Initial Details into How The Boost Based Tuning Works with AccessTUNER

[Christian.]

Here is some initial information about the boost-based tuning that I've been able to put together for ya'all. I will update this as time allows. Please let me know this can be made more clear or more easily understood.

Use Boost Based Dynamics (Boost Control)

When this box is checked, the ECU will function using several Boost Tables and the MAP sensor readings in order to control boost. This should provide what you are calling "PSI tuning" vs. the “Load Tuning” the factory implements. In other words, the ECU will take the result of the Boost Target table and compare it against the actual Boost measured by the MAP sensor. If Actual Boost is greater than target boost, it will reduce the WGDC (attempt to lower actual boost). The opposite is true if Actual Boost is less than Target; the ECU will then use the authority given to it within the Boost Dynamics table to increase WGDC.

The ECU will use the reported “Throttle Position” in the datalogs for looking up the Boost Target values. Since the ECU reports ~74 for WOT, the ECU appears to not be using the 4 final rows from 75-100. This loss in resolution should not hinder your ability to properly calibrate Boost Targets. Without including the last four rows, this ECU still has 15 x-axis RPM break points and 13 y-axis TPS break points for the psi-based Boost Targets table. This is more than sufficient considering that the GTR has a Boost Targets table that is 8x8 in resolution.

Depending on how your boost control system is mechanically set up, you may need to modify other tables within the Boost Tables folder in order to allow for appropriate boost control. We will go over this in greater detail below.

The following screen shots and logic descriptions explain how the closed-loop boost control system functions using this custom coding.


1st - The ECM logic will “look-up” what the Boost Targets have been calibrated to based on RPM and Throttle Position look-up values; achieving these Boost Targets is the ECM's primary goal for closed-loop boost control system.


2nd - The ECM logic will then “look-up” what the WG Duty Cycles have been calibrated to based on RPM and Throttle Position look-up values; the ECU will then drive the boost control solenoid in order to achieve the desired Boost Targets.

3rd - At very fast rates, the ECM take readings from the MAP sensor and measures the Delta Δ (or difference between) the desired Boost Targets and the actual measured Boost for the measured RPM and Throttle Position.


4th - The ECM logic will then “look-up” compensatory Boost Dynamics values that will modify the WGDC in order to achieve the Boost Targets for the corresponding RPM and Throttle Position.

The ECU logic will then cycle over again in this “closed-loop” operation.

The values in the Boost Dynamics table give the ECU the authority to modify the WGDC during over boost and under boost conditions. The values on the right hand side of this table give the ECU the authority to reduce WGDC during over boost conditions. The values on the left hand side of this table give the ECU the authority to increase the WGDC during under boost conditions. If you are getting significant boost oscillations, then you may need to fine tune the values in this table or you may need to recalibrate the WG Duty Cycles table. Generally speaking, it is easier to start with less WGDC than you need in order see how the turbo responds.

One easy way to help figure out proper WGDC values is to set the WG Duty Cycles tables to 25% and then run the car at WOT with the desired Boost Targets set. The ECU will then try to do everything it can within its authority (Boost Dynamics table settings) to figure out the proper WGDC values to run in order to hit the Boost Targets. Simply observe those values and begin to enter them into your WG Duty Cycles table until you see the ECU is controlling boost very consistently.

I've also attached a base calibration that you are welcome to start with.

2007-2008 MS3 = Stage1+SF 93 v107 FMIC BT vF.ptm
2009 MS3 = Stage1+SF 93 v107 FMIC BT vA.ptm
2006-2007 MS6 = Stage1+SF 93 v105 BT vA.ptm

XOXO,
Christian.