Extreme carbon buildup in the intake manifold of a 2.5 TDI BDG engine with Euro 4 emissions standard

Hello fellow diesel mechanics,

Today, I disassembled the suction pipe and the shut-off valve to adjust the pump and perform a minor inspection.
What I saw there absolutely shocked me.

Inside the aluminum housing where the AGR (Abgasrückführung - exhaust gas recirculation) air is fed, the two channels leading to the cylinders were completely blocked. The opening was probably no thicker than my index finger!
A crust, approximately 0.5 cm thick, has formed all around.
The long pipe leading to the cylinders didn't look any better. The intake manifolds themselves were completely clogged.

Okay, everything has been disassembled, and cleaned as best as possible.
The pipes looked better, but in the end, I looked like a chimney sweep.
I couldn't get them 100% clean. But soaking it with WD-40 did the trick.

Okay, I've temporarily disabled the AGR (Abgasrückführung) system to give the oil mist in the intake manifold a chance to gradually remove the remaining residue.

Now I'm wondering where all this excessive soot is coming from.
The car is from 2003, has 240,000 km on the odometer, and has a complete service history with Audi (who replaced the timing belt and marked it with Edding pen).
I used to have an AEL engine, and before that, an AFN. The intake looked nowhere near as bad as it does now. It was all just minimal...
The box was completely full.

What can generally be done to address deposits?
What is the best way to prevent it?

Best regards and thank you in advance.

It's heavily dependent on the driving profile; a high AGR (Abgas Rückführung - Exhaust Gas Recirculation) rate naturally leads to more soot entering the intake manifold, which consequently causes more deposits to form.
Driving a lot in the city is worse than driving 200,000 km mostly on the highway with a heavy load.
The only way to legally prevent or reduce this is by adjusting your driving profile.
Otherwise, you can mechanically block the AGR valve.
Best regards,

Hi

As mentioned, AGR is temporarily deactivated for testing purposes.
Of course, it's now running a bit rougher when idling, and it's only a matter of time before the engine check light comes on.
I had it running for 10 minutes earlier and drove 15km. The lamp hadn't arrived yet.

A positive aspect is that, subjectively, the engine runs better without the dirt accumulating in the pipes.
Let's see how things will be in the next few days.
I need to check the intercooler piping again. When I have the window open, it sounds like there's a leak somewhere. So far, I haven't been able to find any leaks.

hey

"Even with AEL, these problems may occur (or could occur). Are you familiar with this technical article?"

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

I watched this a long time ago, and I took action based on it. I did an inspection, and the inside of my intake manifold looked brand new.
fact: the previous owner had already installed the pressure sensor in the vacuum hose (which works well on older AEL models without any issues). That's why there were no anomalies.

Quote:

The positive aspect is that, subjectively, the engine runs better without the dirt in the pipes.

Quite likely subjective. The intake channels in the cylinder head are still blocked. That won't just disappear on its own within the company.
hg
Herbert.

Hi Herbert,
He cleaned the channels (as thoroughly as possible, meaning mostly?). In that case, it's possible that he's now breathing better.
The oil mist will slowly but surely remove the carbon deposits. This has been described many times here, and it makes sense given the properties of motor oil. Of course, it depends on how much oil the Automatic Transmission Fluid (ATF) is carrying: the more, the faster. A (theoretically) oil-loss-free ATL (Air-to-Liquid) system would, of course, not eliminate the need for removing oil residue.
I am unable to translate "haithamina" because it does not appear to be a word or phrase in the German language. It may be a misspelling, a proper noun, or a term from a specialized field. If you can provide more context or clarify the intended meaning, I would be happy to assist you with the translation.

Hi,

I also own a BDG, and I'm experiencing the same issue.
Everything is completely clogged with black sludge. Approximately 5mm in the suction nozzle as well...
Did you lower the interest rates offered by both banks?
Is it crumbling or creating a smooth surface when it's removed?
Mine has only 154,000 kilometers on it.

Quote:

The oil mist will slowly but surely remove the soot deposits. This has been described many times here, and it makes sense due to the capacity of the motor oil

.
negative.
hg
Herbert.

Hi,

I also own a BDG, and I'm experiencing the same issue.
Everything is completely clogged with black sludge. Approximately 5mm in the suction nozzle as well...
Did you lower the interest rates offered by both banks?
Is it crumbling or creating a smooth surface when it's removed?
Mine has only 154,000 km on it.

I took them off both benches.
The material is flaking and peeling off in strange places, about 5mm thick, especially near the AGR valve connection. I almost crashed. Nothing was working anymore.

Of course, the check engine light came on today. Why, I wonder,
I'm going to have to 'fix' it. It's pointless.
Once that's done, I'll take everything apart again, disassemble the heads, and verschandeln them thoroughly.
You definitely can't get into the 'Drallkanal' like that. And nobody wants to just throw the dirt directly into the combustion chamber.

Sure, here's the translation:

'MFG' is an abbreviation for 'Mit freundlichen Grüßen,' which translates to 'Sincerely' or 'Best regards' in English.

Herbert wrote:

Quote: The oil mist will slowly but surely remove the soot deposits. This has been described many times here, and it makes sense due to the capacity of the motor oil . negative. hg Herbert

, right, I've already been trying that for 70,000 km on my T4 without any success.

I need to chime in here as well. Does your car always start easily? I sometimes have problems if I haven't driven the car for a few hours; I often have to really crank the engine. The compression test showed that the cylinder bank on the left side (facing forward) is continuously losing compression. Could this be related to the sludge?

I need to check that again as well. Does yours always start well? I sometimes have problems if I haven't driven the car for a few hours. I have to really crank it to get it going. The compression test showed that the left bank is continuously losing compression in the direction of travel? Could that be related to the sludge?

May, but doesn't have to.
Check this out: /viewtopic.php?t=23461
It describes how I fixed my starting problems.

Sure, here's the translation:

'MFG' is an abbreviation for 'Mit freundlichen Grüßen,' which translates to 'Sincerely' or 'Best regards' in English.

I also tried to verschandeln it in my B5 MKB 1Z.
In my opinion, any attempt to use chemicals is inappropriate; I believe the problem can only be resolved mechanically.
Maybe a sticker that reduces air circulation would be the best solution .

I have a spray from Kent called "One-Shot," which is a carbon solvent. I'm going to try it on the intake manifold. Apparently, it's supposed to liquefy carbon deposits and feed them into the combustion process, and it's supposed to work for diesel direct injectors while the engine is running.

exciter wrote:

...is supposed to function directly into the diesel injectors while the engine is running.

And then the VTG gets stuck in the turbocharger, and the catalytic converter gets clogged with the sludge?!
I don't think it's a good idea to let something like that go through the entire engine.

Will it burn?