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Old 06-24-2012, 04:49 PM   #1
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Default Dashpot decay factor? Can't find info the manual

I've got a Reverant built MS2 running great on my MSM. I had one tiny issue with a idle droop when coming to stop signs.

I did 2 things to try to solve the issue, increased Min Duty for PID % from 18 to 20, and added 5% to Dashpot adder %.

Now when coming to a stop, the car hangs the idle at around 1050. It takes probably 5-6 seconds to settle from there to my target of 850. This is significantly less annoying than having it droop to 500, scaring the crap out of me like its going to stall (although it never does), and then coming back up to the target of 850.

I'd just stop here if I could leave well enough alone, but I can't. I can't figure out what "Dashpot decay factor" is. I can't locate a reference to it in any manual and i'm not sure how to begin adjusting it. I can find "Dashpot decay rate", but I don't know if that's the same thing or not. I suspect it could improve/reduce the amount of time that the idle now hangs when coming to a stop. Anyone have any info on this, what it does, and what a good starting point would be?

THANKS!

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Old 06-24-2012, 05:00 PM   #2
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Dashpot Adder takes the last known value for your PWM output and adds that % to it when getting back into CL idle. So say you had been idling at 32% PWM output, the next time it comes in it will automatically go to 37%. This is why your idle is high.


Edit: You already know this. Nevermind. I don't know how to work the decay. Sorry!
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Old 06-24-2012, 05:03 PM   #3
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Yes, I found a lot of information on the Dashpot adder. My idle isn't high once it settles, it just takes too long to settle now. Adding 5% dashpot did exactly what I read it would do, and solved my idle droop.
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Old 06-24-2012, 06:53 PM   #4
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5% is pretty high, I use like 2%. i bet you're going lean as you come down to idle and why you need so much.

the decay is how long it stays at your dashpot number before it comes down to the last value; I use 0 for that.

Also make sure your CL delay isn't very long I use 2.
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Old 06-24-2012, 08:23 PM   #5
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5% was just want I plugged in to start with, I may have to go down from there. I'll also check my AFRs more closely returning to idle and adjust if needed. I'll need to turn my overrun off to see whats going on there.

My CL delay is also 2. I was noticing the dip just before CL kicked in. It didn't last long as CL fixed it after 2 seconds.

I was worried that 0 for the decay factor would do something odd like never decay. I'll keep messing with it, I think i'm on the right track. Thanks for confirming.
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Old 06-25-2012, 10:48 AM   #6
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For anyone else looking, I did end up finding the documentation that explains this feature and more. The PDF is in the first post of this thread: http://www.msextra.com/forums/viewto...p?f=91&t=43793
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Old 06-25-2012, 10:50 AM   #7
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Quote:
Originally Posted by msm782 View Post
5% was just want I plugged in to start with, I may have to go down from there. I'll also check my AFRs more closely returning to idle and adjust if needed. I'll need to turn my overrun off to see whats going on there.

My CL delay is also 2. I was noticing the dip just before CL kicked in. It didn't last long as CL fixed it after 2 seconds.
yeah, so really look at logs as you're coming back into idle, see what the AFRs are, see if you are injecting fuel too late and there's a delay coming back from overrun or something. I remember setting my overrun to return fuel at 1200RPM once, I had a bad dip as I came back to idle. After going over logs I could see that from the moment I injected fuel again, to the point where the AFRs would register on the log, was enough delay to cause the idle to dip as the fuel wasnt injected fast enough. I moved that value up to 1500RPM and the fuel got there in time to stabilze and the dip went away.

AFRs and timing really effect idle speed, so make sure that's kosher so things are stable before you go into CL idle.

Last edited by Braineack; 06-25-2012 at 11:34 AM.
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Old 06-25-2012, 11:14 AM   #8
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Thanks for posting this.
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Old 07-03-2012, 03:44 PM   #9
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I did this my settings and now whenever I touch my gas pedal and rev the engine, it just kinda stays up there for a while. Maybe a few seconds before starting to come back down.
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Old 07-03-2012, 03:50 PM   #10
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Decrease the dashpot adder.
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Old 07-03-2012, 04:52 PM   #11
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I've solved most of my issue by adjusting overrun to return fuel earlier (Thanks brain). This allowed me to bring my Dashpot down from the 5% I had originally to 2%. Also changed decay factor to 1. Its now perfect/stock-like.

Now I just need to work on getting my throttle blips while rev-matching as crisp as I'd like. I cleaned up the bottom of my VE table and that helped a lot, but its still not perfect. I'm guessing I need to mess with AE next?
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