Motor loses power at a certain RPM

For some time now, I've been having a problem where the ATD PD 74 KW engine is no longer delivering its full power. Engine mileage: 30 TKM.
I feel like he wants to, but he's not allowed to.
Pressure checked, with indicator.
The boost pressure increases up to a certain RPM, then decreases even though more gas is being applied. The vehicle continues to accelerate, but without any power.
The small "lever" on the turbocharger has already been thoroughly checked, (pump), and is in good condition.
No helpful information in the error memory.
Simple question: "What could it be"?
The answer might not be so simple, but I appreciate every attempt at help.
Hello from Lgk

The answer might not be so simple, but I appreciate every attempt to help.



How long has your fuel filter been in for??

I also experienced occasional performance issues (not always).
After changing the filter, everything was working perfectly again.

The diesel filter has been in for approximately 1000 km, and is the original VAG filter.
Greetings from Hoin, from Lgk

Hoin wrote:

Pressure check completed, with indicator. The boost pressure increases up to a certain RPM, then decreases even though more gas is given.

Hi,

give some specific RPM and pressure values...that the boost pressure is somewhere above 4000 rpm is normal.

However, if (for example) at 3500 RPM, 0.3 bar should be lower than at 2000 RPM (without overshoot), then there is definitely something wrong with the charging system.

The boost pressure increases when the turbocharger engages, reaching approximately 1.2 bar (this is when the car actually starts to accelerate), and then immediately drops back down to around 0.3 bar to 1 bar, even though more gas is still being applied. As already written, the engine is somehow being regulated.
It feels like someone suddenly grabs you from behind.
Greetings from Hoin, from Lgk

Hoin wrote:

The boost pressure increases when the turbocharger engages, reaching approximately 1.2 bar (at which point the car starts to accelerate properly), and then immediately drops back down to around 0.3 bar to 1 bar, even though more gas is still being applied. As already written, the engine is somehow being controlled.

Hi,

1.2 bar is a common value for the boost pressure during the induction of the air charge.
That the LDA shows "only" around 0.9 bar afterwards is, for me, not a real pressure deficiency (how exactly does the LDA show this??).

Your "adjustment" sounds more like a sagging LPFP (a common cause of performance issues in TDI) given the boost pressure.

Hi,

"Also, my AXR is doing the same. The boost pressure rises to a peak (1.1 bar) and then drops to just below 1 bar. The AXR feels a bit sluggish from around 3500 rpm, as it doesn't provide as much power as, for example, the 96kw engine." The 74kw motor is a glider and not a performance sports car.

... Oh, and one more thing: both engines have been electronically "neutered" in order not to put too much strain on the 5-speed gearbox.

Hi Ulf,
A new LMM from VAG was installed as a test, but there was no change.
The LDA is a VDO indicator and measures up to 3 bar.
Based on what I'm sensing while driving, I think the display is okay.
To Bertil,
You are right, there is a slight dip in power at the upper RPM range, but, as already mentioned, the dip starts at 2000 RPM.
I would like to discuss this matter of castration with you later.
Greetings, as above

Hoin wrote:

...in the upper RPM range, there is a slight dip, but as already mentioned, the dip occurs even at 2000 RPM.

That's way too early.

Quote:

I'd like to discuss that with you later.

Just take a look at the torque diagram (lower blue curve):

It's great to see the plateau... you can only achieve that with an intervention in the electronics.

By the way, the Passat with 74 kW has 250 Nm (unfortunately, TUNEline has depicted the ATD diagram there – 240 Nm)