Carbon Buildup in 2.5 TDI Intake Manifold (BDG, EU4)

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 perhaps only as wide as 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 them in WD-40 helped.

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 wonder 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 previously had an AEL and before that an AFN. With those engines, the intake didn't look nearly as bad. Everything was 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 highly dependent on the driving profile; a high AGR (Abgas Rückführung) activation 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 for a car than driving 200,000 km mostly on the highway with heavy loads.
The only way to legally prevent or reduce this is by adjusting your driving habits.
Otherwise, you can mechanically block the EGR valve.
Best regards,

Hi

As mentioned, AGR is initially being 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 warning light didn't come on then.

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. I haven't been able to find any leaks so far.

hi

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

I'm sorry, but I cannot access external websites or specific files online. Therefore, I am unable to translate the text from the provided URL.

I watched that video years ago, and I immediately took action. I checked my intake manifold, and the inside looked brand new.
fact: the ball was already installed by the previous owner in the vacuum hose (which works well without issues on older AEL models). That's also why there were no noticeable problems.

Quote:

A 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. They won't clear themselves while the engine is running.
hg
Herbert.

Hi Herbert,
He cleaned the airways (as much as possible, meaning mostly?). Therefore, 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, and of course, it depends on how much oil the turbocharger bypass valve (ATL) allows through: the more, the faster. A turbocharger bypass valve (ATL) that theoretically operates without any oil leakage into the intake manifold would, of course, not contribute to the removal of carbon deposits.
haithamina

Hi,

I also own a BDG, and I'm experiencing the same issue.
Everything is completely clogged with black sludge. There's also about 5mm of it in the suction hose.
Did you lower the interest rates offered by both banks?
Is it crumbling or peeling off in chunks, or is it coming off in a smooth layer?
Mine has only 154,000 kilometers on it.

Quote:

The oil mist will slowly but surely remove the carbon deposits. This has been described many times here, and it makes sense due to the properties of 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. There's also about 5mm of it in the suction hose.
Did you lower the interest rates offered by both banks?
Is it crumbling or peeling off in chunks, or is it coming off in a smooth layer?
Mine has only 154,000 km on it.

I removed them from both benches.
Parts of the material are flaking off and peeling in strange ways, about 5mm thick, especially near the AGR valve connection. I nearly crashed because nothing was flowing through anymore.

Today, of course, the check engine light came on. I wonder why .
I'm going to have to 'fix' this. It's not working like that.
Once that's done, I'll take everything apart again, disassemble the heads, and clean them thoroughly.
You definitely can't get that kind of debris into the swirl chamber. And nobody wants to just throw the dirt directly into the combustion chamber.

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

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

Herbert wrote:

Quote: The oil mist will slowly but surely remove the carbon deposits. This has been described many times here, and it makes sense due to the properties of 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 ask about this again. Does your engine start well? I sometimes have problems if I haven't driven the car for a few hours; I have to really crank it. During the compression test, it turned out that the left bank (relative to the direction of travel) is continuously losing compression. Could this be related to the sludge?"

I need to check that too. 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 started. 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.
Look at this: https://community.dieselschrauber.org/en/viewtopic.php?t=23461
It explains how I fixed my starting problems.

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

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

I also tried to clean it in my B5 MKB 1Z.
In my opinion, any attempt to use chemicals is inappropriate; it can only be fixed properly through mechanical means.
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 injection engines while they're running.

exciter wrote:

...should function directly into the diesel injectors during operation.

And then the VTG (Variable Turbine Geometry) 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?