Allroad AKE V6 2.5 TDI - No power below 2500 RPM

Hello everyone,

I recently purchased an Allroad with an AKE (automatic clutch engagement) and a manual transmission. The engine has approximately 240,000 kilometers.

Now, the engine doesn't really start producing power until around 3000 RPM. Below that, it's completely dead – I mean, really dead. There are no error codes stored in the memory. No defects were found, except for a nozzle that can easily fall outside of the specified tolerance range during idle operation.

I have also read many posts in this forum and tried to eliminate as much as possible.

The following items were checked and/or corrected:

Compression test: 29 / 30 / 31 / 30 / 29 / 28 BAR.
- LMM (Mass Air Flow sensor) replaced (Magnetti Marelli).
- Vacuum system sealed.
- Timing belt replaced, valve timing adjusted, injection timing set.
- Diesel filter replaced, including the valve on top, and the system has been bled.
- AGR valve checked for smooth operation, vacuum actuator checked.
- AGR magnetic valve replaced.
- Checked the pressure side (charge air) for leaks.
- Replaced turbocharger solenoid valve.
- Replaced boost pressure sensor.
- Replaced the coolant temperature sensor (it was defective).
- Engine control unit checked (or tested against a suitable replacement part).
- Catalytic converter tested/inspected (including a test drive with the exhaust temporarily disconnected from the catalytic converter).
- The turbo was temporarily swapped with another used one (which the seller provided) for testing purposes.

The turbo currently installed is a refurbished one purchased online, and it was installed about 2 years ago. No idea how good it is...


The vehicle starts well, runs smoothly, doesn't jerk during acceleration, and the turbocharger doesn't whistle.

But, as I said, the performance comes very late, and probably not in its full extent.

I also took a look at the measurement values during test drives.
The fuel injection volumes are likely being achieved, and the air mass is also entering the correct range at higher engine speeds. The boost pressure is also achieved at 3000 RPM.

The question now is, what's the catch?

Does anyone have any ideas?

Regards,
Okay, please provide the German text you would like me to translate into English.

Hi,
Since you seem to have VCDS, and after the unsuccessful parts replacement attempts, my suggestion would be to continue working with diagnostics.
The compression seems to be fine. I cannot assess how well the valve timing is set unless you provide more details.
Please provide the vehicle make and model, along with the year of manufacture, and also a vehicle scan so we can get an overview.
I would start by recording the target/actual values of the boost pressure, the control signal to the N75 valve, and the torque limitation (all with full throttle from 1500 rpm to 4000 rpm). There might also be a specific test procedure for the boost pressure for the engine. You'll have to look that up in the RLF.
Without air, there's no fuel, and without fuel, there's no torque.
hg
Herbert.

"The V6 TDI engines are really sluggish at low RPMs... my AKN engine barely moves forward below 2000 RPM... and the Allroad is considerably heavier."

@Herbert:
Hello Herbert, please find the logging files attached. I hope I have captured the correct data. The sampling rate seems a bit slow, and I'm not sure if it's due to the vehicle/interface and if that's normal, or if it's related to my laptop. I've also attached the Autoscan. It's an Audi A6 Allroad, manufactured in 2001. AKE toggle switch.

If I have misunderstood something, I would appreciate feedback.

@Rüdi:
I understand that the V6 TDI is not a high-performance sprinter. The car is currently driving like an 80-year-old person with a walking stick.

Regards,
AL

Do you have a comparison?

Hello Ruedi,

I currently don't have a direct comparison against a "working" V6 TDI.

However, I drove an AFB (presumably referring to a specific type of vehicle) for about 6 years and 150,000 kilometers. Therefore, the 2.5 TDI engine is not entirely unfamiliar to me.

Regarding my current AKE:
He's not just tired; there's a serious problem.
It's difficult to drive on the highway in 4th or 5th gear because the car slows down with even the slightest incline. The turbo doesn't kick in noticeably until around 2,500 RPM. It drives like an old Mercedes S-class diesel with only 80 horsepower - and that's not an exaggeration.

Greetings.
AL

Hi,
In the last two files, it appears that the boost pressure is lagging behind.
Take a look at this.
Okay, I'm ready. Please provide the German text you want me to translate.
Okay, I'm ready. Please provide the German text you want me to translate.
Okay, I understand. Please provide the German text you want me to translate into English. I will only provide the translation.
hg
Herbert.

@Herbert:
Thank you for the helpful links. I've looked into the topic again and checked everything thoroughly.

The vacuum line seems to be in good condition. I also connected a vacuum gauge and used the tester to switch the EGR and VTG valves. The vacuum pressure immediately rises to the required level when the valves are switched and remains at that level. The VTG actuator also moves, as described in the links you provided. I would say everything should be fine.

I also had the opportunity to test a new Hitachi LMM. This made no difference. The LMM should be working correctly. However, I'm surprised when I look at the injection quantities. The injection quantity limitation seems to be coming from the mass airflow sensor. When I look at the data, the actual injection quantity matches the target injection quantity from the LMM. The desired injection quantity (based on the throttle position) is much higher. Or am I completely wrong about this?

What surprised me a bit:
I once disconnected the mass airflow sensor (MAF) and drove without it - I would subjectively say that it even runs a little better without the MAF (but that might be my imagination) - definitely not worse. And if I drive the car without the LMM (lambda sensor), the fuel injection amount is also marginally higher.

I also checked the normal correction values for the fuel injection quantity adjustment (idle speed control).
All cylinders are floating between 0 and -1, while cylinder 1 is an outlier with values between +2 and +2.6.
Can this lead to a significant drop in performance?


After prolonged operation, I've also noticed that approximately every minute, a noticeable air bubble passes through the transparent diesel line... I should probably bleed the system again. The vehicle starts well and runs smoothly.


I've also noticed in the AGR logs that the desired and actual AGR rates often differ significantly. I don't know how the control unit measures that.


I am grateful for any suggestions.

Regards,
Okay, please provide the German text you would like me to translate into English.

Hello.

It's possible that the VTG (variable turbine geometry) is not properly adjusted on the turbocharger. If the AGR (exhaust gas recirculation), MAF (mass airflow sensor), and vacuum system are all functioning correctly, this is something that should be checked. You can quickly see what the VTG's duty cycle is.

Since I didn't find any significant issues in the log I was reviewing, please mark the length of the VTG adjustment rod (precisely! Use a color mark on the adjustment nut, and measure the rod length) and shorten it by one (1) revolution. Then, test drive.

Best regards, Rainer.

@dieselschrauber:
Hello Rainer,

Thank you for your reply and the tip.

Here's a story about turbochargers:
When I bought the vehicle a few months ago (with the performance issue), the seller gave me an old turbocharger. This turbocharger was replaced about 3 years ago. The shaft on that old turbocharger had already been tampered with, as you can see from the damaged paint. Nevertheless, I installed it, but the performance remained unchanged. Neither better nor worse.

Today, I replaced the turbocharger again – this time with a rebuilt one from Magnos Turbosystems GmbH. I also replaced the EGR valve (MagnettiMarelli) at the same time. And now the surprise – it's running just as poorly, or even slightly worse, than before. In addition, when operating at full load in the 3rd or 4th gear for an extended period, the "regulation limit exceeded" error occasionally appears at 2000-3000 RPM.

I'm starting to feel a bit resigned.

Regards,
Okay, please provide the German text you would like me to translate into English.

Hi,
Always drive slowly. What kind of exhaust cleaning system does the car have? Oxi-Kat and EGR, or perhaps a DPF retrofit?
hg
Herbert.

@Herbert:
Yes, it has a retrofitted particulate filter installed by Remus. I also found this on the undercarriage.

I even got the documents from the previous owner.
This is a Remus PMS-RS6. According to... Protocol, manufactured in 2015.

If I'm interpreting the installation instructions correctly, the original catalytic converter was removed and the particulate filter was installed in its place.

Attached is a picture from the cultivation instructions.

Regards,
Okay, please provide the German text you would like me to translate into English.

Hi,
It's already clear that there's insufficient boost pressure (and therefore, not enough air being drawn in). Regarding the charging aspect, you've tried and checked various things, but without any success.
Now I'm wondering if the back pressure in the exhaust system might be too high, and a retrofitted, clogged DPF could be a possible cause. I'd like to put this idea out there for everyone to consider.
hg
Herbert.

Hi, that was initially my suspicion too... you read a lot about added catalysts. At first, I removed the pre-catalyst and blew it out and inspected it with a light. It seemed to be in good condition. I at least took a look at the retrofitted DPF with an endoscope camera (at that time, I wasn't even aware that it was a particulate filter, I thought it was just a cat from an aftermarket supplier), but it has a very coarse structure and looked quite free. However, I now believe that the part located further back in the housing does not have a finer structure.
I once also mounted the exhaust system to the turbocharger, placing about 10mm spacers in between, and drove with it like that. However, no change could be detected.

Can the back pressure be checked using simple methods?


Furthermore, the question arises whether adding a catalytic converter would significantly (or even much more) reduce the vehicle's performance, especially in the upper RPM range? As the exhaust flow increases, the back pressure would also increase. Or am I mistaken?

Regards,
Okay, please provide the German text you would like me to translate into English.

@Herbert:
@dieselschrauber:

I was also wondering if there might be something stuck in the intercooler? The sensor is located behind the intercooler. Is this a theoretical approach that should be explored?
Regards,
Okay, please provide the German text you would like me to translate into English.

Hello,

In my opinion, the air mass should decrease more at higher engine speeds when there is a blockage in the intake manifold.
I don't think it will be the LLK.
Perhaps the wrong vacuum sensor is installed on the charger, or the adjustment rod is incorrectly adjusted.

Best regards, Rainer.