[StrokeD]

Have you replaced the actual fuel regulator in the fuel rail? Based on the schematic someone else provided it looks like it’s just to the left of #5.

 

[StrokeD]

The pressure regulator for the low pressure side is built in to the fuel filter, as I understand it. Is there another low pressure regulator at the engine? Or are you talking about one on the high pressure side? I haven't messed with anything over there since the pressures on the fuel rail seem to make sense and track the command from the ECU.

Well, full disclosure: I am not the most familiar with the TFSI. I think I interpreted your original post as seeing low pressure at the tail, but I may have misinterpreted.
I was more brainstorming on whether it could be a failing pressure regulator (at the rail) but maybe I’m talking out of my behind? It would seem there is a vacuum operated regulator in the fuel rail itself, which IIRC should maintain around 4bar at idle (as mentioned by someone else).

But I don’t know for sure. I don’t know anything for sure. I’m brainstorming in the hopes it may spark a thought from someone else more than anything. 🤷🏻‍♂️

 

[StrokeD]

There could be a regulator there - and I definitely welcome the brainstorming! There's surprisingly little general knowledge about the 2.5L TFSI engine out there in the TT community, and the diagrams on the Audi parts website, the repair manuals, and LLLparts are not especially useful. This diagram from the self study guide for the engine doesn't show a regulator, but that doesn't mean there isn't one:

View attachment 539972

Since I actually heard the pump straining this time, it's now my #1 suspect. I know that noise because I installed the wrong fuel filter in my TT 3.2 several years ago and forced the fuel pump to work hard. If the pump doesn't fix the problem, I'll be looking for another low pressure regulator next.

Well, to me it looks like rather than a vacuum operated regulator, like I’m familiar with on the 1.8T, based on your self study image the HPFP and Regulator (Metering Valve) is one piece, which kinda shoots my theory in the foot. 😂

Unless the HPFP and N290 are separate components to make one (if that makes sense)? The Metering Valve should be what regulates how much pressure is delivered to the rail and if it fails it could either reduce necessary pressure or increase pressure. Ultimately though, if you heard the HPFP struggle, it would seem replacing that also replaces the metering valve.?

 

[StrokeD]

There could be a regulator there - and I definitely welcome the brainstorming! There's surprisingly little general knowledge about the 2.5L TFSI engine out there in the TT community, and the diagrams on the Audi parts website, the repair manuals, and LLLparts are not especially useful. This diagram from the self study guide for the engine doesn't show a regulator, but that doesn't mean there isn't one:

View attachment 539972

Since I actually heard the pump straining this time, it's now my #1 suspect. I know that noise because I installed the wrong fuel filter in my TT 3.2 several years ago and forced the fuel pump to work hard. If the pump doesn't fix the problem, I'll be looking for another low pressure regulator next.

But, after rereading some of your posts it sounds like your rail pressure both at idle and with load are performing fine.