E39a ECU boost limiting?

Trying to figure out what creates the desired boost to fall off, i have most limiters set to not limit. I get Full throttle, very little KR. MAF and VVE tuned and VTT tuned in areas to keep max Tq above Engine torque. Peak torque above Max Tq. I know the Max boost limit will set the high end of the Desired Boost but for some reason i can not get max Desired boost in the lower gears, each gear the Desired boost continues to go up 1-2 psi. I have raised DD and even lowered DD tables to keep predicted Engine Command torque below Max Torque but that does not seem to increased Desired boost down in lower gears. I have raised pressure max ratio, bumped up Airflow correlation on diagnostics, raised knock air mass. I tried to search for what could be limiting boost down low. If i do a 3rd gear roll on to load the motor harder the Desired boost is higher. I can get about 21-22 psi in first gear and 22-23 in second and 24 in third. Trying to get 24 + in first to hold steady boost throughout a full pass. What drives the desired boost PID?

Little update since i couldn't stop until i figured this out. I ended up bumping up the peak torque, brake torque limit and over boost limit up more and straight out. I originally had it following the torque curve closely and this was causing the boost curve to go down as peak torque went down i believe. I then still had a slight dip in desired boost during mid gear. The max torque values were not above predicted torque so i bumped them up, however bumping up the map VTT created a larger dip. I put the MAP VTT back to stock and only increased the Airmass VTT at the cam values under full throttle in the spark zone and this held desired boost strong. Increasing the Airmass VTT enough up then also allowed me to foot brake the car and launch without any limiting.

Thank you for the update.

Very appreciated.

So, generally the way to do it is to remember that if you want the boost to stay peaked where you set it, with the throttle completely open, driver demand must always exceed the max torque. So, set your torque tables where you want them to actually max out at (and then maybe lower it just a tiny bit to be safe. Be reasonable. Motors are expensive. lol), then set your driver demand tables from like, 80% to 100% pedal position, to go above what your max torque is set at for that area. If you are commanding more than the max at that RPM, pedal position whatever, it will, well, keep it at max. Short of any knock issues or static retard, burst knock, etc etc etc, you should be able to set your peak boost pressure and torque for a given scenario, and as long as you are commanding over that, it's still limited to where you set it, hence it will try to keep it at that limit.

Again, don't go nuts. Lol. Some cats are like "oh just put it to 500 across the board and zero this and that out, etc". Sometimes, just for like, tuning VVE and not chasing your tail, yes, you will set certain things out of range to either disable them or normalize them so you get good data, but you for sure want to keep some of these curves and gradients you see for safety and drivability. Also, don't even try to start making power WOT without a wideband and piped into your system. If you already have a wideband with a serial out wire, it takes like, 10 bucks to make a serial to USB adapter. I did a writeup on it on cruzetalk. :)

I have the MPVI1 pro that i have my LC2 wired to for logging. I have been working on tuning this car for a long time learning the ECU. I just recently found the limit of a stock framed turbo at the track yesterday, 26 psi is about at it will give in the upper rpm. I do still get some knock in the log on tip in or after launching then fades away to nothing. I still need to work on cleaning that up but i keep an eye on the plugs and don't see any detonation.

I have also found a new issue i ran into yesterday. I have been upping the VTT airmass slowly to get the car to launch hard without pulling back throttle. Well my logged max torque value falls off to zero after each gear change. I reduced boost to make less power and the max tq value was back to normal. Car still ran fine and wasn't pulling power but was odd.

@ATrim, thanks for sharing your experience. What vehicle is this?