Boost Pressure vs. Throttle: Odd Behavior

Hello,
First of all, thank you for the help regarding the ESP setting. It worked perfectly, and the TDI graph makes it really easy. Unfortunately, nothing has changed regarding the lack of power... and I've searched the forum, but I'm now a bit more knowledgeable, although my knowledge isn't enough to pinpoint the problem.
I logged data from measurement block 11 because I suspect a turbo problem. As expected, the actual value doesn't reach the target value (yes, I'm still looking for the cause), and it's consistently about 500 mbar too low. But what does the duty cycle mean? It's constantly at 5.1 (the gray line). Is something else completely wrong?
I have an A6 2.5 TDI (C4) with an AEL engine, which has a wastegate turbocharger, so a jammed linkage is unlikely. I've visually inspected the often-mentioned solenoid valve, and all the cable connections look good. The pressure lines also don't appear to be damaged. The only modification to the engine is a deactivated EGR (VA plate).
Can an expert offer some advice?
Thank you & best regards,
Burki.

I once had an AEL (Abgasendrohr links - left exhaust manifold) issue on a Volvo, where the rubber hose connecting the intake manifold to the wastegate actuator and some kind of plastic box inside (oil separator?) was deteriorated.
I installed a new hose without the plastic casing, and it worked perfectly.

-> Check the tire pressure and see what the TV does.

Best regards, Rainer.

Burki wrote:

As expected, the actual value does not reach the target value (yes, I'm still looking for the cause), and is practically constantly about 500 mbar too low. But what does the duty cycle mean? It's constantly at 5.1 (the gray line). Is something else completely wrong? I have an A6 2.5 TDI (C4) with an AEL engine, which has a wastegate turbocharger, so a jammed linkage is unlikely.

Hi,

"No warranty, starting from room 1Z."
The regulation only becomes active when the LD reaches its target and "wants to increase even further."
As long as the boost pressure is as low as it is in your case, the control system will initially remain inactive, waiting for the boost pressure to increase (which means the wastegate is closed) until it needs to become active.
It is normal for the TV to be constantly operating at its maximum power.

Hello,
Then you could test whether the system reacts when you artificially apply pressure to the hose (in my case, one hose runs from the intake manifold, which it should be).
But what can be inferred from the consistently low boost pressure? Is the turbocharger defective? It's also too low even when the turbocharger isn't active (below 2000 RPM). Could the intake side be blocked?
Best regards, Burki.

Burki wrote:

Then, you could test whether the regulation reacts when you artificially apply pressure to the hose (in my case, one hose comes from the intake manifold, and that's probably the one).

If the hose leads to the LD sensor -> yes.

Hi,
'You're right, the regulation only becomes active when the LD reaches the target value and 'wants to increase even further' (I found a Screenshot in a thread by dakoal, who also has an AEL, showing block 011).'
@Rainer: (This might be the wrong section, as it's not a problem related to a diagnostic tool for tax equipment.) I probably found the charge air cooler, but I'm not entirely sure: It's a small, black box directly connected to the bottom of the charge air cooler, with a hose connected to the side from the solenoid valve, and also two finger-thick hoses connected from the top of the cylinder head cover. It doesn't look like it can be opened without causing damage.
Questions: Can this can be opened, and what does the inside look like? What are the tubes connected to the ZK lid for?

Okay, while working on the hoses, I noticed that the hose at the turbocharger outlet is quite oily. According to forum reports, this indicates leaks or clogged intake passages (although the hose from the intercooler to the intake manifold is clean - I replaced it last year because of a hole ). You can't reach it from above. So, I'll have to take a closer look at the underside of the car soon.

Best regards, Burki.

Hi, so, the can I found that was faulty wasn't the pressure regulator can, and it wasn't its fault either... a typical beginner's mistake...
...but after some tinkering and searching in the forum, I now have the solution, and just to bring this thread to a proper conclusion, here's a summary (which is compiled from various answers from the forum; I've only put it together and adapted it to the AEL engine - and also verified it):

Wastegate control (AEL):
Solenoid ratio / Solenoid valve:

The AEL wastegate turbocharger operates with an overpressure control system. The duty cycle indicates the rectangular signal used to control the boost pressure control valve, which regulates the overpressure for the wastegate. The duty cycle provides information about the on and off times of the voltage, indicating whether the solenoid valve is open or closed.

Theory:
A 100% duty cycle means that the valve is completely de-energized. When de-energized, the solenoid valve allows the full boost pressure to act on the wastegate actuator, causing it to open at approximately 0.6 bar and limit the boost pressure.
The reason the regulation limits boost pressure when power is lost (rather than the other way around) is that, without power, the boost pressure should not exceed the wastegate pressure (e.g., in the event of a magnetic valve or pressure sensor failure).

0% duty cycle --> constant board voltage, the solenoid valve closes towards the wastegate chamber, resulting in unlimited boost pressure.

As the duty cycle decreases (i.e., the voltage increases), the valve reduces the pressure for the wastegate, causing it to open later and thereby achieving a higher boost pressure.

Okay, so it's practically useful for AEL:
Duty cycle 5.1: Solenoid valve open, no boost pressure to the control unit, full boost pressure goes to the intake manifold.

Duty cycle: 94.9%. Solenoid valve closed. Boost pressure reaches the control unit. Boost pressure for the intake manifold is limited.

With a boost pressure of only 0.6 bar, while approximately 1 bar is 'desired' (target value), the duty cycle, according to VAGCOM, is 5.1, and the voltage at the solenoid valve, measured with an analog multimeter, is in the range of 11-13 volts.


Causes of problems (lack of boost pressure):
It could be a solenoid valve, but it doesn't necessarily have to be. Also, clogged or defective pressure hoses.
(Pressure hose from the hydraulic pump to the main valve, or control hose from the main valve to the loader).
Air intake passages sealed (air filter clogged, hoses leaking, etc.).
Exhaust system blocked (e.g., clogged catalytic converter).
Loader / Pressure canister on the loader is defective.

In my case, it was the catalytic converter. If nothing can come out the back, then nothing can go in either, and pressure can't build up. I cleaned it out, and now it runs like new again.
Best regards, Burki.
And not to forget: Thank you to all the forum authors who have contributed something to the topic at some point; without you, I would still be searching!