A4 Engine Performance Issues AKN

Hello TDI experts!

I hope to gain some insights and suggestions from your collective knowledge to help me troubleshoot issues with my Audi A4, manufactured in 05/1999, with a 2.5 TDI AKN engine and 203,000 km mileage.
While I'm a very interested and eager car enthusiast, I'm definitely not a mechanic. The troubleshooting and repairs will be done by a friend who runs his own workshop. That's my understanding, at least.

Now, regarding the error:
The vehicle reaches a maximum top speed of 200-210 km/h. Previously, 220 km/h was no problem. The mass airflow sensor (MAF) was replaced 8 weeks ago as a precaution, but there has been no improvement. The solenoid valve located in the upper left corner of the engine compartment has also been replaced.
"Additionally, when accelerating while using the entire rev range, the power noticeably drops off around 2200 RPM and then slowly builds back up. I feel like there's a general lack of power. Of course, this is purely subjective!"

"The error message 'Intake manifold pressure regulation limit exceeded' occasionally appeared. However, this error has not occurred in the last 6 weeks."

Mein Bekannter meint, dass zur genauen Fehleranalyse eine Messfahrt unerlässlich sei. Said and done.

So, I used VAG-COM to log groups 03, 08, and 11 while performing full-throttle acceleration from 1500 to 4000 RPM in 4th gear. I repeated this process a total of 4 times.

I have processed the data into a chart for better visualization. The document is 12 pages long, in PDF format, and is 4MB in size.

Page 1-3, Measurement Series 1.
Page 4-6, Measurement Series 2.
Page 7-9, Measurement Series 3.
Page 10-12, Measurement series 4.

Here is the link: http://www.schuero.de/Diagramm.pdf

And here is the link to the data table: http://www.schuero.de/Tabelle.pdf

In some cases, 5-digit values (!) were recorded for the IQ scores. These original values are shown in the table, but in the chart, they have been converted to "1" because the chart would have been unreadable otherwise.

Perhaps you might find some time and inclination to look at the diagrams. I would, of course, be grateful for a layman's diagnosis or assessment. If you need to go into more detail, that's not a problem, as I will also show this thread to my acquaintance, who is a master in the field.

Thank you in advance, and best regards, Thorsten.

There's just a slight overshoot, but it doesn't affect the maximum speed.
Possible causes: Nozzle holes clogged, catalytic converter worn out, camshaft lobes worn, hydraulic lifters soft/worn.

There's a section in the diagram where the soot limit is briefly activated, and in that area, the turbo pressure is lower, and consequently, so is the mass airflow. This is likely causing the drop in power, but it shouldn't affect the maximum speed, which should still be achievable.

Okay, in addition to the points Christian mentioned, I'll take a look at the turbocharger boost control. If everything seems correct there, you can try driving without the catalytic converter for a short time. However, if the exhaust manifold has become clogged, you can skip that step.

Thank you for the answers so far.

A very important piece of information that I had forgotten:
This noticeable drop in power at approximately 2200 RPM is, of course, very noticeable while driving.
This issue was already present when I bought it in 2002, although it was much less pronounced. I remember it well because it was the only thing that caught my attention when I was buying it.

Therefore, I suspect that the "stalling" issue and the "V-Max" problem might be two separate issues that are not related to each other. Do you see it that way as well?

Would a log recorded while driving in 6th gear at full throttle on the highway potentially help with the top speed issue? If so, which parameters should I log?

To Christians: Are you referring to possible causes related to the "hanging" issue or the "V-Max" problem?

Dear Ms. Antje: I disabled the AGR valve by disconnecting the vacuum hose. There was no change in the acceleration behavior. The pressure drop remains. The boost pressure still rises to slightly above 2.5 bar, then immediately drops to 1.6-1.7 bar, and then slowly builds back up to the target value of 2.1 bar.
The first three data sets in my graph don't clearly show that the boost pressure reaches almost 2.5 bar, but it's more evident in the fourth data set.

What further steps would you suggest for addressing these two problems? Or do you need more information?

Sure, here is the translation of the text from German to English:

"The current status is:"
LMM is new.
The turbocharger wastegate solenoid valve is new.
All hoses checked for kinks and leaks.
Error memory is empty.
AGR valve deactivated by disconnecting the vacuum hose.
The VTG rod is in good condition.
"Test run in 4th gear, full throttle, using blocks 3/8/11. See the link in the first post."
Christian's comments will be forwarded to my supervisor for review, if possible without causing significant extra work.

Thank you for your efforts! Best regards, Thorsten.

The performance dip at 2200 rpm is not the cause of the missing top speed, but it may have the same underlying cause.

Since you've probably looked at the turbocharger pressure control system, you should look for something that affects the turbocharger pressure. I started by checking the valve timing and the catalytic converter. Did you have any air bubbles before your VP44 fuel injection pump?

Okay, so if you have the injectors replaced, the valve cover needs to be removed. That way, you can also have the hydraulic lifters and valve stem seals checked. If everything looks good, have them remove the catalytic converter and take it for a test drive.

Those are some very clear indications, Mr. Antje!
Everything will be noted and presented to my supervisor. I will report back later!

However, it might take a few days, as we first need to schedule an appointment at the workshop.

Best regards, Thorsten.

"Today I'm having the same problem. I've replaced everything, but it's not working. Audi doesn't seem to know what's wrong either. Please let me know if you find a solution."

What is everything?

Okay, so, first of all, the vehicle is an Audi A6 2.5 TDI with engine code AKN, manufactured in 1999.
- Boost pressure regulator
- Turbocharger
-LMM
- Vacuum hoses
- Diesel and air filters.
Audi has checked the fuel injection timing and base setting using the engine control unit. The timing belt has also been inspected and is in good condition.
The camshafts also appear to be in good condition.

MFG

You're having an LD problem, right? Then you've probably read about the catalytic converter issue (mentioned above), which you're still missing. Is the charge air cooler circuit blocked?

I think it might be related to the fuel; he's not getting enough, even when he's using full throttle, there's no power.
He gets tired when going uphill and having to pull, either the EPS (Electric Power Steering) is worn out or the motor control is no longer allowing it, but I don't know how to check that.
Best regards,

The pump cannot be tested in this way, but you could perform a data logging session using VAG-COM or the VW tester, focusing on measuring blocks 3, 8, and 11. Do this while giving it full throttle, preferably on an uphill section of a highway.

Okay, I'll do the test run and see what's happening. I'm wondering if the pump isn't supplying enough fuel, or what these readings should be.

Best regards,

If you read the technical articles, you would know. Try searching for "Systematic troubleshooting with VAG-COM" or "reference data."
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.
http://www.dieselschrauber.de/Solldaten_Main.html

Please first review the LD (Load Data), air mass, and quantity limits. Upload your logs here.

Just a reminder, here's an excerpt, and I personally recorded it while in the 4th gear from the LL (likely referring to a specific location or setting).

Quote:

Is everything okay so far? When driving at full throttle in 3rd or 4th gear, over a speed range of at least 2500 to 4000 rpm, the following measurement data blocks (MWB) should be logged and analyzed.

These data should be processed, ideally into a graph.