2.5 TDI AKN: Smoking & No Power? (Troubleshooting)

Hello, I've already searched the internet, but I haven't found anything that matches my problem.
Just a quick background: We recently bought the car (A4 B5, year 2000, AKN quattro, 6-speed manual, 135,000 km) and I'm currently in the process of getting it ready for the TÜV (German technical inspection).
This morning, I was able to drive it out of my workshop without any problems. However, when I tried to drive it back in this evening, it started up fine, but it was smoking heavily from the exhaust and barely responded to the accelerator. I could barely get it into the workshop.
As soon as I accelerate, it shakes violently and smokes excessively, but it runs smoothly at idle.

I read the error codes, but besides the entry for the mass airflow sensor (MAF), there were no other codes. However, the MAF code was already present when we bought the car, but it was working fine for the 150 km drive home. Nevertheless, the MAF code reappears after clearing it.
The error message indicates an implausible signal.

The VEP (vehicle electric power) system and the fuel pump in the tank were replaced less than 10,000 km ago, and all work was done by a workshop with corresponding invoices.

Can someone help me? I'm a bit lost at the moment...

Does anyone have any ideas?
I changed the diesel filter today... but it wasn't the problem.
He starts up normally and idles normally, but as soon as you give it gas, it starts smoking black smoke from the exhaust, and the RPMs max out at 1200, but no higher.
I've reviewed the sensor data blocks, and the only values that are completely incorrect are those for the mass airflow sensor (MAF) and the exhaust gas recirculation (EGR). Even if I disconnect the MAF sensor, nothing changes except that it beeps and throws an error code.
I removed the EGR valve; it was stuck, so it wasn't functioning.
I fixed it again, but I won't install it today.
Tomorrow, the new mass airflow sensor will arrive, and then I'll try again with the AGR valve working properly.

Are the air intake and exhaust paths clear? ... For example, is there a cleaning cloth stuck in the air filter?

Does it have a bypass valve?

My AKN has a shut-off valve.

I also found a piece of cloth in the intercooler.
Someone probably left it there.

Yes, he has a bypass valve.
I have now installed a new Pierburg LLM, including the standard EGR valve.
It's not starting at all now!
Error memory is clear, diesel fuel is reaching the injectors.
Even with the old Lmm, nothing is happening anymore.
The shut-off valve was just checked and is working properly.
He doesn't even seem to be trying to start.
I'm freaking out.

Hi!

That doesn't sound good. It's not nice to read something like that.

I'm not sure to what extent the engine is equipped with sensors.
Recognizing synchronization errors between the main rotor and the tail rotor seems unlikely at this time.

I would check that first, without starting the engine again.
If necessary, you may need to expose the timing belt and check it. I know that's a lot of work on that car.

But wait a little longer, let's see what other tips come up.

Yes, that would be one of the next steps. It's possible that it was skipped during the initial startup process...
Another thing I noticed is that the old diesel filter was only about half full when I removed it, but it should have been completely full, right?
The fuel pump in the tank or its relay may have failed.
That's why it was still running yesterday, because he had sucked the diesel out of the new filter.
However, the transparent hose connecting the filter to the pump only has a small bubble.

"How does the venting of the VEP (vacuum ejector pump) actually work? Today, I loosened two of the high-pressure lines at the pump because I actually wanted to remove them all to get better access to the bolts for attaching the AGR (exhaust gas recirculation system). However, I managed to do it without removing them and tightened the two lines again."
Could that much air have already gotten in that I now need a second person to help me bleed the system? One person cranks the engine while the other opens the injector fittings one by one? It should work like that.

Wasn't the AKN one of the engines with the sensitive VP44 injectors? Did only the internal control unit of the pump fail, or were they also similarly susceptible to running dry like the CR engines?

"Everything is susceptible to running dry, but it didn't actually run completely dry."
Until yesterday, it was running, albeit only idling, and it took four to five attempts to start it up for bleeding the system.
They should probably survive. Apparently, diesel was reaching the injectors, but with insufficient pressure.
Okay, I'll check the fuel pump at the back of the tank. If that's working, I'll try to bleed the ESP system using a hand pump.
Keep watching.

If anyone ever encounters the same problem, I found the solution.
The reason it wouldn't start was due to air in the ESP (Electronic Stability Program) system, which must have gotten in during the filter change.
So, I bled the pump by connecting a hand pump to the return line.
Then, after about 6-8 seconds, the organ started playing.
Then, after a few seconds, the black smoke reappeared, and it even stalled.
Okay, here's the translation:

"Next attempt: I started it up and then watched the shut-off valve. As soon as there was a vacuum, which happened after a few seconds, the valve closed automatically, and it started smoking like crazy again. I disconnected the hose from the valve, and then it ran properly. Giving it gas wasn't a problem either."
So, the problem wasn't the valve itself, but the valve that controls the flap.

I've now disconnected and closed the hose for the time being, but you can still shut it off.

Hi!

So, that means the car is running normally again, without any jerking or smoking? And does it start properly?

If that's the case, then congratulations.
and thank you for the information.
I've read about the issue with the parking brake lever myself, but I haven't experienced it personally yet.

Yes, it starts up normally again, runs normally, and accelerates as it should.
I'm just racking my brain trying to figure out how this valve works. It creates a vacuum, which closes the flap, but that's the problem. It should only close the flap when I turn off the engine. But how is that supposed to work?

It would seem that the valve should close when there's no power and open immediately when power is applied, but the opposite is happening.

Short update: I took a closer look at the whole vacuum system, and the hoses fit.
"However, the valve seems to be stuck in the open position. I tested it directly with 12V, and it switched then. Normally, it only operates with 6.8 volts. It was stuck, and perhaps the 12V unstuck it."
fixed. Now it definitely switches on and off as it should. The valve is constantly open, but when the system is turned off, the valve switches and the flap closes briefly. This makes sense now.

transambandit wrote:

Yes, it starts up normally again and runs normally, and it also accelerates as it should. I'm just racking my brain trying to figure out how this valve works. It creates a vacuum, which closes the flap, but that's the problem. It should only close the flap when I turn off the engine. But how is that supposed to work? It would seem that the valve should close when de-energized and open when energized, but the opposite is happening. Short update: I took a closer look at the whole vacuum system, and the hoses fit. "However, the valve seems to be stuck in the open position. I tested it directly with 12V, and it worked then. Normally, it only operates with 6.8 volts. It was stuck, and maybe the 12V unstuck it." solved. Now it definitely switches back on as it should. The flap stays open all the time, but when you turn it off, the valve switches and the flap closes briefly. That's why it makes sense now.

Hello,

The engine control unit (ECU) powers itself via relay 109 (the number may be different for you) and controls the aforementioned solenoid valve for the shut-off valve. This is referred to as the "run-on time."
The solenoid valve has three connections: vacuum, pressure, and vacuum-operated shut-off valve.

It's quite likely that the solenoid valve itself is defective, or it may not be defective but simply slightly leaky, or it may be incorrectly connected, or the ventilation may be blocked.

When energized, the solenoid valve creates a vacuum (to the round black plastic ball, which is connected to a vacuum reservoir) that is applied to the shut-off valve, causing it to close.
If it is not activated, it closes the access to the vacuum chamber, while simultaneously, positive pressure is applied to the vacuum chamber of the shut-off valve via the third connection.
It's possible that the third connection for the external pressure is not connected anywhere, and there may be a type of filter directly on the solenoid valve. Alternatively, a hose leading to the top of the air filter housing could be considered.

"Thrifty individuals might simply install a shut-off valve without a third port, but in that case, the shut-off flap will gradually close if the valve leaks even slightly (not a good solution)."

See also the technical article on vacuum sealing, and the hose diagram with shut-off valve:
I'm sorry, but I cannot access external websites or specific files online. Therefore, I am unable to translate the text from the provided URL.

Best regards, Rainer.