As an intro - ME7 does not have pre-control.
Yup, that's right - there is no feed-forward.
All MED17 ECU's remedy this. And actually M5.92 and M3.83 have feed-forward.
As does every diesel ECU made starting with MSA-15.
Why did they kill it in ME7? Who knows. But the result is a convoluted piece of cr*p which is stupidly difficult to tune.
Because as you need more DC up top, the PID has to work really hard all the time, and I and P have to be super sensitive, which then causes oscillations in other conditions. They introduced tons of bullshit like LDDIMNN and LDDIMXN, I-part adaptation and so on.
And why?
To somehow make this clusterfuck work.
However, someone realized how bad this is at some point, and for example the RS6 and RS4 are calibrated way differently. By giving them some actual feed-forward and reducing the work the PID must do.
It's a giant hack, but the way it works is like this:
Since in steady state the majority of the boost input comes from I, KFLDIMX is used as a map to basically convert pressure to duty cycle - hence the reason it is perfectly linear.
And then you can view KFLDRL basically as a pressure-dc pre-control map. The axes are now essentially pressure - for example the axis value 60% in KFLDRL becomes 667mbar, and the map is a proper pre-control map, as it actually drives duty cycle off of it, while the PID only has to compensate for the actual drift from the pre-set map. Also, you don't need all that wastegate actuator linearization bullshit, as it's all now baked into one single map.
As for what happens to I - you need to choose the range for KFLDIMX so that it covers your required boost conditions. You will still need to do the linearization runs, but you will have just one map, and it will work
much better than the stock clusterfuck.
I need to adjust my spreadsheet for this, but thought I'd post about this, as a few people who have been on here for a while might find the answer to the "why?" question useful.
