What it does
In closed loop boost control, the ECU compares actual boost to target and corrects the solenoid duty. Derivative gain looks at how quickly boost is closing in on the target and pushes back against the correction as it approaches, to stop boost from sailing past. In other words, it's aimed at overshoot.
Our advice
For general boost control, leave it at zero or use a very small value. A conventional solenoid and wastegate setup responds slowly enough that proportional and integral gain do the real work. Too much derivative can make the controller twitchy or stop boost from ever quite reaching target.
If boost overshoots, look first at the closed loop base duty table. A base duty set too high is a frequent culprit. Only add a little derivative once that's right, and confirm the change in your logs.
For the full picture, see boost control setup.
