A4 B6 2.5 TDI 180 hp BAU, power loss below approximately 2800 RPM

Hello to all the diesel mechanics community,

I bought the Audi a few months ago, and now I'm having the following problem:

When I start in first gear, it feels like I'm driving into a hole, and turning sometimes feels dangerous because I just can't seem to get the car moving properly. It feels like it has insufficient power from the first gear to the end of the rev range.
In second gear, the behavior is similar, but starting around 2800 RPM, you feel a noticeable surge of power, as if the torque kicks in about 1000 RPM later than usual.
In the third gear, the engine's maximum RPM is approximately 2500.
In fourth gear, in my opinion, it has a fairly normal characteristic. You can tell that it starts to pull from around 1300 RPM, which is what you'd expect from fourth gear. What I mean is, you don't feel any unusual lack of power here (it's already better in third gear, but still a bit weak for third).
I have already replaced the mass airflow sensor (the airflow mass readings were significantly lower before).
For testing purposes, I also removed the pressure sensor from the turbocharger and actuated the lever for the variable turbine geometry (VTG), which moves freely. The can is also sealed.
Since the timing belt was replaced before the purchase, I checked the timing and it's currently at 4.2 degrees retarded and 14.6 degrees advanced. I don't think it can be primarily due to the fact that his SpO2 level is at the lower end of the acceptable range?
I once logged data from measurement blocks 3, 8, and 11.
I think my feeling is being confirmed.
In the first gear, the soot reduction system is active for a relatively long time, which makes sense to me. I can't imagine the turbocharger being able to build up reasonable boost pressure within those 1-2 seconds.
I've attached the log.
I'm almost starting to accept this as normal, but not long ago I drove a 163 hp car that performed better and had a more typical driving feel.
Oh yeah, something just occurred to me.
The fuel temperature consistently remained between 30°C and 40°C, even after heating, which seems low for the LOG values. Shouldn't it be above 100°C? Could this also be the reason why the fuel quantity isn't being increased to compensate for the higher temperature? If that were the case, wouldn't it have to initially provide full power when it's in a cold state?

Sorry for the long text,

Best regards,
Tobi.

"In my BDH engine in my 2003 Passat 3BG 4-Motion, I experienced a similar issue. The cause was a vacuum leak in the system between the vacuum pump and the brake booster, due to leaky grommets and a torn hose leading to the engine mounts. Since I fixed it, the turbo kicks in around ~1500 RPM as it should."

Hello,

My BRE also had similar symptoms; the membrane of the intake manifold control valve was torn, which prevented the proper build-up of vacuum.

Okay, let's check the vacuum system for leaks.

Best regards, Rainer.

Oh man, there are so many possibilities... is there any way I can check the vacuum system? Are there any documents that show what a vacuum system looks like and how it works? I have no idea how it's set up.

MrMcFly79 wrote:

Oh man, there are so many possibilities... is there a way I can check the vacuum system? Are there any documents that show what the vacuum cycle looks like and how it works... I have no idea about it...

Suction should be applied to the hose leading away from the vacuum pump, and ideally also to each membrane, as these can also leak depending on their position.
And of course, check the vacuum hoses for damage caused by martens, and make sure that no hose nipple is cracked.

Best regards, Rainer.

Quote:

The hose that leads away from the vacuum pump

sucks .

"But shouldn't that also be visible in the log files if there's something wrong with the vacuum system?"

MrMcFly79 wrote:

but shouldn't that also be visible in the log files if something is wrong with the vacuum pressure?

Unfortunately, the vacuum pressure is not measured anywhere. You only see delayed reactions, for example, when requesting boost pressure if the turbocharger is controlled via vacuum.

Best regards, Rainer.

Okay. What aspects that could potentially affect performance are controlled by vacuum regulation?
I know "Druckdose," and that's where it stops.

It depends on your engine; in newer engines, many functions are controlled electronically.

At your place:
Okay, I'm ready. Please provide the German text you want me to translate.

Best regards, Rainer.

I have connected a simple hand pump that creates a vacuum, and I am reading the pressure gauge to see if the vacuum is being maintained or if it is dropping.

That's how I gradually figured out the performance issues with my BGD motor, and the BKV (brake valve) responds better now that everything is sealed properly. Before, I had a brake pedal that would get hard relatively quickly.

Okay, now I just need to know where the pump is located .

MrMcFly79 wrote:

Okay, doki, now I just need to know where the pump is located

.

Driver's side, at the rear of the cylinder head, driven by the timing belt.
The hose runs through the injection molding machine to the buffer cylinder (BKV), with a branch connection leading to the vacuum system.

The link from Rainer above explains the rest about the two circles (boost pressure control/AGR).

Regards, Mpire.

Great!
Thank you.

Okay, I've blown and sucked on the accessible hoses.

Image 1: Suction is possible with hose 1, but blowing is not.
Image 2: Hose 2 is reversed, and if I'm seeing correctly, it's identical to hose 1.
Hose 3 goes to the VTG, the hose at the pressure sensor is disconnected, allowing for both suction and blowing. Hose detached from the solenoid valve and suction applied, VTG retracts and remains in position.

Engine started:

The VTG (Variable Turbine Geometry) is engaged, and there is a vacuum at the hose, as is the case with the EGR (Exhaust Gas Recirculation) system.
If I disconnect hose 2, the VTG goes down. If I reconnect the hose, the VTG slowly increases.

What do you think about that?

Best regards,
Tobi.

Quote:

When I disconnect hose 2, the VTG goes down, and when I reconnect the hose, the VTG slowly engages.

How slow? Please perform a basic setting adjustment on the engine control unit, channel 11.
The engine must run at idle. In this process, the VTG is alternately turned on and off.

The VTG (Variable Transmission Gear) must return to its original position within half a second and should not be strained.

Best regards, Rainer.

The rubber grommet in the last photo, which passes through the partition to the water tank, has repeatedly caused vacuum problems in TDI engines.