Why is my Dashpot not working?
#1
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I posted this question on MSExtra and have been immensely diss-appointed in the lack of responses
As far as I can tell this looks like a bug to me - though it could just as readily be a tuning issue. For the life of me, if it is, I've absolutely no idea how to fix it.
I had hoped the devs might have taken a look at it, I'm not really sure how much more evidence - logs etc - I can post up.
Anyway I digress, here is my issue in a sort of copy/paste from MSEXTRA.
If anyone can offer any advise as to why this is happening I'd be most grateful:
Here is my car in Closed loop, the Idle PWM duty is 33.3
![](https://www.miataturbo.net/attachments/megasquirt-18/69983-why-my-dashpot-not-working-graph1.png?dateline=1363178143)
Here is my car about to enter an idle state, note that the Idle PWM duty is at 29.4, as you can see in the graph, this causes a nasty idle dip.
![](https://www.miataturbo.net/attachments/megasquirt-18/69984-why-my-dashpot-not-working-graph2.png?dateline=1363178143)
My dashpot is set at 3.9
33.9 - 29.4 = 3.9
Looks like my dashpot being subtracted and not added
My log and .msq are below, apologies in advance for the size of the log (13Mb) I tried to truncate it, but it just became unreadable.
Log
http://dl.dropbox.com/u/16897858/Meg...7_07.35.44.msl
.msq
http://dl.dropbox.com/u/16897858/Meg...7_08.47.41.msq
Then I upgraded to the latest 1.2 release code and changed PID activation to include VSS - so it wasn't accidentally driven down when not stationary and saw no change
Idle PWM is 29.8 VSS is 0, CL is active
![](https://www.miataturbo.net/attachments/megasquirt-18/69985-why-my-dashpot-not-working-idle1.png?dateline=1363178143)
Next set of lights, Idle PWM is slightly lower at 29.4, predictably there is an idle dip, where's the Dashpot adder gone? Surely the idle valve should be at 33.7%?!?
![](https://www.miataturbo.net/attachments/megasquirt-18/69986-why-my-dashpot-not-working-idle2.png?dateline=1363178143)
Another example
![](https://www.miataturbo.net/attachments/megasquirt-18/69987-why-my-dashpot-not-working-idle3.png?dateline=1363178143)
Note the dip isn't severe here, but still annoying, also look at the Idle valve before I come to a stop, it spikes and then drops it's value for no reason?
![](https://www.miataturbo.net/attachments/megasquirt-18/69988-why-my-dashpot-not-working-idle4.png?dateline=1363178143)
However, the dashpot does seem to work but only when you don't move the car, here is me blipping the throttle, the idle valve reacts as you'd expect.
![](https://www.miataturbo.net/attachments/megasquirt-18/69989-why-my-dashpot-not-working-works%2520when%2520blipping.png?dateline=1363178143)
Below are my current .msq and my log that the above images are taken from.
http://dl.dropbox.com/u/16897858/Meg...urrentTune.msq
http://dl.dropbox.com/u/16897858/Meg...8_07.38.16.msl
And finally today I managed to grab an SDCard log of the event
![](https://www.miataturbo.net/attachments/megasquirt-18/69990-why-my-dashpot-not-working-nodashpot.png?dateline=1363178143)
SDCard Datalog, look around the 155.576 timestamp
http://dl.dropbox.com/u/16897858/Meg...12_LOG0035.msl
Dashpot is not being added, or it is and then a whole chunk of duty is whacked off way before I get close to idle RPM's. Either way it's messing up my idle and I see no reason in my tune as to why it's happening.
TL : DR Why the chuffy chuff is Dashpot not being added in my tune?
As far as I can tell this looks like a bug to me - though it could just as readily be a tuning issue. For the life of me, if it is, I've absolutely no idea how to fix it.
I had hoped the devs might have taken a look at it, I'm not really sure how much more evidence - logs etc - I can post up.
Anyway I digress, here is my issue in a sort of copy/paste from MSEXTRA.
If anyone can offer any advise as to why this is happening I'd be most grateful:
Here is my car in Closed loop, the Idle PWM duty is 33.3
![](https://www.miataturbo.net/attachments/megasquirt-18/69983-why-my-dashpot-not-working-graph1.png?dateline=1363178143)
Here is my car about to enter an idle state, note that the Idle PWM duty is at 29.4, as you can see in the graph, this causes a nasty idle dip.
![](https://www.miataturbo.net/attachments/megasquirt-18/69984-why-my-dashpot-not-working-graph2.png?dateline=1363178143)
My dashpot is set at 3.9
33.9 - 29.4 = 3.9
Looks like my dashpot being subtracted and not added
My log and .msq are below, apologies in advance for the size of the log (13Mb) I tried to truncate it, but it just became unreadable.
Log
http://dl.dropbox.com/u/16897858/Meg...7_07.35.44.msl
.msq
http://dl.dropbox.com/u/16897858/Meg...7_08.47.41.msq
Then I upgraded to the latest 1.2 release code and changed PID activation to include VSS - so it wasn't accidentally driven down when not stationary and saw no change
Idle PWM is 29.8 VSS is 0, CL is active
![](https://www.miataturbo.net/attachments/megasquirt-18/69985-why-my-dashpot-not-working-idle1.png?dateline=1363178143)
Next set of lights, Idle PWM is slightly lower at 29.4, predictably there is an idle dip, where's the Dashpot adder gone? Surely the idle valve should be at 33.7%?!?
![](https://www.miataturbo.net/attachments/megasquirt-18/69986-why-my-dashpot-not-working-idle2.png?dateline=1363178143)
Another example
![](https://www.miataturbo.net/attachments/megasquirt-18/69987-why-my-dashpot-not-working-idle3.png?dateline=1363178143)
Note the dip isn't severe here, but still annoying, also look at the Idle valve before I come to a stop, it spikes and then drops it's value for no reason?
![](https://www.miataturbo.net/attachments/megasquirt-18/69988-why-my-dashpot-not-working-idle4.png?dateline=1363178143)
However, the dashpot does seem to work but only when you don't move the car, here is me blipping the throttle, the idle valve reacts as you'd expect.
![](https://www.miataturbo.net/attachments/megasquirt-18/69989-why-my-dashpot-not-working-works%2520when%2520blipping.png?dateline=1363178143)
Below are my current .msq and my log that the above images are taken from.
http://dl.dropbox.com/u/16897858/Meg...urrentTune.msq
http://dl.dropbox.com/u/16897858/Meg...8_07.38.16.msl
And finally today I managed to grab an SDCard log of the event
![](https://www.miataturbo.net/attachments/megasquirt-18/69990-why-my-dashpot-not-working-nodashpot.png?dateline=1363178143)
SDCard Datalog, look around the 155.576 timestamp
http://dl.dropbox.com/u/16897858/Meg...12_LOG0035.msl
Dashpot is not being added, or it is and then a whole chunk of duty is whacked off way before I get close to idle RPM's. Either way it's messing up my idle and I see no reason in my tune as to why it's happening.
TL : DR Why the chuffy chuff is Dashpot not being added in my tune?
#3
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This is something I also thought I would be experiencing for quite a while. Everytime I came to a red light or something like this the car will go into closed loop idle and drop instantly to the target idle. (and lower if lights, fan, etc. are on at this moment)
With the new "initial value table" I worked my way around this by adding some percent to my initial values, so that the starting point for the idle is a bit higher anyway...
I am also closely fooling your thread at msextra.com - hopefully James will take some time to look this up...
@Brain - I had this on all of the latest firmwares (also the alpha ones)
Here is a random screenshot - car going to idle - no adder whatsoever...
With the new "initial value table" I worked my way around this by adding some percent to my initial values, so that the starting point for the idle is a bit higher anyway...
I am also closely fooling your thread at msextra.com - hopefully James will take some time to look this up...
@Brain - I had this on all of the latest firmwares (also the alpha ones)
Here is a random screenshot - car going to idle - no adder whatsoever...
![](https://www.miataturbo.net/attachments/megasquirt-18/70028-why-my-dashpot-not-working-idle_no_adder.jpg?dateline=1363180518)
#6
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This is something I also thought I would be experiencing for quite a while. Everytime I came to a red light or something like this the car will go into closed loop idle and drop instantly to the target idle. (and lower if lights, fan, etc. are on at this moment)
With the new "initial value table" I worked my way around this by adding some percent to my initial values, so that the starting point for the idle is a bit higher anyway...
I am also closely fooling your thread at msextra.com - hopefully James will take some time to look this up...
@Brain - I had this on all of the latest firmwares (also the alpha ones)
Here is a random screenshot - car going to idle - no adder whatsoever...
![](https://www.miataturbo.net/attachments/megasquirt-18/70028-why-my-dashpot-not-working-idle_no_adder.jpg?dateline=1363180518)
With the new "initial value table" I worked my way around this by adding some percent to my initial values, so that the starting point for the idle is a bit higher anyway...
I am also closely fooling your thread at msextra.com - hopefully James will take some time to look this up...
@Brain - I had this on all of the latest firmwares (also the alpha ones)
Here is a random screenshot - car going to idle - no adder whatsoever...
![](https://www.miataturbo.net/attachments/megasquirt-18/70028-why-my-dashpot-not-working-idle_no_adder.jpg?dateline=1363180518)
![](https://www.miataturbo.net/images/smilies/smile.gif)
#7
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The initial values table is a completely broken strategy. It will only work for a car without any additional on/off loads (such as headlights, cabin fan, defroster, etc).
the voltage compenstation table should take care of the rest if you have shitty NA alternator.
it works much better, imho, than the last known value.
#9
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Are you both using VSS to activate PID? try turning that off, I don't quite understand why you'd want to use VSS anyways, that means if you throw it in nuetral and cost, it wont control the idle valve so long as youre at speed, but it should.
I have a feeling that's what's causing it and something y8s ran into long ago.
Also, use idle RPM timing correction! Why would you have that off given the ability to run it? and idle ve?!
I have a feeling that's what's causing it and something y8s ran into long ago.
Also, use idle RPM timing correction! Why would you have that off given the ability to run it? and idle ve?!
#11
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well that's why I said shitty NA alt. I much prefer intial values over last know. I dont have an issue when my fan is going (i dont even use adder with it on), or defroster, only the headlights and I've tuned the voltage curve to compensate for that.
#12
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Are you both using VSS to activate PID? try turning that off, I don't quite understand why you'd want to use VSS anyways, that means if you throw it in nuetral and cost, it wont control the idle valve so long as youre at speed, but it should.
I have a feeling that's what's causing it and something y8s ran into long ago.
Also, use idle RPM timing correction! Why would you have that off given the ability to run it? and idle ve?!
I have a feeling that's what's causing it and something y8s ran into long ago.
Also, use idle RPM timing correction! Why would you have that off given the ability to run it? and idle ve?!
(P.S.: I have a very light 1.6 Fidanza flywheel if that matters...)
@richyvrlimited
Done!
#13
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We both argeed that there should be idle control in nuetral when coasting, he disagreed. I believe y8s quickly stopped using the VSS PID activation feature when it was apparent it was more trouble than worth.
I'm on 1.2.0pro and dont believe I have the dashpot issue, only on like beta18-24 where it was broken. But I've only driven the car 30 seconds since I installed the ms3pro, but my dad would have complained of idle droop without the dashpot because it was pretty bad when the feature wasn't working.
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Also, use idle RPM timing correction! Why would you have that off given the ability to run it? and idle ve?!
![wink](https://www.miataturbo.net/images/smilies/wink.gif)
EDIT: If you look at the last SD card log the idle valve does weird ****. as soon as the throttle goes to below the threshold the idle valve PWM %increases and looks to include the dashpot. But only for a split second, and then it drops - massively - to some arbitrary number that bears no relation to a last known good value.
RE: the initial values table. That would be handy for me during warmup, (ignore my signature I have a coldside supercharger with no IC now which means IAT's rise quickly so unless I stop every 30 seconds the initial value is way off until the car is fully warmed up). After that it's as Rev says pretty useless.
@Zaphod, thanks!