Tuning Boost Control With Bias Table

Testing and development of Megasquirt 3

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Dennis930
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Re: Tuning Boost Control With Bias Table

Post by Dennis930 »

I have been tweaking on boost control on and off for while, but now I need some advice. The issue I have been having is that boost control will get to my boost target 217 KPA but when I shift gears and floor the pedal the boost comes up so quick I get overboost cut out (set at 228KPA). While in the basic mode, I have tried changine the slider from 150, to 225, to 250, to 325 and to 375. But i still got the overboost spike when shifting gears, or while @4000 RPM and flooring the pedal. Looking at the logs I did, it appears that the boost duty after the 40KPA delta is always higher than what is in the initial values table. So, I lowered the slider to 50 then to 24. The boost duty values are closer to the inial values table, but I still get overboost when shifting. Then I changed from basic to advanced and changed I and P terms to see if it made any difference, but I still get overboost when shifting.

So, I am looking for guidance. Do I need to lower I, increase P, or maybe increase overboost cut a little higher than 228KPA hoping PID will level the boost off after the spike. I am using a MAC valve @19.5 Hz. I have attached my msq and the last datalog. In the datalog, there is overboost cut @1645.422 and 2736.843 sec (as shown by status 2).
Porsche 930 3.0 Slantnose
MS3/MS3X Sequential Injection & Spark, MS Knock, Dual plug, LS2 coils, Siemens 55 lb/hr HiZ injectors, ALM-ADV Wide Band,
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muythaibxr
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Re: Tuning Boost Control With Bias Table

Post by muythaibxr »

Did you verify using open loop boost that you can control boost? Does more duty give more boost?
Megasquirt is not for use on pollution controlled vehicles. Any advice I give is for off road use only.
Dennis930
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Re: Tuning Boost Control With Bias Table

Post by Dennis930 »

I will go back to the set up mode to see if I get overboost when shifting gears at high RPM's. Yes, with increased duty, boost goes up. In my datalog, the first pull, the engine goes from about 2000 to 6000+ RPM's with no overboost (2nd gear). But when I shift to 3rd, apply WOT @4000+ RPM's, the boost climbs quickly and hits overboost.
Porsche 930 3.0 Slantnose
MS3/MS3X Sequential Injection & Spark, MS Knock, Dual plug, LS2 coils, Siemens 55 lb/hr HiZ injectors, ALM-ADV Wide Band,
Carrera Intake, Extrude honed, Ford 70mm Throttlebody, GTX3071R Turbo
muythaibxr
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Re: Tuning Boost Control With Bias Table

Post by muythaibxr »

That's not what I'm asking. I'm asking if you have either used open loop boost control or closed loop in "setup" mode without PID to confirm that you can control boost accurately and repeatably.

If you can't do that in open loop or in closed loop in setup mode, then you need to fix that first before trying to go to full closed loop.

Start with open loop, get that working right, and go from there.

Ken
Megasquirt is not for use on pollution controlled vehicles. Any advice I give is for off road use only.
aidandj
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Re: Tuning Boost Control With Bias Table

Post by aidandj »

muythaibxr wrote:Couldn't hurt to try... actually maybe go to advanced mode and turn off P and D terms temporarily. As long as you're willing to experiment and overboost protection is working for you. In other words don't do it unless you're fairly confident that you won't pop your engine. So you'd want 0,100,0 for P, I, and D respectively (defaults in basic mode are 100,100,100).

You could potentially reduce the lower limit delta too so you're not so far from the target when PID engages.

Ken
Ken, in 1.5.1 alphas is 100,100,100 still the default PID in basic mode?

So tuning advance mode would be start in basic, get it close with the slider. Then switch to advance mode, set all terms to 100, and adjust from there.

Add I to remove oscillations?
Add P to get to the target faster?
Add D to smooth things out?

Or should we start at something like all 0s and adjust from there?
elaw
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Re: Tuning Boost Control With Bias Table

Post by elaw »

aidandj wrote:Ken, in 1.5.1 alphas is 100,100,100 still the default PID in basic mode?
I'd love to know the answer to this too!

I've got my setup working okay in basic mode but think it could use more D and less I. But rather than lose the work I've done, I'd like to start with settings that are as close to the current ones as possible when I switch to advanced mode.
Eric Law
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jsmcortina
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Re: Tuning Boost Control With Bias Table

Post by jsmcortina »

P=I=D=100 in Basic mode yes.

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elaw
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Re: Tuning Boost Control With Bias Table

Post by elaw »

Fantastic, thanks!

That provides more adjustment than I thought there was... right now the grayed-out boxes for PID are showing 12, 12, and 175 and I thought those might be the values in use.
Eric Law
1990 Audi 80 quattro with AAN turbo engine: happily running on MS3+MS3X
2012 Audi A4 quattro, desperately in need of tweaking

Be alert! America needs more lerts.
muythaibxr
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Re: Tuning Boost Control With Bias Table

Post by muythaibxr »

aidandj wrote:
muythaibxr wrote:Couldn't hurt to try... actually maybe go to advanced mode and turn off P and D terms temporarily. As long as you're willing to experiment and overboost protection is working for you. In other words don't do it unless you're fairly confident that you won't pop your engine. So you'd want 0,100,0 for P, I, and D respectively (defaults in basic mode are 100,100,100).

You could potentially reduce the lower limit delta too so you're not so far from the target when PID engages.

Ken
Ken, in 1.5.1 alphas is 100,100,100 still the default PID in basic mode?

So tuning advance mode would be start in basic, get it close with the slider. Then switch to advance mode, set all terms to 100, and adjust from there.

Add I to remove oscillations?
Add P to get to the target faster?
Add D to smooth things out?

Or should we start at something like all 0s and adjust from there?
It is all 100s by default. I should be used to get you to target, P to tune for changes in set point or changes in boost, D to slow down correction based on rate of change.
Megasquirt is not for use on pollution controlled vehicles. Any advice I give is for off road use only.
suberimakuri
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Re: Tuning Boost Control With Bias Table

Post by suberimakuri »

FWIW: 11kpa overboost is not much tolerance, especially when you're already boosting to 217kpa. Factory cars that I've owned run 4-5+ psi overboost cuts.
Dennis930
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Re: Tuning Boost Control With Bias Table

Post by Dennis930 »

Yes, I increased overboost from 228 to 235kpa. I also changed from a 4 port MAC (plumbed as 3 port) to a high frequency MAC (35hz) and removed the vent muffler. The Porsche wastegate dome is a rather large volume compared to most, so venting it quickly through 1/4" hose is a challenge. These changes fixed the boost spike when shifting from 2nd @6500 RPM to 3rd (approx. 4400 RPM) at WOT.
Porsche 930 3.0 Slantnose
MS3/MS3X Sequential Injection & Spark, MS Knock, Dual plug, LS2 coils, Siemens 55 lb/hr HiZ injectors, ALM-ADV Wide Band,
Carrera Intake, Extrude honed, Ford 70mm Throttlebody, GTX3071R Turbo
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