MS2 Boost Control Tuning

[motomanmike]

Last week I got my board ready to run a solenoid to control boost through MS2.  I'm running a stock L28ET, 400cc injectors, stock turbo with an intercooler. 

 

I'm trying to tune the Open Loop

Solenoid is from DIY

 

Have the frequency set at 19.5hz as recommended by DIY

Have controller interval at 20ms

 

Inverted,

 

Closed duty=0

Open duty =100%

 

When I lower the duty boost increases as all the MS writes ups recommend.

 

What I can't get dialed in is the holding higher boost.  I want to run 10lbs.  My problem is no matter what I put in the Duty cycle map I either overshoot and hit the boost cut, or I don't make any more boost than stock.  Its like that initial spool I can't get it to react to bring it back in check and it over boosts. Granted i'm just now experimenting with this but I burnt about 10 gallons of fuel over the weekend trying to get it tuned somewhat to where I want. 

 

I've read the MS2 manual for setting it all up. I've trolled alot of forums, miata forums especially.  I've experimented with the closed loop but it has even more settings that affect eachother and everyone seems to lean towards tuning the open loop first.  I also experienced quite a bit of noise trying to use the closed loop.  Tunerstudio would almost pause, then regain speed, pause but only on open loop.

 

Anyone have some resources they can point me in the direction of that maybe would give a base line to start at?  Maybe a base duty cycle map for reference?

 

I appreciate any input you can give me

 

[BLOZ UP]

What gear are you trying this in? I recommend 4th or 5th for the most consistency. If your solenoid (and wastegate) can flow enough, you should be able to set the open loop duty cycle to a value that holds a certain boost level. If that's not working, you have a mechanical problem.

 

EDIT: Also try a 15 or 10 ms control interval.

Edited October 22, 2013 by BLOZ UP

[motomanmike]

I've been doing 4th gear pulls from about 3500rpm. I got it to hit my desired mark (165kpa) on my way home from work and it was consistent but it won't hold it. Just falls back to stock (wastegate spring boost around 145kpa) Making changes trying to compensate for the sag I get just boost runaway is the best way to describe it, it climbs very fast almost like the wastegate stuck shut. I know the wastegate isn't stuck it moves freely no bind but it might be a bad actuator maybe? I'm going to heed your advice because ms seems to be doing what it should other than tunerstudio acting up on closed loop. Thanks for the reply.

[BLOZ UP]

acting up on closed loop? I thought you were trying to get a set duty cycle to work in open loop? Closed loop involves tuning the PID loop, which is harder.

[motomanmike]

Yeah I didn't do much on closed loop. I tried to see if it worked over the weekend but have focused totally on open loop duty cycles.

[winstonusmc]

Here is my setup on MS3, should be similar on MS2. It gives me about 13psi. I also calculated the boost curve vs duty in an excel graph. This is with stock turbo and the DIY solenoid.

 

 

[BLOZ UP]

Try 10ms control interval with the same DC.

[motomanmike]

I'll probably get to work on it this coming weekend. Time is very limited during the week.  Bloz up i don't know where you find the time to do everything you build but i'd sure like to have some of it LOL.  I certainly enjoy the build threads.

[BLOZ UP]

Heh, I was at university and skimped on HW and studying. Now I have a 9-5 (8-6), and don't have a lot of time to work on it on the week either. Although I do usually keep a few tabs of car forums open while at work.

[motomanmike]

I swapped actuators tonight and all seems happy happy.  The old one had a rather notchy abrupt movement to it but wasn't leaking. I have my settings on closed loop now.  I got it working ok on open loop and switched over to closed loop.  I only hit the boost cut once tonight on a very aggressive run shifting from 3rd to 4th.  Otherwise it would spool up and hover right around 165kpa which is pretty close to what I want.  It doesn't roll on as fast as i'd like but its working right.  Also, i'm not sure whether it made the difference or not but the stock turbos have 2 ports on them that T into 1 port then runs to the actuator. I've blocked the lowest port on the turbo compressor housing and just have the top port going to the boost solenoid.  I changed alot at once but at least its to a point i can spend some time smoothing it out.  Thanks guys.

[BLOZ UP]

With open loop you can set your duty cycle to 100% open (in other words, maximum boost) in the areas where full boost is not physically possible, to help spool up. For closed loop, you can increase the proportional gain, but it's less straightforward.

[motomanmike]

I'm having a little better luck with the closed loop. I drove the car probably 2 hours today and it is responding well and man I see why people let turing the dial up get the best of them. With the additional  boost this thing rips pretty good.  I actually like that the boost  rolls on later.  It drives pretty much like an NA car until I roll into it pretty hard and seems to be cycling the turbo less. I'll keep playing with it but i'm certainly glad the inputs i'm making are controllable and not feeling like the rear is going to fall out on the highway from the boost cut hitting, It holds at target the whole time on spirited runs.  I'll just keep playing with how fast I like it to get there.