What the base duty table does
This table only exists when Boost Control Mode is set to Closed Loop. Closed loop lets you run more than one boost target, perhaps a low setting, a high setting and a target that rises with rpm. Each of those targets needs a different solenoid duty to reach it. The base duty table gives the ECU a starting duty for every target, so it arrives close before the PID corrections take over.
That's why the table's horizontal axis is Boost Control Target Pressure. Whatever target is active, the ECU reads straight down that column to find its starting duty.
Tuning it one column at a time
The key idea: only the column for the currently active target matters. Every other column is ignored until you switch to a target that uses it. Here's an illustration with made-up numbers, not a starting map:
- You run a 12 psi setting. The ECU pulls duty from the 12 psi column only. If boost settles above or below 12 psi (as read by the controlled parameter you chose in Boost Control), adjust that column until it lands on 12.
- You switch to an 18 psi setting. Now only the 18 psi column is used, so tune that column separately.
- Your target table climbs from 18 psi to 21 psi at a certain rpm. Below that rpm, tune the 18 psi column. Above it, tune the 21 psi column. Make each change only in the rpm range where that target is actually live.
We usually get each column close in open loop first, then copy those duties across. With a good base table, the proportional and integral gains only have to trim small errors, which keeps boost smooth.
Don't change the horizontal axis to Manifold Pressure. The ECU then has no way to look up a starting duty for the target it's chasing. And don't fill the whole table with one value. That will only suit one target, and every other target will miss.
Checking your work
Log boost, target and final duty together. If closed loop is making large, steady corrections at a given target, the base column for that target is off. Move the base value toward the duty the controller keeps settling on, and the corrections should shrink. Once the table is right, boost long term trim can handle small day-to-day differences, and the target pressure table is where you set what each setting asks for.
