Audi A4 3.0 TDI: Power Loss Troubleshooting

Hello fellow DIY enthusiasts,

My car, Berta, is no longer running as well as it used to . That means, it has lost power. It feels like it's missing about 50 horsepower.

It all started three weeks ago when my car, fully loaded, went into limp mode while driving uphill at 35°C (95°F) in the shade (there were no jolts or unusual noises).
Boost pressure below the defined limit.
Ignition on/off, it's running again, but with noticeably less power.
The turbo doesn't kick in until around 1600-1700 RPM (that typical whistling sound), instead of around 1400 RPM.
Below 2000 rpm, there's little acceleration; above that, the power delivery is stronger, but still less than normal.
There is no jerking or similar issues when accelerating.

Since then, the engine has sounded somewhat muffled, similar to when the DPF was full.
I used it outside today. The main cat looks good, and there's no excessive back pressure when I blow compressed air through it.

Previous errors/repairs:

December 2011: All 6 injectors replaced, as values were partially above -60ms, white smoke at idle, and misfires during warm start after a few minutes. -> OK.
May 2012: New mass airflow sensor installed due to slight performance loss. Calibrated -> OK.
August 2013: New battery.
July 2014: DPF (Diesel Particulate Filter) full -> regenerated, cleaned/flushed, differential pressure sensor replaced -> OK.
September 2014: Replaced the cylinder head and one injector after the injector burned a hole in the water jacket. Also cleaned the intake manifold and EGR adapter (the adapter was completely blocked) -> OK.
June 2016: Emergency mode, performance loss -> not applicable/not relevant.

So far, I have:
- Inspected the intake path up to the turbocharger -> clean.
- Checked turbocharger hoses -> no hoses loose or torn.
- LMM disengaged -> Subjectively, slightly more power.
- Subjectively, the turbocharger is performing as it did before, with no noticeable clicking or other issues.
- The VTG (variable timing gear) adjustment operates smoothly throughout its entire range, and is fully retracted even when the ignition is on.
- Actuator diagnosis for VTG (Variable Turbine Geometry), throttle valve, swirl flaps, AGR (Exhaust Gas Recirculation) valve, and AGR cooler: all OK.
- I blocked the EGR valve with a metal plate for a couple of days. Below 1400 RPM, the engine ran a bit better, but above that, it was the same as without the plate. After one day, an error code appeared in the error memory: "EGR return rate too low."
- The combined catalytic converter and DPF unit was removed and blown out with compressed air. Subjectively, there was no pressure buildup (the differential pressure sensor indicates 3 mbar at idle).

I noticed today that the loader on the open-air side is oily, and there's quite a bit of dust stuck to it.

I'm at my wit's end and hoping that one of you has a brilliant idea.
Thank you very much in advance!

I have attached a log with values ranging from 1000 to 4600 1/min.

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

"Micha"

Hi Micha, where's the car scan?

Hi Rainer,

Unfortunately, I didn't perform an auto-scan back then, but I only read the error memory of the engine control unit.
The attached car scan is from today.
I hope it helps anyway.

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

"Micha"

Hi, first things first: let's fix this.
/viewtopic.php?t=28354&highlight=p1018

mitch79 wrote:

I noticed today that the loader on the open-air side is oily, and there's quite a bit of dust stuck to it.

Inside the pipes/hoses or on the outside?
Innen ist normal, da die Kurbelgehäuseentlüftung die Öldämpfe in den Ansaugtrakt leitet. Siff außen wäre ein sicheres Zeichen für ein Leck in der Ladeluftstrecke, wodurch die ölige Ansaugluft entweicht anstatt im Motor zu landen. Dies isto fix.

Then, check if the other error reappears after deleting it and taking it for a test drive.

Best regards, Rainer.

Hello everyone,

First of all, I'm sorry for not getting back to you sooner, but in the meantime, a few other urgent matters have come up.

But: After trying and tinkering a lot, I found and solved the problem.
It was a (brand new, only 4 years old) LMM.

I swapped the swirl flap actuators between the cylinder banks, but the error remained on the same bank. I suspect a broken wire. I cleaned the connector and treated it with contact spray.

The oil traces are located on the outside, at the point where the crankcase ventilation connects to the charger, specifically on the intake side. I pressure-tested the turbocharging system, and only at this point did any air leak out.

Is there a risk to the engine due to the problem with the swirl caps?
Melted pistons or valves, or something similar?

Thank you very much for your support!

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

"Micha"

I'm not familiar with your engine. However, the swirl flaps should be okay, as permanent damage would occur if they were constantly closed. If they are permanently open, it will most likely only lead to increased emissions, as the swirling effect of the incoming air would be lost.

I would fix that.

Hello Mitch,

Here's what can happen due to faulty swirl flaps and injectors that don't close properly: /viewtopic.php?t=28772
The thread makes it clear that the damage is not solely attributable to the swirl flaps, but also to incorrect fuel injection.

Unfortunately, these two issues often occur simultaneously, especially with vehicles that have driven over 200,000 km.


P.S. Regarding the amplifier located in the rear of the car, on the left side, please check if there's any water in it. The hose that supplies the rear windshield washer nozzle is prone to coming loose, which can flood the amplifier.

Hello Matthias,

Thanks for the information. I'll start troubleshooting again in the next few days, and in the meantime, I'll try to drive more gently.

Hello Hufe,

You are scaring me.
I replaced the injectors 5 years ago, and the values have been fine ever since, and I check them every few weeks.

When I replaced the cylinder head 2 years ago, I didn't find any signs of melting on the pistons, cylinders, or valves; I guess I was lucky.

Is the amplifier located at the rear, on the left side? Is it hidden behind a panel?
The car scan only mentions the antenna amplifier, but the radio reception is always good. I haven't found any water anywhere inside the car. And this error has been there for a long time, at least since I started using VCDS.

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

"Micha"