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Tuning boost control on the MS3x

Old 05-05-2014, 06:52 PM
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Default Tuning boost control on the MS3x

I've got the DIY solenoid. I'm trying to tune open loop to a good ratio before I tune closed loop, but it seems like from day to day the thing just overshoots the targets I set on the previous day. And not by a small amount. IE, one day it will hold 10psi to redline the next day it will overboost to the fuel cutoff (around 15psi) by 4000rpm.

I was under the impression that conditions could make open loop vary, but I didn't think it was that much.

Or am I doing it wrong? I'm using slow and 39hz freq range with control interval at 20ms. These were all the defaults I think.
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Old 05-06-2014, 12:04 PM
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I'm wondering if this is just the vagaries of open loop tuning biting me in the ***. Not sure yet, but will test today by varying parameters. I was just so surprised at how much variance there was from one day to the next that I didn't consider that small parameter changes make a large difference in open loop tuning and so weather changes might affect it as well.
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Old 05-06-2014, 12:37 PM
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that's why we dont use open loop...
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Old 05-06-2014, 02:10 PM
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I wasn't really planning to use it, but everyone says you should dial in open loop to some degree before going to closed loop, that's really all I was trying to do. I guess I just didn't realize how oddly variable it could be.
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Old 05-06-2014, 02:14 PM
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so long as it's close to your target and stable throughout the revs, id turn on CL now.
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Old 05-06-2014, 04:28 PM
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Okay, so you're right. The open loop mode is just super sensitive to changes. I got in the car today, same overboosting. I dropped the values in my table down by 5 points across the top end, holds boost fine. I guess it just gets to a certain point and once it is over that threshold it's just sky is the limit.

I'll start doing CL tuning now as this open loop stuff is nutso.
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Old 05-06-2014, 04:36 PM
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Also the clutch slips over 10psi. Oh well, new one on the bench.
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Old 05-06-2014, 04:44 PM
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So, does it matter if I have lower values in the boost table being lower boost and higher values being higher boost?

On the Boost Control manual it seems to indicate that higher values should indicate higher duty for the solenoid and therefore lower boost.

Boost Control

Edit: Apparently it does? Since the thing indicates

NOTE: The output polarity setting only changes the actual duty on the output. Regardless of this setting, the boost control algorithm is designed to operate on the assumption that more duty = less boost.
Or does it just not give a crap what is in the open loop table? I'm thinking that's what it is, once you go CL it doesn't give a crap.

Last edited by Harv; 05-06-2014 at 04:57 PM.
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