoot can be quite closely related. For example an idle 250rpm undershooting might be fixed back up 250rpm with a 50# package hanging off the motor, but with a 22# package that same idle fix/correction may cause it to shoot up 600 rpm because the timing or air it was given overshot the mark, since it takes less to move now. Make sense? We need to make more, faster, smaller corrections.
By that same token, tables made for a lightweight combo might not work as well on a heavy package, because they may not correct enough.
The problem isnt undershoot, its the opposite. The timing the cpu tries to feed it if your base is super high will overshoot the idle, because it's trying to correct like you had the huge mass on the flywheel, then you get surge. Up, down, up, down, up, down, dead. I also run 18 degrees in the idle cell, though I don't run quite as much adaptive spark as he does. (1-2 degrees less, depending). I run more cracker and follower air, though, and the idle settles very smoothly on its own.
One of the other things I like to do is greatly increase the rpm low proportional air, and greatly decrease the proportional high rpm air. This way, when it goes into idle, it subtracts air very slowly from the airflow, and this sets it down gently. if it undershoots, it gets plenty of corrective air. I basically run a dead band of +/- 80 rpm, during which I rely on the adaptive spark with only very minor air corrections. it really kicks in at about 150 rpm error.
My logic is basically this: Idle typically consumes approx 10 g/sec at 1000 rpm idle. So once I get to 100 rpm error, the car should need approx 1 g/sec. So I use 0.8 g/sec per 100 rpm error, except in the dead band. The other 0.2 g/sec I put in the integral table. Those are both in the rpm low areas. In the RPM high areas, I run something between 10% and 25% of factory, so it pulls air out very slowly.
This was how I was able to get it to settle down with throttle stabs in the garage, car not moving. No cracker when the car isn't moving.
I have also found that these settings work on heavy (stock or worse) flywheels also. The larger MOI makes the engine so much less responsive to the commanded changes that the ECU has plenty of time to react. When the clutch is light, it's almost like the engine reacts faster than the IAC motor.
The other thing I do is zero out the derivative from 0 to 0.05. An overactive derivative can take a stable idle and make it start oscillating all on its own. it helps keep the IAC motor from wandering around in response to minor cam surge.
I was initially thinking that my return-to-idle problems were due to the cam, and was trying to fix it mostly with airflow-related changes (cracker, follower, etc). I got it about 95% fixed but it was still dying every once in a rare while.
But after some posts in the RPS clutch thread and a couple messages with Darth_V8R I figured that I might have been barking up the wrong tree.. So last week I zero'd out the cracker and follower tables and started over with the assumption that this problem stems from having a lighter clutch, and should be tackled primarily with PID tuning... And it's about 95% fixed again.
I'm about to start combining some airflow tweaks with the PID tweaks to see if that makes it 100%.
I can't help but wonder if the OP also did something to reduce the MOI of whatever is attached to his crankshaft, and how much that contributes to his car's return-to-idle problem.
Today I turned the integral down another notch and then just cranked up the derivative gains until it stopped overshooting idle RPM on the way down. Well it almost stopped - it stumbled on the way into my garage when I got back home, so there's at least one more iteration coming. But it almost never undershoots the target RPM far enough to hit the anti-stall behavior anymore, it just drops right to idle, from any RPM. I think I'm going to have this fixed without using any follower or cracker.
In my last tuning session I turned up the derivative so far it would waver on the way to back down to idle, and still hit the stall saver once in a while. So I backed off a little bit on the D term and figured I'd have to put some cracker/follower back in after all. So that was today's experiment. I got through a test drive without bouncing off the stall saver, so I think I'm in the home stretch now. It's returning to idle a bit more slowly than stock now, so the next round will be turning up the decay and/or turning down the extra airflow to find the balance between quick return and overshooting.
It also occurred to me (embarrassingly late...) that the the cam really is a big factor in my return-to-idle problem. It's not entirely the clutch because the clutch was installed a few months before the cam, without tuning, and it still drove fine. The stock tune can cope with the light clutch alone, driveability just turned to crap when the cam went in. But retuning the PID tables for a lighter clutch makes perfect sense, and it's definitely a pre-requisite for getting the combo to work right.
Try taking even more out of your proportional high rpm correction. Maybe even zero up to 150 error. That last drop would then be integral only and settle down very gently.
You can always add more correction to get it to fall faster. Hanging it a bit can help you work out settling speed. Then keep increasing until it starts to undershoot.
In my own car I have 1/10 the proportional over speed air as under speed. Maybe not an exact tenth but a very high ratio difference. I want lots of supporting air low and very little correction high.
Derivative air, I would zero out until .05. Then use 2 for the rest of it. That will help stabilize the iac when you are close to idle speed but still be very reactive when large transitions occur.
I don't think the P/N tables come into play on my car. It's manual, and the P/N columns were all zero in the stock tune. I tried copying the in-gear values into them and nothing changed, so I just put them back to zero. With half as many values to tweak, I can tune twice as fast.
03-23-2020, 06:09 AM
