Allroad AKE V6 2.5TDI: Low Power Below 2500 RPM

Hello everyone,

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

Okay, here's the translation:

"The engine doesn't really start producing power until around 3000 RPM. Below that, it's completely sluggish – really, really slow. There are no error codes stored in the memory. No defects can be identified, except for one injector that slightly falls outside of the tolerance range during idle."

I've also read a lot of posts in this forum and tried to eliminate as many possibilities as possible.

The following items were checked and/or corrected:

Compression test: 29 / 30 / 31 / 30 / 29 / 28 BAR.
- LMM replaced (Magnetti Marelli).
- Vacuum system sealed.
- Timing belt replaced, timing adjusted, injection timing set.
- Diesel filter replaced, including the valve on top, and the system was 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).
- Turbo was temporarily exchanged with another used one (which the seller provided).

The turbo currently installed is a refurbished one purchased online, and it was installed about 2 years ago. I have 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 looked 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 RPMs. The boost pressure is also being reached at 3000 RPM.

The question is, what's the catch?

Does anyone have any ideas?

Regards,
Al.

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 is probably okay. I can't 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 for the N75 valve, and the torque limitation (all with full throttle from 1500 min-1 to 4000 min-1). There might also be a specific test procedure for the boost pressure for the engine. You'll need to check the RLF (likely referring to a technical manual or documentation) to find that.
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:
Hallo Herbert, anbei die Logging Files. Ich hoffe, ich habe die Richtigen Messwerte erfasst. Die Abtastrate ist etwas lahm, ich bin mir nicht sicher, ob es am Fahrzeug/Schnittstelle liegt und normal ist, oder ob es an meinem Notebook liegt. Anbei auch der Autoscan. Es ist ein Allroad A6 BJ 2001. AKE toggle switch.

If I have misunderstood something, I would appreciate feedback.

@Rüdi:
I am aware that the V6 TDI is not a high-performance sprinter. However, it currently drives 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 a vehicle with an AFB (Automatic Battery Function) for about 6 years and 150,000 km. So, 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.
Driving on the highway in 4th or 5th gear is barely possible, as the car slows down with even the slightest incline. The turbo doesn't kick in noticeably until around 2,500 RPM. Below that, it feels like an old Mercedes 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.
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.
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.
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.
hg
Herbert.

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

The vacuum line seems to be in order. I also connected a vacuum gauge and used the tester to activate 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 try plugging in a new Hitachi LMM (Mass Air Flow sensor). 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. If 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 misunderstanding something?

What surprised me a bit:
I once disconnected the LMM (lambda sensor) and drove without it - I would subjectively say that it even runs a little better without the LMM (but that might be my imagination) - definitely not worse. And when I drive with the LMM disconnected, 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 performance drop?


"After running for a while, 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. However, 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'm not sure how the control unit measures this.


I am grateful for any suggestions.

Regards,
Al.

Hello.

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

Da ich in dem Log was ich ansah keinen Überschwinger fand, evtl. mal die Länge der VTG-Verstellstange markieren (genau! Farbpunkt an Verstellmutter, Stangenlänge messen) und diese eine (!) Umdrehung kürzer machen. DanTest 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. It was replaced about 3 years ago. The shaft on that turbocharger had already been tampered with, as you can see from the damaged paint. Nevertheless, I installed it, but the performance remained completely unchanged. It was neither better nor worse.

"Today, I replaced the turbocharger again – this time with a refurbished 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. Additionally, I'm now getting the "limit exceeded" error intermittently at 2000-3000 RPM in 3rd and 4th gear when under prolonged full load."

I'm starting to feel a bit resigned.

Regards,
Al.

Hi,
Always go slow. What kind of exhaust cleaning system does the car have? Does it have an oxidation catalytic converter and an EGR system, or has a DPF (Diesel Particulate Filter) been retrofitted?
hg
Herbert.

@Herbert:
Yes, it has an aftermarket particulate filter installed by Remus... I also found this on the underside of the vehicle.

I even got the documents from the previous owner.
This is a Remus PMS-RS6. According to the records, it was installed 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,
Al.

Hi,
It's already clear that there's insufficient boost pressure (and therefore, not enough air being drawn in). You've tried and checked various things on the turbocharger side, but without any results.
"I'm now wondering if the back pressure in the exhaust system might be too high, and a retrofitted, clogged DPF could be a possible cause. I'm just putting this thought out there for discussion."
hg
Herbert.

Hi, that was my initial suspicion too... you read a lot about clogged 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 aftermarket 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 appeared to be quite open. However, I now suspect that the part further back in the housing doesn't have a finer structure.
I also once tried mounting the exhaust system to the turbocharger, using a spacer of about 10mm. However, I couldn't detect any noticeable difference.

Can the back pressure be checked using simple methods?


Furthermore, the question arises whether adding a catalytic converter would also significantly (or even much more) reduce the vehicle's performance at higher RPMs? Wouldn't the increasing exhaust flow also lead to a rise in back pressure? Or am I mistaken?

Regards,
Al.

@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 possibility that we should check?
Regards,
Al.

Hello,

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

Best regards, Rainer.