2.7 TDI Turbo Problems: Troubleshooting Guide

Hello,
My 2.7 TDI engine, which doesn't have a DPF, is exhibiting strange behavior at engine speeds below 2000 RPM.
The increase in RPM in the lower gears is rather slow up to 2000 RPM, then it suddenly jumps. In the higher gears, the effect is less pronounced, but the engine pulls well within that RPM range.
When the accelerator pedal is set to a specific position, for example, 1/3 of its range in full-power mode, and the vehicle is, for example, climbing a long incline, the following behavior is observed: The engine speed increases, and after approximately 1.5-2 seconds, something noticeably changes in the control system, resulting in a noticeable jolt in acceleration.
Overall, it feels like a stiff VTG adjustment on my old AFN engine, where the pressure sensor took some time to activate the VTG linkage. However, this was only noticeable in the lower gears. Cleaning the turbo resolved the issue back then.
"Only in the 2.7 model is everything electronically controlled. The only component that seems to be controlled by vacuum is the EGR valve. Disabling the EGR valve increases torque slightly, but the underlying error code is still present."
In stationary operation, the charging pressure is correct, which is why the workshop says: everything is normal.
What could that be? Is there an additional boost pressure regulation system connected to the VTG (Variable Turbine Geometry) system of the turbocharger? Could it be the throttle valve located before the EGR (Exhaust Gas Recirculation) collector?

Just a note: The engine has been modified by MTM for increased performance. However, the effect was already somewhat present before, but not very noticeable.

I am grateful for any suggestions.

Greetings.

Andi.

Hello Andi,

It's best to check the mass airflow sensor (data block 4) and boost pressure control (data block 11) in the engine control unit using a diagnostic tool.

The mass airflow sensor is a likely candidate for causing problems, and the throttle body has caused issues in various 2.0 TDI engines.
I am not aware of any issues with the turbocharger boost control system in the 2.7L TDI engines, but this may be due to the significantly smaller number of vehicles equipped with these engines.

Best regards, Rainer.

See attachment.

Thank you for the initial feedback.

I forgot to mention one thing: when the engine is cold, the power delivery at low RPM is good. However, when the engine is warm, it becomes noticeably worse.
I've also noticed something else: between approximately 1400 and 2000 RPM, the following happens: when you press the accelerator, you initially feel like the engine is braking. Only after about 0.5 seconds does the engine start to accelerate again, with a slowly increasing power delivery.
"Everything is fine above approximately 2000 RPM. It's great for highway driving. However, it becomes annoying on country roads, and it's really frustrating in city traffic. Basically, you can drive in the city at around 1200 RPM, but if you want to accelerate, you should always downshift two gears. This is frustrating for experienced diesel drivers."

"That picture is great, where can I get something like that? Which holes are you referring to? To minimize the problem, I've currently reduced the EGR flow by using an aluminum plate with a 5mm hole. Without the hole, the engine check light comes on after a while. With the reduced EGR flow, the engine runs better."

I will be uploading data logs tomorrow. I brought my VAG-COM cable just in case.

Greetings.

Andi.

I am not aware of any issues with the turbocharger pressure regulation of the 2.7L TDIs, but this may be due to the significantly smaller number of vehicles.

With my limited knowledge, I can contribute to understanding this issue. The design of the loaders has been changed. Specifically, versions 2.7 and 3.0 have electromechanical adjustments. The VTG is no longer exposed to the pure soot flow. Unfortunately, the adjustment lever of the nozzle ring is still exactly the same as before, and it continues to rust and corrode. It seems that there is a certain wear/failure mode associated with the electromechanical adjustment. Letting it be without power for a while works wonders. Cleaning the adjustment lever of the nozzle ring also helps.

Well, the series of faulty actuators should really be identified by now.
They must have been phased out, as none of them should still be running with those 'old-fashioned' things.

It's also quite evident from the environmental conditions when an error occurs.
It could be due to the user, a faulty feedback mechanism, or a malfunction that prevents the system from reaching its limits.

Hello,

I have now recorded measurement curves in both cold and warm conditions.
In a warm state, one can observe, as expected, a significantly delayed increase in boost pressure.

What additional measurement data would be helpful in identifying the error?

He's no longer participating in the VTG Elektronik exchange program, which was also my hope.

I checked how easily the turbocharger's turbine spins. It's not spinning freely; there's some resistance. I once removed the turbo from my AFN engine with 180,000 km, and even that one didn't spin any easier.

How is it supposed to be normally?

The exhaust pipe that connects to the turbo is an aluminum manifold. However, there appears to be oil residue on the outside (which can be felt, but not seen). Does anyone have experience with this? Could there be a leak?

"Since the engine responds much better to the throttle when it's cold compared to when it's warm, I suspect one of the hoses in the charge air system. These hoses become much softer when the engine is warm, and there might be a small crack in one of them, allowing air to leak. However, I don't hear any whistling."

Can you check if the EGR valve is not closing properly when the engine is warm?

Greetings.

Andi.