Low boost pressure below 2500 RPM, Passat 2.0 TDI BMP

As mentioned above, I am experiencing this problem with a Passat.

I'm attaching the logs from KDataScope below.

The Passat now has 339,560 km on the odometer. Recently, all the PD injectors were replaced, and the seats were refurbished. The vehicle was shaking violently when accelerating.

My acquaintance then said that the engine runs very sluggishly at low speeds.

Based on the logs, it can be seen that the target pressure is insufficient in the lower speed range.

The AGR (Automatic Gear Recognition) system was deactivated via software, and the DPF (Diesel Particulate Filter) was also removed and deactivated.

What I still want to do is mechanically close the AGR valve and check the boost pressure control valve more closely.

Does anyone else experience this problem? It seems to be producing quite a lot of smoke.

Based on the values, I can exclude LMM.


Thank you very much.

Best regards, Felix.

Hi,

The overshoot of the boost pressure above the target value at approximately 3000 rpm, followed by an undershoot, could indicate a problem with the variable geometry turbine (VGT) adjustment mechanism of the turbocharger.
Given the currently high ambient temperatures, the build-up of boost pressure in the lower RPM range may be considered "state of the art" depending on the engine, so I wouldn't overemphasize it. Unfortunately, you don't mention the environmental conditions. It was over 30°C in the shade here yesterday.
As a meaningful measure at this current time, I would recommend checking the vacuum hoses for leaks, and inspecting all vacuum canisters and connections for leaks.
Also, check the intake manifold and the charge air hoses for any oily spots, and make sure that the exhaust temperature sensor, if present, is tightly screwed in before the turbocharger inlet.
Unfortunately, the mileage may indicate several issues that, taken together, paint a certain picture. The removal of the DPF is one of these, as it alters the behavior of the turbocharger's boost pressure regulation (and would require the turbocharger to be controlled differently).

Quote:

The AGR (Abgasrückführung) was deactivated via software, and the DPF (Diesel Particulate Filter) was also removed and deactivated. What I still want to do is to mechanically close the AGR valve, and to check the boost pressure control valve more closely.

Technically not really useful, and legally questionable. In my opinion, it would have been more sensible to invest the money and time in cleaning the DPF (Diesel Particulate Filter) and replacing the EGR valve (which typically doesn't last more than 300,000 km). It's nonsense to additionally seal the EGR valve, just like it is to remove the DPF.

Quote:

He probably doesn't produce a small amount of soot.

See my above sentence, overall it's now a completely nonsensical and messed-up thing, and as you can see, it doesn't work any better, but rather it smokes and pollutes the rear and those who follow.

Quote:

Based on the values, I am excluding LMM.

Depending on the software in the engine control unit, the mass airflow sensor (MAF) doesn't really play a role in boost pressure control under load. Therefore, the statement you made is meaningless without knowing the specific software. It's impossible to make a statement like that without examining the software.

Best regards, Rainer.

After my experienced runner (BKD) recently pointed out to me that he would like a new tandem pump (due to a significant amount of oil in the engine), it would also be possible for me to get one.
PDE wiring harness / fuel pump.
And that a turbo engine with over 300,000 kilometers can function properly... hmm, you don't hear that very often!
The rest was already thought of by Rainer!

Sure, here's the translation:

"Sg" is an abbreviation for "singular." It is used to indicate that a noun or pronoun is referring to one person, place, or thing.

For example, the sentence "The cat is on the mat" uses the singular form of the noun "cat." The sentence "He is my brother" uses the singular form of the pronoun "he."

In contrast, the plural form of a noun or pronoun refers to more than one person, place, or thing. For example, the sentence "The cats are on the mats" uses the plural form of the noun "cat." The sentence "They are my brothers" uses the plural form of the pronoun "they."

Oh, my mistake.

So, the log entry was created yesterday at 8 PM, with a pleasant temperature of 21 degrees Celsius. The intake air temperature was a high 42 degrees Celsius. According to his statement, the vacuum hoses were checked. Yesterday, I personally only checked the wastegate hose and verified that it was clear.

I still need to investigate further, but I thought I could rule out a leak in the charge air ducting because it's achieving the target values in the higher RPM range.


The turbocharger was replaced at 220,000 km. He had the infamous oil pump failure!

I am open to any advice .

Quote:

Yesterday, I personally just checked the wastegate hose and made sure it was clear.

Your turbocharger does not have a wastegate. To determine the functionality of the variable geometry turbine (VTG), the vacuum actuator must be unscrewed from the turbocharger, which can be a problem depending on the available space. When reattaching it, it's important to know what you're doing, as the mounting may allow for slight positional adjustments. You can't go wrong by making a small mark with a needle beforehand.

Even though it might work when the engine is cold, it doesn't necessarily mean it will work when the turbocharger is hot and there's excessive soot (your car is smoking).
The soot definitely indicates a leak in the charge air system.

Best regards, Rainer.

Oh my gosh, this is so embarrassing! For Michael.

But, it's not my car, I just took the matter into my own hands.

I will follow your advice and hopefully find the culprit.

To-Do:

Inspect VTG rods.
Inspect vacuum hoses for leaks.
Check the charge air ducts.

Are there any specific values in VCDS that I should pay close attention to? Including...? KDataScope Log?

I forgot something important; the engine sometimes goes into limp mode while towing, often with slight acceleration, but sometimes also without a trailer, especially when going uphill. Again, I couldn't reproduce the error yesterday. The error memory is therefore also empty.

If it goes into emergency mode, there will also be an error code stored in the system's memory, which should be posted here.

Generally, it goes into limp mode when the actual and target values are significantly different for an extended period (>=6 seconds?). Since the deviations you're experiencing only occur in the lower RPM range and are more pronounced under full load, the problem is less likely to occur without a trailer, and only happens during acceleration and for a short time. With a trailer, however, you will definitely find yourself driving at 2,000 rpm and full throttle for extended periods.

Today, I finally managed to focus on the details.

This morning, when I arrived at work, the machine displayed an error message indicating it was in emergency mode. Stopped the laptop immediately, but there's nothing in the error log.
But the emergency procedure was definitely a 100% success! No performance.

Okay, I've checked the boost pressure lines, and there's no hissing sound, and the pressure is holding.
Found a defective vacuum hose for the EGR valve, noted. Then I replaced the hose to the pressure sensor on the VTG (Variable Turbine Geometry).


VTG is doing well and is not struggling. And now I think I've found the problem, at least.

I always kept the basic settings running, but the VTG (likely referring to a valve timing gear) was adjusted incorrectly, and it was also operating at 90.3%. You could clearly see that the linkage was moving loosely. But only a disappointing increase in boost pressure.

When I apply suction to the pressure sensor with my vacuum pump, it works perfectly; the boost pressure increases!

Is the boost pressure control valve faulty now? Okay, so the hoses are sealed, with one hose running to the air filter and the other to the cylinder head.


Best regards, Felix.

Emergency mode activated, but no error codes? How were the EGR and DPF systems deactivated in the software, manually or through a software modification? When software is involved, it's likely that a variety of safety mechanisms have been disabled.

Have you ever measured the vacuum pressure at the N75 valve? If the pressure in the LD (boost) system doesn't increase significantly when the system is at its base setting, but does increase when using a vacuum pump, then either there isn't enough vacuum pressure available, or the N75 valve isn't functioning correctly. Measure the vacuum pressure at the inlet and outlet of the N75 valve using a vacuum gauge. The readings should be nearly identical in the low-pressure range.

Hi, yes, there's no mistake. What I saw when he deactivated the EGR valve was a map displayed. So professional, not just thrown together!

Okay, I'll do it now. Is the input VAC, and the output Out at the valve?

I was just looking at the service information from Pierburg. According to the documentation, the steering pressure should be a minimum of 480 mbar, but in my case, it's around 370 mbar. And the pressure that's supposed to be drawn off is 60 mbar, but I have 152 mbar.

And what pressure readings did he get at the valve inlet and directly at the vacuum pump?
If you have a vacuum pump, connect it to the VTG sensor. Create a vacuum of 370 mbar and observe how far the linkage is pulled. It should, of course, go all the way. I don't know if that vacuum pressure is sufficient.

Okay, the EGR cooler bypass valve is faulty. I couldn't draw any noticeable vacuum on the vacuum hoses, and when I checked the vacuum pump yesterday, I was surprised that it might be the pump itself. When I measured the pump itself without the T-connector, everything was fine, so I re-detached the hoses and checked them again.


If I disconnect the hose to the shift valve and block it, I will immediately create a vacuum, and the problem will be solved.


Thanks again for the advice, great forum!!!