I'm having some issues (I think) getting my closed loop boost control just right. I am targeting 15psi in my bias table at 100% TPS, the closed loop is over shooting that to 16psi (4800ish RPM) as it ramps up and then slowly falls off to about 13.8 by 7200. I've tried to increase bias up high, but short of making the target like 250kpa when i'm trying to get 205, it's not seeming to have an effect. I was hoping to get some knowledge on how people are tuning their closed loop. I did have the brilliant idea of using spring pressure for my peak boost and just using boost control for keeping the waste gate closed to build boost, but i dont run nearly this much boost on track days and I'm trying to avoid swapping out springs manually every time. I currently have a 5psi spring that runs to about 7psi of boost when there's no EBC involved. Thats what I run on track days.

If anyone has any good closed loop boost tuning resources and wants to post them instead of teaching me, that would be great as well!

 

Try this thread: https://www.miataturbo.net/megasquir...oop-ebc-94391/

 

100 miles apart great minds think alike.

That 18PSI thread is a great resource. I'm having kind of the same issues ref. my thread below.

https://www.miataturbo.net/megasquir...6/#post1675389

 

Nice! I have the same boost building spike I'm trying to get rid of. That other link is a little over my head but I figure if I read it enough times and get back to my Miata to test it'll eventually sink in.

 

I never like to leave a post i make unfinished when i feel like i've successfully gotten to a point where i can contribute back to the forum. here's a quick brief on what I did: I've been fighting my boost control for a while — built to peak (16psi when my target was 15) then dropped to high 12s and slowly climbed back up. Running an MS3Pro, EFR 6258, 5 psi spring, single port boost controller. I was on basic closed loop with P/I/D all at 100. The sensitivity slider was weird and never seemed to really work to help. After messing with a PID simulator online, my best guess was that all three terms maxed simultaneously was causing the I term to overcorrect hard, drop boost, then slowly wind back up.

P responds to how far off target you are right now. Too high and you get fast oscillation, too low and boost never gets close. The harder you push P to get you to target, the more oscillations, its like you are constantly working against yourself, that's why I matters so much. I is what actually pulls boost to target and holds it there — P alone cannot reach setpoint, it always settles slightly below if you keep it conservative. If you go crazy with P it blows past target and oscillates wildly. D brakes the rate of change to prevent overshoot but on a noisy MAP signal it tends to cause more problems than it solves. I left it at zero and never needed it.

Before touching PID I tuned the bias table in open loop. In open loop there's no correction happening so boost just follows the mechanical response of your turbo to whatever duty cycle you're running — no oscillation, no hunting, just a smooth curve. Get that close first and PID has a small predictable job rather than fighting a bad baseline.

In practice I ran 100% duty cycle through about 4000 RPM then ramped down to 62% as boost came in, which got me to roughly 14 psi (my target was 15) at handoff then a small dip around 5500 before flattening out. I tweaked it to run 100% again at 6-7k to try to recover that but I think with running the single port controller on a 5psi spring, it just can't hold the gate closed.

I intentionally left the open loop table targeting around 14 psi — slightly under my 15 psi target — so PID always pushes in one direction rather than hunting both ways. I spent probably 45 minutes street tuning my 'setup' mode bias table. Then another 20 going through P first, then I. Ended up at P=30, I=25, D=0 and got a stable curve climbing to low 15s. There's still some fluctuation. When I switch from 100% to PID, I'm at about 14psi and slowly gain to just over 15 by 5500, then lose psi until redline (again i think this is just single port limit on 5 psi spring).

Using the hold wastegate closed until within 10kPa of target was a game changer. It handles the aggressive part of spool more reliably than P gain ever could, so P only needs to manage fine correction near target. Doesn't need to be high at all once that's set up.

At the top of the rev range boost drops off slightly despite 100% duty cycle. If duty is already maxed and boost is still falling, PID can't help — the wastegate is already fully closed and exhaust backpressure is physically winning against a 5 psi spring. Dual port controller would help but half a psi falling off at 6-7k isn't really worth chasing. Tehcnially i have a dual port, but at this point i'm happy and don't care to chase that half psi.

 

This is a great video explaining PID tuning, it explains what the PID values are, how to tune them quickly and shows their impact on output:

 

Nice. I used this site (https://www.luisllamas.es/en/pid-controller-simulator/) to help me mess with the PID values to get an understanding of what each did and how they effected output. I put that together with getting my open loop (really setup mode in MS3) as close as I could and I believe that made the PID tuning remarkably easy. My goal in the open loop was to get the tune just below (with .5 to 1.5psi) of where i wanted it. My boost isn't perfect, but it is really damn close. I have a goal of 15psi, and I ramp up to 14 before the waste gate is opened within 10kpa of target, and instead of spiking to 16psi within 200rpm, i climb to a little over 15psi over the next 1000rpm, then my boost control/wastegate spring run out of gusty and i slowly lose down to mid/low 14s until redline. This is semi-by choice, i dont want a larger spring so I don't have to swap it out for track days and losing .5psi just ain't worth it for me to continue chasing.