VW Passat 2.5 TDI: Power Loss & Noise Issues

Hey everyone,

'We've been experiencing the same problem with our two identical Passat cars (2004 BDH sedan, 220,000 km) for quite some time, and so far, no one has been able to identify or fix the issue. I recently purchased VCDS and hope that you can help me.'

The problem is an intermittent hissing or 'fluttering' noise in the range of 1700-2300 rpm, which originates from the turbocharger and is apparently called 'kaudern.' However, based on extensive research, I am quite certain that the cause lies elsewhere. This is because, firstly, the turbocharger in this Passat was recently replaced (and it was suspected as the source of the noise due to its location), and secondly, all other parameters seem to be normal.
Both Passats received a power increase. In one of them, the noise was already present before (although to a lesser extent), while in the second, it appeared shortly after. As mentioned, since this noise was already present in one of the Passats and gradually became more noticeable, and now a new turbocharger has been installed, I can rule out overloading of the turbocharger. Instead, I suspect that the air cannot escape quickly enough, which causes this 'rupturing' of the air against the turbine blades and thus the roaring sound.
'About 2 to 3 years ago, this issue only occurred when going uphill under full load. Now, with the Passat and its new turbocharger, it can be noticed even while driving straight, and also during gear changes. It has become more noticeable since the turbocharger was replaced, likely due to its improved function. This Passat, with its new turbocharger and more pronounced roaring sound, also lacks proper power. I will try to perform a measurement tonight and post the results later. Besides the noise and the loss of power, there are no other symptoms, such as excessive smoke or soot production, and there is no noticeable increase in fuel consumption.'

'If you find anything in the logs that suggests excessive backpressure or a defect in the engine, ESP turbo, etc., please don't hesitate to point it out. The same applies to any other suspicion. For example, we can rule out a blocked crankcase ventilation system because there is no hissing sound when opening the oil filler cap, and the cap doesn't bounce. Also, as far as I know, the BDH (presumably referring to a specific vehicle or component) has a cyclone separator installed, which shouldn't cause many problems.'
What seems strange about the parameters is that the boost pressure is significantly higher than it should be. And the EGR valve reading is constantly at 88; shouldn't this go to zero when accelerating fully?

Thank you very much in advance!

Hi,

Your boost control system isn't working; is your "new" turbo perhaps such a "rebuilt piece of junk"? That's actually normal (that it's junk and doesn't work properly).
Unfortunately, there are far too many people who assemble low-quality products using spare parts from East Asia.
Therefore, always buy replacement chargers from a reputable parts dealer; they are much cheaper than at the and, above all, they work.

Otherwise, hissing or whistling noises can indicate leaks in the charge air system, which is even more likely due to the malfunctioning boost pressure regulation.

"Furthermore, it seems like your engine tuning in the ECU is a bit strange, or the mass airflow sensor (MAF) might be defective. At 2000 rpm, the actual boost pressure, target boost pressure, actual air mass, and the air mass-related speed limiter are not consistent with each other."
Testing a new LLM.

Best regards, Rainer.

Thank you for your reply!

The turbocharger should definitely NOT be a Chinese-made unit – it's from **************, which specifically advertises that they only use original parts. Furthermore, this problem already existed before the replacement; the noise was the reason for the replacement in the first place, but it didn't help. The tuning did NOT make it louder; in some Passats, this issue has been present for several years, even before any modifications, and it hasn't become more noticeable immediately after the tuning. It only developed gradually over a long period.

Perhaps the photos will help identify the charger. At least the compressor housing is a Garrett part, and the turbine and compressor wheels also have only minimal play, which is reportedly necessary according to the website.

'How do you determine if a tuning is unusual, and what values indicate this?'
I can swap the LMM from the other Passat; it was already replaced once, also unnecessarily. Back then, the suspicion was that there wasn't enough air mass (it should probably be higher than 1000mg, BEFORE tuning), but afterwards it was exactly the same... All three should actually be fine, THEY SHOULD.

The system has already been checked for leaks three times. A leak should typically cause a 'normal' hissing sound across the entire RPM range, or is it possible that it only occurs within a relatively small range and is also intermittent rather than continuous? The sound is similar to what can be heard in the audio file.

[Dateien sind im Posting mit hochzuladen!Bitte gib mir den deutschen Text, den du übersetzt haben möchtest.

Can this also be tested yourself, for example, by closing a specific opening and seeing if any 'outside air' is being drawn in?
Thank you very much and best regards!

Quote:

The turbocharger should definitely NOT be a Chinese-made charger; it's from **************, which specifically advertises that they use ONLY original parts.

As the saying goes, "Every day, someone makes a mistake." The fact that the price for a new turbocharger is about 50% higher everywhere else should certainly give you pause for thought.
That's why you also install a refurbished loader.
Because you're taking the risk of getting a faulty or tampered-with loader for just 200 euros, which has probably had some replacement parts and a quick clean. After all, what else would you have to do?

"Back in my chip tuning days, I had to deal with potential customers and their broken-down cars quite a few times – maybe two, three, four, or even five."
After every single test drive yielded negative results regarding tuning modifications, I started to wonder what I was doing, essentially offering free testing services for people's cobbled-together junkers, wasting valuable work time only to earn absolutely nothing (0 EUR).
After that, I simply sent everyone with such junk away, and since then I haven't had any more problems, and most importantly, I have appointments again that bring money into the company.

Anyway, your boost pressure control isn't working. If you had installed a new turbocharger, you would know that the problem doesn't lie there. } So, you have to figure out what's going on.

Check:
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.

Best regards, Rainer.

'Excuse me, what gives you the right to insult me like that? You know less about me and my life than you do about the universe – which is probably something you've heard of. I wouldn't even believe that we know each other or have spoken for just one second!'
I'm sorry that I don't have €800 to buy a new one. Maybe I should just let VW diagnose and repair the problem for €3000, instead of paying you €400 for your software and then being treated like this.
Are you also offended when you reach out to someone who is supposed to help you, simply because you are not familiar with the field?

Furthermore, did you even read my problem description carefully? All the issues were already present BEFORE the turbocharger was replaced. Also, the performance loss was exactly the same. What is the probability that a new turbocharger, due to inferior quality, would IMMEDIATELY fail and cause EXACTLY the same problems, without any deviation, as two previous turbochargers after approximately 200,000 km and 170,000 km?

When I ask you how you conclude that the LD regulation doesn't work, or that the tuning is nonsense, or that the LM has failed, I receive no response. Instead of providing an answer, you resort to insults and imply my ignorance (which is partly true, as it wouldn't be necessary for me to seek help if it weren't!). You fail to address my questions in any way, preventing me from learning anything.

Furthermore, in beautiful Germany, some ATL units cost significantly less than €325; I've found plenty for under €300 – so that figure is simply nonsense. Considering they get the entire turbo unit back, most of which likely have no real damage, why wouldn't it be possible to repair it for €325? And why would others cost more? Perhaps because it's just outrageous? What would I do with an ATL costing €600 when I can get a brand new one for €800?

Don't you think I'm trying to figure out what's going on? As I mentioned, I specifically bought VCDS so that I could have some influence myself and not always have to rely on incompetent dealerships and workshops. You can see what kind of results that leads to...
Since you're saying that with a decent turbo, I would at least know that it's not the problem, it means you're not really sure what the cause is. What else could be considered?

By the way, I still have the old turbo here. So, maybe we could take it apart and compare it to yours (or yours) to try and identify or rule out the problem?

Okay, if you don't want to help me, that's fine. No one is forcing you to waste your valuable time with me, this complete idiot and cheapskate... But as far as I know, this is a free forum, and in forums, people write without expecting payment.
However, if you decide to post something, wouldn't it be much more helpful to provide useful answers instead of insults? Because so far, your 'efforts' have achieved absolutely nothing, and on top of that, you've wasted your own time.

I'm not insulting anyone; I'm simply describing how reality is. The fact is that every day, there's someone who buys a faulty charger instead of one that is guaranteed to work as it should. A new charger usually costs less than 800 EUR, except for the .
"Sure, there are some providers who can get the charging settings right, but that takes time and therefore money. The majority of these "tuner" shops are simply amateurs who are tough enough to ignore complaints. If it were otherwise, I certainly wouldn't have sent any potential customers away with such substandard work."

It's up to you whether you learn something from this or give up because you can't bear the truth.

You write so much, please answer my question: Where can you be sure that the charger is working and its settings are correct?
a) New part from the manufacturer (as it is installed in new cars).
b) refurbished used parts.

Next question: Considering the effort involved, is it worthwhile to install option b) and risk the possibility that the boost pressure regulation behaves like it does now for you, leaving you just as clueless about the source of the problem as before?

Here's how you can tell that your boost pressure control system isn't working: The actual boost pressure reading, as measured by the boost pressure sensor, is stuck at the maximum value of its range, 2570 mbar. It's likely even higher than that, but the sensor simply cannot display anything beyond this limit. The desired boost pressure, which is what the engine control unit (ECU) would ideally like to achieve, is significantly lower.
When comparing an old turbocharger to a new one, it will be difficult to visually determine if there is a problem unless there are obvious defects. Even a change of just 1mm in the length of the VTG adjustment rod can have noticeable effects. It's impossible to tell by simply looking at the vacuum actuator whether the springs and rubber membranes inside are identical and not defective.

Please familiarize yourself with the concept of a feedback loop. In short, it's a system where an actual value is adjusted to achieve the desired target value as closely as possible.

Quote:

I'm sorry that I don't have €800 to buy a new one. Maybe I should just spend €3000 at VW for troubleshooting and repair, instead of leaving €400 with you for your software and then being treated like this.

I'm telling you, if someone doesn't have the money, they wouldn't put a six-cylinder engine in a mid-range car, especially not one of those types where you can easily spend several thousand euros on it without even tuning it, simply because it's a terrible engine (a money pit).

It has been known for many years that the 2.5L V6 TDI engines have various problems which can be very expensive to fix; there are countless discussions about this online. You won't get far with just 3000 euros...

Even during the login process, you were informed multiple times about the function of features like boost pressure regulation and mass airflow measurement, as indicated by the links (technical articles) above in https://community.dieselschrauber.org/en/viewtopic.php?t=10163.
Your question about LMM -> LMM technical articles. The helpful answers were right in front of you from the beginning.

I would start by checking the basic settings of measurement block 10 or 11 in the engine control unit and see if the VTG lever switches quickly and smoothly between both end positions. If the new turbocharger is incorrectly configured regarding the VTG (or uses an unsuitable vacuum actuator), I'm concerned, as it would be too complicated to describe without a fundamental understanding of the boost pressure regulation system.

Furthermore, the VTG (Variable Turbine Geometry) pre-adjustment in the chip tuning data may be incorrect if, during full-throttle acceleration in the highest possible gear, the turbocharger pressure is regulated after a few seconds, but otherwise it is always too high or too low. In this case, either the VTG pre-adjustment is not correct, or the VTG itself is experiencing mechanical issues.

If your chip tuning was done correctly, the mass airflow sensor (MAF) will release the fuel injection amount that is normally limited by the torque limiter. If the fuel injection amount released by the MAF at full throttle is lower than the torque limiter setting, then either the programming is incorrect, or the MAF sensor is faulty and measuring too little air, or the actual airflow through the engine is too low (e.g., due to a tilted catalytic converter, worn camshafts, or insufficient boost pressure).

Please search the forum for your engine code, which is BDH.

PS: When you've calmed down again, hopefully you will realize that a few things here are actually correct.

So, I must say that repeatedly and deliberately calling someone 'stupid' in a few sentences IS offensive. Especially when you, as previously mentioned, know absolutely nothing about me. If you see it differently, then we probably had very different upbringings. Because there are easily estimated to be 100 other ways to express the fact that buying a cheap loader might not have been the best decision.

I don't want to disappoint you, but at , it probably costs twice the mentioned €800. The only 'store' I found that sells the matching charger NEW is currently offering it for €726, but the price fluctuates and it has also been close to €800. Whether you believe me or not.

I'd also like to inform you that we've both owned Passats for 12 years; they weren't simply bought for the fun of modifying them. And thankfully, in those 12 years, there haven't been any major problems. You often read that they shouldn't cause excessive trouble with proper maintenance, and at least in our case, that has been true so far. Perhaps it's time to put aside your prejudices about me and my intentions and ask questions next time instead of simply making assumptions?! It might not concern you, but maybe I can help dispel some of your biases, which are really getting on my nerves – I have serious lung problems – you can probably imagine that I'm not exactly rolling in money, and the cost of VCDS was already enormous. And instead of receiving any helpful assistance, I also have to listen to your negativity.

Your questions are funny, but unfortunately, they're completely useless. Give me the €726 plus installation costs, and I guarantee I will choose the safest option available.

Without knowing you personally, I'd say that you make hundreds of decisions every year that can't be described as '100% certain.' If everyone only made decisions that were considered absolutely safe – aside from the fact that we don't always know what is truly safe – people like you would probably struggle to survive, because there wouldn't be anyone around who needed help.

You always assume that I did everything deliberately and was fully aware of the consequences – have you ever considered that I'm not a professional and simply trusted someone? It probably never occurs to you.

I had already read those articles long before the first post here. Unfortunately, reading them doesn't immediately turn you into a professional who can identify and fix every mistake within seconds.

I'm going to test the VTG right now. Regardless of the result, do you think I should at least try to return the loader?

Because the threshold of 2570 mbar was not always reached with the old system. I simply assumed it was working better, even though it seemed strange that the value was significantly above what it should be. Therefore, I assumed there was excessive back pressure causing the problem.

Best regards,

Quote:

Regardless of the outcome, do you think I should at least try to return the loader?

It's a mixed bag, as I said, my experience is that it's almost always junk, but that doesn't necessarily have to be the case. The problem is that with the loader, you're introducing an additional potential source of error, because you can't be sure that it will work.

How are you going to argue that? Probably, the charger isn't working correctly?

Therefore: First, check if the valve travel gear (VTG) is moving properly in its basic operating mode.
If no: Check the vacuum sensor and manual adjustment; refer to the VTG technical article. If the VTG never or always engages, there is likely a problem with the vacuum connection or the solenoid valves: check the vacuum system as described in the technical article.
If so: There are several possibilities why the VGT (Variable Geometry Turbine) is not working correctly. The turbocharger control unit may be incorrectly configured (please DO NOT adjust any settings, including the end stops), the chip tuning data may be controlling the turbocharger incorrectly, or the solenoid valve that regulates the vacuum for the VGT may be intermittently malfunctioning.

Okay, here's the translation:

"Something else:"

Quote:

The same

problem with our two identical Passats}.
Does the turbocharger pressure control system not work correctly in both Passats, meaning is the actual boost pressure too high? If so, then chip tuning is very likely the source of the problem, especially if the cars are identical.

Okay, the VTG rod moves quickly, but not very much, it seems. It should be about 1 cm, but I think it's more like a maximum of 5 mm. However, this is in the cold state, which shouldn't matter. Does this indicate an incorrect setting?
The linkage on the old turbocharger also moved smoothly (as confirmed by disconnecting the vacuum hose at that time), and it was exactly the same amount, about 1 cm.
I have attached 2 pictures; after all, I might misinterpret it.

I would argue that the higher turbocharger pressure, which didn't exist in the older model, and the louder noise, which wasn't quite as extreme before, are contributing factors.
And now, possibly also due to the rod or shaft.

Thank you and best regards.

The vacuum hose on the canister looks somewhat weasel-proof, but not very reliable.

You can connect a hose directly to the vacuum pump and apply the vacuum to the canister; the adjustment range needs to be approximately 1 cm.

Check if the adjustment rod moves further out when the engine is off compared to during the actuator test. Make sure the hoses aren't connected incorrectly, that the corresponding solenoid valve isn't defective, or that the ventilation system isn't blocked by the vacuum system.

I have now gained some new 'insights.'

The rod cannot be moved further even when the engine is off; it simply stops. The movement is at most 7 mm; I marked a fixed point with a permanent marker and measured it. With careful measurement, it's a maximum of 7 mm, more likely around 6 mm.
Compared to the second Passat, it's very clear that the turbocharger on the new model protrudes much less. However, shouldn't it primarily provide too little boost pressure at low RPMs, rather than too much?
As I mentioned, the other Passat has the same noise and performance issues, although not to the same extent, DESPITE the VTG adjustment appearing to function normally! However, this one doesn't have the excessively high LD (LD = Luftdruck - air pressure) of 2570 mBar. I'll gladly provide a log file from the second car if you'd like.

Since the rod cannot be moved manually either, is the test with the vacuum directly from the pump now unnecessary? If not, how should I proceed? Unfortunately, I don't know where the pump is located, and I haven't been able to find it using Google or the forum search. Is it that part behind/next to the coolant expansion tank?

Best regards,

Quote:

Compared to the second Passat, it's very clear that the turbocharger on the new model protrudes much less far out.

But wouldn't that primarily mean it delivers too little boost at low RPM, rather than too much?

Quote:

Extended rod or vacuum sensor activated: low boost pressure. "Short stroke or retracted into the vacuum chamber: high boost pressure." If the loaders are identical, then naturally the adjustment range and the default position of the adjustment lever must also be the same. What matters is not how the actuator rod looks or how it's assembled, but rather in which position the VTG (Variable Transmission Gear) adjustment lever is located at the bottom.

Since the rod cannot be moved manually either, is the test with the vacuum directly from the pump now irrelevant? If not, how do I proceed? Unfortunately, I don't know where it is located, and I haven't been able to find it using Google or the forum search. Is it that part behind/next to the coolant expansion tank? }
Trace where the vacuum hose from the pressure sensor on the loader is connected and review technical articles related to VTG (Verband Verkehrstechnik Güter) hoses.

Exactly, and that's the problem, right? The stick protrudes too far out of the container, and it doesn't move enough?
At least it goes further than the second Passat with the original turbocharger.

The adjustment lever is positioned slightly lower in the 'default' position on the new one, yet it retracts much less into the container. Does this 'lower' position mean that the internal mechanism of the valve is reacting differently or incorrectly?

Just for clarification (not because I don't want to do the work), but if the rod can no longer be moved even by hand, wouldn't it be possible that there is a problem with the vacuum system?

Best regards,

Quote:

Just for understanding (not because I don't want to do the work), but if the rod can no longer be moved even by hand, wouldn't it be possible to rule out a fault in the vacuum system?

If the two chargers are identical (according to the nameplate), then yes. If I remember correctly, there were different VTG control rings depending on the charger revision, but I no longer recall whether this applied to the motor.

Happy Sunday!

Most of the information on the nameplates is identical, but since I'm not sure if this confirms that they are using the same charger, I have uploaded the images of the nameplates.

The vacuum system should be airtight, but it seemed to whistle slightly near the N75 valve when I disconnected the hose while tracing it back to the vacuum pump. Then, I connected a new line directly from the T-connector (where the lines for both the N75 and the EGR valve split) to the vacuum actuator, bypassing the N75 completely, but there was no change.

I also had the old turbo disassembled; perhaps we can identify a problem based on its appearance. The VTG is easy to move; I even tested it while it was installed, and there were no obstructions or anything like that back then. I've read that excessive soot on the exhaust side can indicate a defect in the exhaust system, such as an overfilled DPF. Is that correct? The passenger side doesn't have one yet, but maybe something else is causing it 'there'. In my opinion, it seems quite sooty?!

Thank you and best regards.

Edit:

Perhaps it would be helpful if we set aside this particular Passat, including the new, potentially faulty turbocharger, and I introduce you to a second Passat with the same problem, as that might make things a bit easier?

This one has the first turbo, and as I determined from the second one, it is 99.9% fully functional. The VTG linkage does exactly what it's supposed to do, the compressor wheel has no radial or axial play, and there is no overshoot of the LD (like in a new one). Additionally, the mass airflow sensor (MAF) was already replaced because someone previously thought it should be producing around 1200mg/H (I will upload a log file - but as mentioned, it's been chipped for quite some time now), which of course achieved nothing. Now we have 3 MAFs, all of which should work, and one is just lying around. Also, the N75 valve was replaced; the old one was actually defective (about 4-5 years ago).

If there's nothing unusual to be found in the log here, can we assume that something is wrong with the exhaust system? Or are there other possibilities? As mentioned before, the noise was already audible *before* the tuning, but it was almost imperceptible; otherwise, we wouldn't have had it done. Over the years, it has simply become louder (and louder), gradually and not suddenly.

Thank you very much again.

It's somewhat naive to assume that you can identify all existing errors based solely on those two images.

"Make sure to address all the points that have been raised."