TDI Engine Problems: Black Smoke & Power Loss

Hello,

Octavia 1.9 TDI, manufactured in 1999 (previously driven 255,000 km without any issues).
Now, after replacing the mass airflow sensor (and thus restoring the airflow), the problem is that...
1. The vehicle emits visible black smoke throughout its entire RPM range, and even produces a black cloud when accelerating.
2. Sometimes, a hole can appear during the process of applying the coating.

"So far, visits to the workshop have only resulted in shrugs. That's why I bought an OBD diagnostic cable and read the error codes."

16485 - Mass Air Flow Sensor (G70): Implausible signal.
P0101 - 35-10 - - - Intermittent

After doing some research here and in other forums, I collected some measurement data (measurement blocks 3, 8, 10, and 11 /viewtopic.php?t=14540), but I can't interpret it. Can anyone help? Or what additional information do you need to provide an answer?

Thank you very much.

Hello.
Your mass airflow sensor is showing strange readings when your turbocharger experiences overboost during acceleration. In this situation, the measured airflow drops completely, and the engine enters a smoke-limiting mode.

The error you posted indicates that the LLM is having a connection problem. (This could be due to a poorly connected cable, a broken cable, or a loose connection).

Now the question is whether these drops in the main airflow actually exist, meaning whether something is temporarily leaving the air duct, or whether it's purely an electrical problem.
However, when I look at the graph of your boost pressure, it doesn't show the typical behavior you'd expect with overshoots.
After the initial surge, it remains below the target value. This is precisely the range where the LLM shows the drop.

Okay, let's check the electrical connections. If everything looks good here, then take a look at the air intake system leading to the turbo.
Who has any other ideas?

Best regards, Jochen.

Hi,

Original Bosch replacement mass airflow sensors have a sticker on them. Does yours have one? And how much did it cost?

Best regards, Rainer.

Hello everyone,

Thank you very much for the answers so far.

@Jochen_145: I hadn't even considered that possibility; I was actually focused on the AGR (Exhaust Gas Recirculation) or vacuum system. However, I couldn't find any leaks in the vacuum system. My next step would have been to have the AGR cleaned.
In this context, I recall having a persistent glow plug indicator light on once. The workshop interpreted this as a faulty brake pedal sensor, which was then replaced. Since then, it has only reappeared once after a 250 km highway drive at moderate speed (150-160 km/h), and it was resolved by turning off the engine and taking a short break. Doesn't the vacuum supply for both the turbocharger and the braking system rely on the same vacuum pump?
"Tomorrow, in daylight, I'm going to check the electrical wiring to the mass airflow sensor. Are there any outputs from VAG-COM that can be used for this check? Or could other measured values provide more accurate indications?"

@Rainer K.

The LMM (lambda oxygen sensor) was purchased new (November 2006) from ATU. I don't recall seeing a sticker on it at the moment, but hopefully, daylight will shed some light on that tomorrow. Should it be replaced again?

Oh, it cost around 85 euros.

Best regards.

Elblindo.

So, if there are no other copperworm error messages in the memory, I would say that it's quite clear that the intercooler system has a leak.

What kind of engine is this, exactly? It definitely looks like it has a wastegate turbocharger.

Sorry, I hadn't mentioned it before, but the engine is an AHF.
Regarding the requested label for the LMM, VEMO has a part with part number 10-72-0958, which also has an OEM cross-reference number.

I temporarily checked for leaks in the vacuum supply. I couldn't hear anything, but when you remove the engine cover, there's an oil layer visible on a part there (picture attached). /viewtopic.php?p=101088#101088

What is this component? And is there a connection to the error symptoms?

Thank you very much, as always, for all the answers.

Best regards.

Elblindo.

This is the connection for the 'blow-by,' which is the ventilation for the corrugated sidewall housing.

Here, the oil vapors from the KWG (presumably a specific system or device) are fed into the intake manifold for combustion.
Ideally, the connection should be tight, so that no oil leaks out.

If the connection is leaking, or if the connection is possibly damaged, the engine may draw in false air through this leak due to a large vacuum in the intake manifold.
This will not be measured by the LMM.

Actually, it's an explanation for your strange air mass behavior at full load.

Best regards, Jochen.

Please check your intercooler piping system for leaks. A hose runs from the turbocharger to a silencer, which is located in the wheel well and runs towards the front. From there, a short hose connects to the intercooler, and another hose runs from the outlet of the intercooler.
Check the rear edges of the LLK (likely referring to a component or part) for any oily residue.

Regards,
Malte.

Hello again,

since it already looks like...
"If it's dark, I'll do it tomorrow. After today's troubleshooting and inspection of the electrical connections of the mass airflow sensor (MAF), I cleared the error memory. So far, error code 16485 hasn't reappeared, and the acceleration issues and excessive soot production seem to be (subjectively) better."
I'll probably have to go back to the workshop. They had a manual air pump with a pressure gauge and used it to test some of the vacuum lines. They should definitely be able to repeat that test at all the relevant points.

I'll get back to you with any updates.

Regards,

Eblindo.

PS: Besides the FAQs, are there any other more detailed resources available to help with the interpretation of self-evaluated measurement logs?

PS: Are there any more detailed interpretation aids available besides the FAQs for the self-evaluation of measurement protocol data?

Hello.

oh, that's difficult..
I'm going to assert that the interpretation of measured values is possible through experience with engines and engine control technology. Therefore, you fundamentally need to know how an engine works, how it behaves under different load conditions, and how the engine parameters are adjusted.

You can find this information, for example, in the Bosch book about the diesel engine (Martin, what is the exact title?).

Once you understand these fundamentals, you can interpret the measurements you have taken.
Here lies the exact level of knowledge of the (expert) workshop, the competent master craftsmen, and the even more competent writers of this forum.

If you take some time to read through and study the examples here, it's not actually that difficult.
To my knowledge, there isn't a guide here that specifies how the curves should look in order for everything to be correct. However, I'm happy to be corrected if I'm wrong.

Best regards, Jochen.

Hello Jochen,

Thank you for the information. I had already suspected something like that (otherwise, how would misdiagnoses occur even in reputable workshops?).
Unfortunately, I don't have the time for in-depth study at the moment, so I'll probably continue to "burden" the forum with questions, as I find it to be excellent and knowledgeable.

Until the days...

elblindo

Hello elblindo,

I'm new here and I'm from Belgium. My native language is French, so please excuse any mistakes. I have an Audi 80 B4 TDI from 1994. I've had a similar problem before (black smoke in the rearview mirror and reduced power). I took it to a diesel specialist, and we agreed to replace the injectors first. The problem wasn't solved, so then they replaced the glow plugs. Finally, they found the issue to be with the flexible air intake hose after the turbo, the one located above the valve cover. There was only a little oil residue visible. The hose was torn at the bottom (cost €18 at VAG Belgium).
Good luck.

Best regards,
Roger

ps: Here's another forum in French with lots of photos and explanations about TDI engines.

http://www.forum-auto.com/pole-technique/section12/sujet298148.htm