Heya!

So, the patient is - heavily modded RS6 C5.
Custom hybrid turbos, 550cc injectors, wagners, 6-speed, etc etc.
It's been fitted with EBC and N75 for now just hangs in the air. So, basically ECU is just running blind in terms of boost control.

The bin is 0002 (366304 IIRC) of the 4D1907558.

The problem I encounter is a random throttle cut after a few seconds WOT run. Attached is the log which shows 1-2-3-(TC) pull, then after some time it "recovers" and allows WOT again. The second TC occurs after ~5 secs in 4th gear full throttle. Excel file has those moments highlighted. CSV is for your convenience.

Now, before you start insulting me and saying that I should stay away from tuning cars - I didn't build, nor tune this car. 
I'm more than willing to "do it properly", to return to N75 control & get rid of the silly EBC, "polish" the tables and so on. There are also numerous other problems, such as the need for 5120 mod, bigger MAFs, probably bigger injectors or bigger FPR - that's still a long way from now.

I'm not exactly a complete noob at tuning, I spent around 2 months a couple of years ago creating a "proper" OLS file for this bin, trying to define as much tables & variables as I can. Also spent some time trying to reverse the bin in IDA, but didn't get as far there as I'd like.

Anyways, what are the possible causes for the TC?
Ruling out knock & temps since logs do not show anything bad there, leaving:
positive/negative boost deviations according to WIKI(which we will see A LOT of with standalone BC).
The second pull (single gear) rules out (or does it?) the underboost condition - there are whole 5 seconds where actual boost is pretty much at requested level.
For overboost, KFDLULS has been FF'd out.

EDIT: Details

Nopers. Well, apart from N249 disconnected and some random lean/rich codes related to part throttle fueling. Occasionally also MAFs max out (on cool weather mostly).
Nothing related to boost.

LDRXNZK is only ~10% lower than LDRXN in this bin, not 2x+ times.
rlmax_w  goes from 217+ to 99.75.
And it shouldn't knock anyways, - plenty of fuel, compression ratio has been lowered, angles are not too aggressive.
Not that easy!

Although I'm fairly sure that it's some safety feature intervening indeed.

Oh, EGTs are also not that bad, under 1K deg C.

EDIT:
Checked KFLDHBN - it allows 3.0 pressure ratios at and below 60 deg C IAT.
I guess I will log some more "internal" boost-related params.

Please post an unedited ME7L log so it can be parsed by ecuxplot

I agree that there are some severe ignition retards happening, but it's only after throttle has been cut already. Most likely due to part-throttle maps being sub-optimal. WOT it's still fairly safe, up to -6 worst case. And I also agree that it should be dealt with, but it's not the case for the TC itself.


Attached is the original unedited log.

EDIT: Did I understand correctly that B_furena means that any safety mechanism is activated?
EDIT2: Any idea what can trigger overboost if the KFDLULS is FF'ed out?

Thought so. This whole car is a mess.
But I gotta give credit to builders - they made it run, boost up to 1.87 bar and haul ass. Now I just gotta make it run properly.
I will start work on 5120 in near future, once I get to know this bin a bit better.

I guess I'll have to start with this, yep. Then implement the 5120 if I'm capable enough and turn it up to 27-28 psi peak. 
Anyways, I'll test the upped LDORXN tomorrow and post back the result.

If anything, I'm spending this time learning. So it's not all wasted. But I get your point.