Blue smoke on V6 cold start - cause?

Hello, I've already searched the forum thoroughly, but I couldn't find anything relevant to my problem.

My problem is the following: I have an A4 V6 2.5 TDI with the AKN engine. It's experiencing extreme blue smoke after a cold start and running roughly. I've taken it to the workshop several times, including the dealership, but without any results. The blue smoke occurs after every cold start, even in outside temperatures above 20°C, and lasts for about as long as it takes the engine to reach a temperature of approximately 65-70°C. The following things have already been done:
- Injection start verified.
- Turbocharger pressure measured.
- Preheating system checked.
- Oil separators cleaned and inspected.
- Recently replaced the camshafts, lifters, and rocker arms (new).
And about 4 weeks ago, the fuel injectors were also replaced on a trial basis (with used ones).
Despite all of this, there was no improvement. The oil consumption is zero; I drove approximately 35,000 km in two years using the long-life 0W-30 oil. The engine performance is also fully present even when the engine is warm, and the top speed is 230 km/h. I have also never had to top up the coolant; it has always been okay.

Has anyone else experienced a similar problem? Or does anyone know what might be causing it? And what would it cost to have the fuel injection pump checked by Bosch?

Oh yeah, the error memory is always empty.

If anyone has an idea, please let us know .

Regards,
Okay, I'm ready. Please provide the German text you want me to translate.

A log file from this state would be helpful (LMM, turbo pressure, fuel injection amounts). You could also check if the fuel injection timing is correct and within an acceptable range. Then, you can also check the coolant temperature sensor from the engine control unit and the other temperature sensors for plausibility.

If everything checks out, I'll have the compression checked.

Au00 wrote:

and about 4 weeks ago, the injectors were also replaced on a trial basis (used ones).

Did you at least have them checked beforehand? Mine were pretty worn out after 170,000 km. Now I'm seeing less blue smoke, but I haven't been able to check it properly yet when the temperature is low. However, it was never as bad as you're describing.

Let's leave the VP44 alone for now. Checking its condition costs approximately EUR 180.00, according to a post here. This price probably doesn't include removal and installation.

The LMM (likely referring to a Mass Air Flow sensor) is also a new part from last year, and the values are correct; I recently measured them and they were above 750. I recently cleared all the sensor data blocks while the engine was idling. Sorry for the unusual formatting; I'm not yet sure how to format it differently.

0:
032 069 000 017 106 213 059 112 161 102
1:
742 5.6 20.2 93.5
2:
742 0.0% 00100 93.5
3:
742 616.2 404.3 95.5%
4:
742 0.6 n OT 0.6 n OT 65%
5:
742 11.0mg 0.6 n OT 94.6°C
6:
0 km/h 00 00011 1.0
7:
53.1°C 103.4°C 55°C 94.6°C
8:
742 0.0mg 29.8mg 22.9mg
9:
0.0mg 99.0mg 0.0mg 99.0mg
10:
404mg, 1000mbar, 1081mbar, 0.0%
11:
742, 1050 mbar, 1081 mbar, 85.2%
12:
11111111 0.00s 13.07V 94.6°C
13:
-0.78 mg -0.55 mg
14:
-0.16mg -0.47mg -0.16mg
15:
742 5.3mg 0.8l/h 0.0mg
16:
48%
18:
13.22V 13.07V 00000000 0000
19:
366 0.5°v OT 22.1 54°C
21:
000 00000 10 0
25:
00005059 130 106CC150_1.V5A358494971
125:
Transmission: 1
ABS: 1

The mileage is only 112,000 km, and the injectors were replaced, with the previous set having only 90,000 km on them.

Is that diesel or oil?

Okay, I can't really do anything with your data like this. Also, the problem doesn't occur when the engine is at its operating temperature.

Data wiped? What about the trip log? Then you should have the data.

First, take a look at the temperature values in the cold state.

I can also perform a log flight, and I will then re-enter the data. The temperature values in the MWB 7 have a deviation of +/- 1° from each other, which I consider to be acceptable.

"Hi, I disconnected the diesel line from the second cylinder last week and attached a collection container, then started the engine (while it was cold), and the blue smoke was almost completely gone. The engine also didn't run much rougher than usual. Now my question: Could it be that the piston rings are already worn out at 114,000 km? The compression on the second cylinder is the lowest. The engine doesn't consume any oil; I drive about 30-35,000 km without ever needing to add oil, and there's no diesel in the oil. Last week, I tried to find a workshop in the area that could perform a pressure test on this engine, but I had no luck."

Best regards,
Okay, I'm ready. Please provide the German text you want me to translate.

Now, my question: Could it be that the piston rings are already worn out at 114,000 km? The compression on the 2nd cylinder is the lowest. The engine doesn't consume any oil; I drive about 30-35,000 km without ever needing to add oil, and there's no diesel in the oil.

How do you know that the compression is the worst? Just because the correction value displayed by VAG COM is higher? However, it could also be that this particular injector is faulty, and most of the fuel in that cylinder is evaporating instead of burning.

After starting, it produces blue smoke because the catalytic converter hasn't reached its operating temperature yet, and it allows unburned hydrocarbons (especially evaporated fuel) to pass through the exhaust.

No, I measured the compression using a compression tester, and the results are as follows: 1st cylinder - 28 bar, 2nd cylinder - 24 bar, and 3rd to 6th cylinders - 30 bar and 31 bar respectively.

Isn't cylinder 2 already below the minimum?

He's right at the limit now, but what's surprising is that he's not using any oil. If the piston rings are that worn, he should be burning oil, right?

Try this: Put some oil into cylinder 2. Then, immediately perform a compression test. If the compression is higher, it's likely due to the piston rings.

Otherwise, what was the condition of the valve guides and valve lifters before the replacement? We don't want a valve to be slightly damaged and the head to be blamed.

Don't immediately blame the piston rings! If you have poor compression readings, I would suspect the valves more readily, even with relatively low mileage.

The logic here is: lower compression pressure -> lower compression end temperature -> longer ignition delay -> incomplete combustion -> higher HC emission values (blue smoke).

It behaves similarly when you've used vegetable oil, as that also has a longer ignition delay. Mine smokes slightly blue even when warm at low load, despite the new injectors, and has a mileage of 83,000 km. However, the catalytic converter is not installed.

Hello,
I've likely found the cause of the blue smoke. Two connecting rods are bent, and the one from the 2nd cylinder is so severely bent that it's visible to the naked eye. The top dead center (TDC) point in the 2nd cylinder has been shifted downwards by approximately 2.5mm.
Looking for 2 used or new connecting rods, model AKN. Audi unfortunately only sells them in sets, not individually.

Best regards,
Okay, I'm ready. Please provide the German text you want me to translate.