1.9 TDI ATD: Power Loss & Soot Issues

Hello,

My ATD (presumably referring to an Audi TDI) is acting up a bit. Last night, while driving on the highway, I noticed that it was emitting some black smoke from the exhaust when I accelerated hard. At least, I could see the smoke trails in the headlights of the cars behind me.

Furthermore, I've noticed:


- Sometimes he seems "sluggish," but usually he's back to "normal" the next day.

- Sometimes, the instantaneous fuel consumption display shows approximately 90% and approximately 100% throttle positions on a flat road, but displays the same value. For example, at 90% throttle, it might show 18.5 L/100km for instantaneous consumption. If I then fully depress the accelerator, nothing changes, and it remains constant at 18.5... but this isn't always the case.


More important information:

- No idling fluctuations, no misfires.
- Fuel consumption figures (all-wheel drive!) with Climatronic always between 4.8 - 6.5 liters per 100 km.
- flawless starting.
- Virtually no measurable oil consumption (~0.5L / 30,000km).
- LMM is the first.
- 223,000 km mileage

I initially suspected the mass airflow sensor (MAF), as it's been there since the beginning... but it looks fine, with no deposits - and the VAG-COM readings don't indicate anything unusual; the actual values are usually slightly below the target values, but according to a technical article, this doesn't necessarily indicate a fault.

Do you have any more ideas?


What immediately comes to mind is a "sticking" EGR valve, which sometimes doesn't close properly – this would cause it to vent boost pressure into the exhaust system, leading to soot formation and a loss of power.


I'm ruling out faulty solenoid valves like the N75, as they should be recorded in the vehicle's fault system (FSP), right?



Greetings.

Octavia_4x4 wrote:

I'm ruling out defective solenoid valves like the N75, because surely they would be recorded in the fault storage (FSP)?

Only if the electrical values are outside the specified range.
For example, if the N75 valve is faulty, you might see error messages like "LD control difference sporadic" during severe LD control errors, but without a specific indication of the N75 valve itself.

Okay.

I learned something new again...

How do I check this? The boost pressure should be between 1000 and 4000 mbar at full throttle. But would a faulty N75 valve also cause the excessive soot?

Here's what comes to mind:


"When I turn the ignition on, I constantly hear a 'tick tick tick tick tick...' sound coming from the engine compartment, which seems to be the valve opening every second. This has been happening since I've owned the car, and that's only been for a few thousand kilometers."

Check if the air conditioning lines are chafed where they connect, and make sure no rodents have chewed on the hoses.

Best regards, Rainer.

Okay, the intercooler idea is a good one. I'll take the front of the car down this week for another reason, so I can check that at the same time. If that's the case, it would be completely full of oil...

The hoses are all okay, I've already checked them .


Is it normal for the engine to constantly adjust the target value for the N75 valve or the EGR valve?

Octavia_4x4 wrote:

Is the constant adjustment of the N75 or the AGR valve normal?

For the N75, the minimum duty cycle is usually 5%.
Probably the same applies to the EGR valve.

Okay, I'm going to log the AGR (Abgasrückführung), mass airflow sensor, etc. again today, and I'll check the coolant lines for leaks in the coming days.

I only want to replace the LMM if it's the cause of the problem.

Quote:

I only want to replace the mass airflow sensor

if it's the cause of the problem...
Do you also need that? Because with a standard engine control unit , it } cannot be the cause of constant smoke when accelerating to full throttle.

Well, what does "continuous smoke" mean...? If I accelerate quickly, I can see that the light behind me gets blurry... I can't really say how long it lasts, because I'm not driving behind myself .