First of all, I'm really sorry but I don't have logs. The issue is from an old friend that lives in the other coast of the country and he doesn't know how to log.

He sent me a couple of videos from vcds live measuring blocks and I'll try my to explain it the best I can. If you don't want to post without logs it's ok.

Let's begin:
Golf IV AUQ
He puts a 2.5" downpipe and a custom remap on it. It pulls really well until one day. Since that day it runs poorly... However, the issue is @WOT, it don't hesitates, it simply doesn't pull. Driving relaxed on the motorway or in the city it runs ok.

FROM THE VIDEOS OF MEASURING BLOCKS AT WOT from 2500 to 6500rpm

Lambdas:
Requested around: 0.83
Actual: A couple of tenths richer

Boost:
Requested: 2400mbar at 3000rpm and goes down to 2000mbar at the end
Actual: 0.9-0.85bar manometric (External, maybe it was the map, but no) and 1900-1850mbar (from vcds). Constant.

MAF:
Very low, It doesn't corresponds to boost at all. Goes slowly up until 4000rpm to 100g/s and then it rises a very little bit to the end.

Timing retardation: The most important and notable issue
Always delaying like 4.5-6º in all cylinders, but when it passes 4000rpm rises very much, as much as 12º!!!


IAT: Low, as it doesn't eats air... below 40ºC

Injection times:
Low as well, a maximum of 17ms

N75 DC:
95.3%... so totally closed


He revised many many things. Tried with 2 mafs, new spark plugs, the coils are new from the VW campaing, 2 turbos (both the stock model), looked for boost leaks (but there aren't, just for trying, cause there wasn't any DTC) plugging and unplugging n75, n249, n112, DV, unplugging the wastegate actuator, measured both rail and pump fuel pressure which are ok, being richer than requested wouldn't make any sense for a bad pump. There are not DTCs, only those from the disconnected valves when disconnected.

We're running out of ideas. A colapsing inlet pipe? (which is stock)... but those timing retardations don't make sense...

I'd really apreciate your help. And again, sorry for not having proper logs mates.

But if my friend doesn't know how to log what do you suggest? sould I travel 1000km to log it myself?

And why did you move the thread to noob questions if the thing is to DIAGNOSE the problem?

I know I'm not above the rules, that's why I said sorry and that it was ok if nobody writes.


On the other hand, I'm not pretending to bet 500000€ to the correct answer. The purpose is to get ideas of possibly failing parts to check if they are ok.

Yeah, sure he knows how to make exactly a wifi access point through his smartphone...

While I try to explain him how to log, it will take a several days, it would really help if you guive your oppinion. It doesn't matter if you are not correct, as I said, it's only to check parts.

Flash original file back on, see what happens.

IamwhoIam:
I understand it's not the best way. But maybe and only maybe it was a quite common problem and logs were nor very neccesary this time. As I see, it's not the case.

adam-:
He told me now its remapped with the stock file, I forgot to put it in the OP, sorry. Anyway the problem persists.

ddillenger:
I could understand that if MAF were reading well bellow reality, but the thing is that reality is low. And he tried 2 mafs...


Thank you all and let's see if I can get some logs from him.

Maybe you guys were right... I managed to get some photos from the laptop of my friend via Whatsapp, It's the maximum I can get:

MAF plugged





MAF unplugged





Ps: I was wrong, that's not the stock file, that's a previous one, a soft st1 that went OK for a long time and when he put the DP he put a more aggressive one.

He says that, now with the MAF unplugged it goes better and the performance is near stock

Yes, if MAF were reading below reality, the result would be leaner than specified, not richer.

But as I said, he made several boost leak tests by introducing compressed air to de inlet pipe and pumping around 20psi it holds pressure until 15 seconds, which I consider normal and he doesn't hear any leaks... Plus there's no any DTC saying anything about pressure drops

I don't understand what you mean with "bvp", but as I said in te OP, he tried both 2 turbos and the blades are ok, the turbine axis rotates freerly and there's no roominess. One of them is totally ok and the other has the typical crack in the wastegate area... But is very tiny, anyway, same results with both.