Boost creep on limiter.


Fresh Recruit
Hello guys, not a gt turbo, actually not even a toyota but a fiat. I can't find anything regarding my issue on fiat forums, so I thought there's a chance you could help me since this is a common setup on your cars (td04 13t). I read the thread regarding boost creep but I'm having somewhat of a different experience, that's why I'm creating a new thread.

Firstly, let me tell you about my setup. The turbo is a TD04L (italian versions of the 13t but with a somewhat smaller hot side). These are diesel turbos similar to the 13t but have a smaller hot side which means better spool but smaller peak horsepower.
76mm (3 inches) downpipe and a 63,5 (2.5 inches) custom exhaust system.
76mm (3 inches) cold air intake
Stock exhaust manifold.

I'm running a Greddy boost controller with 3 boost pressures. OFF at 0.8, LOW at 1.4, HIGH at 1.7 bars.
The issue is that at OFF and LOW pressure (if I drop the BC duty below 1.4 bars at LOW pressure) the car will boost creep at limiter to 1.4 bars.
To be exact, I have an adjustable wastegate actuator, no matter what spring I install (0.6, 0.8, 1.0, 1.2 bars) the car will start boosting at the desired pressure but will ultimatly creep to exactly 1.4 at 7100 revs but what's strange is that my HIGH pressure (1.7) is working as should, hits 1.7 and then drops to about 1.55-1.6 which is normal.

I'm leaning towards a too free exhaust and intake but what's got me scratching my head is why it only creeps at pressures lower than 1.4 bars and works normally at anything above that.
Any help will be gladly appreciated!