Experiences with seized VTG couplings, especially for AFN drivers

Hello everyone.

"On my '97 AFN, this problem occurs almost regularly (clearly visible on the boost gauge): after a strong acceleration and then quickly releasing the accelerator pedal (e.g., when shifting), there is often no more boost built up because the VTG apparently briefly goes into its resting position and "gets stuck" there. However, with gentle acceleration, there is always boost."

Even after a cold start, it sometimes takes a few minutes for the turbocharger to "de-clog" and for the boost pressure to build up normally (approximately 0.4 bar at 1,400 rpm).

The most noticeable symptom of sticking/sooty turbocharger variable geometry vanes is (besides the excessively low boost pressure reading – if present on board) a start that resembles an SDI engine rather than a TDI engine.
Occasionally, especially when accelerating rapidly from low RPMs, very high pressures (exceeding 1.5 bar) can be briefly observed on the display, but this has not yet caused the engine to go into limp mode in my case.

I suspect I'm a victim of the initially installed "small" turbocharger membrane canisters (diameter approximately the same as the pressure pipes between the turbocharger and engine), while newer versions have larger canisters (approximately the size of the thick pipes between the mass airflow sensor and the turbocharger), which can therefore generate more power.

I would be interested in hearing about the experiences of other VTG owners. To get a comprehensive overview, please provide the engine type and year of manufacture, as well as whether a small or large turbocharger was installed, along with any problems you may have encountered (or not).

Hi Ulf,

'After about 50,000 km, I experienced a stuck variable turbine geometry (VTG) on my car. However, the symptoms were different for me. I was already reaching maximum boost pressure at around 1400 rpm. There was a brief overboost of approximately 1.3 bar, followed by a regulation to a constant level of 1.1 bar.'

However, starting around 3600 rpm, my engine control unit went into limp mode due to excessive boost pressure because the variable turbine geometry (VTG) was stuck and could no longer open the exhaust flow.

I received a new one as a gesture of goodwill.

Currently, the total mileage is 82,000 km and there have been no problems... *knock on wood* three times!


I'm not sure if it was a large or small can of soda... sorry, I don't know!

Best regards from Lake Constance.


Audi A3.
Type 8L.
ASV
81 kW (97 kW with *** chip).
Price: €10.99

So, I also had that problem...

More frequent emergency braking (especially on uphill sections after sharp right-hand turns, but also occasionally on straight roads).
A certain sticking or binding would then often manifest as uneven acceleration.
I was able to prevent the emergency mode from being activated by adjusting the VTG linkage on the engine, but I haven't been able to eliminate the unpleasant acceleration.

(Volkswagen Golf III AFN, manufactured in September 1996)

Hello again,
I can only agree with Ulf. I've already mentioned this in the old forum before. My AFN, manufactured in 8/96, constantly had problems with the VTG (Variable Turbine Geometry). By replacing the turbocharger (same compressor, larger pressure sensor) and, unfortunately, the necessary engine control unit and control valve, it now runs perfectly for over 160,000 km without any issues. Especially since I've been driving about 200 km on the highway weekly for the past 2 months, the speedometer is almost at 215 again, and it runs very smoothly!

Docter wrote:

So, I also had that problem... it often went into limp mode (especially when going uphill after sharp right turns, but sometimes also on a straight road). A certain sticking or binding would then often manifest as uneven acceleration. I was able to prevent the emergency mode from being activated by adjusting the VTG linkage on the engine, but I haven't been able to eliminate the unpleasant acceleration. (Volkswagen Golf III AFN 9/96)

Hi Doc,

Did you also have a boost pressure gauge on board?
"In my opinion, the emergency mode should only occur with excessive boost pressure, but the result – a lack of power – is essentially the same as if there were no boost pressure at all."
So far, even short-term pressure drops to 1.5 bar have not caused a loss of power or limp mode in my vehicle.
So, how do you know that your car was actually in emergency mode?
Does the indicator light blink?

Even if the symptoms disappear after restarting the engine, it could be due to a VTG (Variable Turbine Geometry) blockage that was temporarily resolved by stopping and restarting the engine – so it's not necessarily conclusive evidence of a limp mode.

Okay:

Unfortunately, I didn't have a boost pressure gauge.

I still think it was an emergency landing because:

1. After restarting, it's almost back to normal.
2. Error entry: 'Intake manifold / control differential'.
3. I could imagine that the car might also go into emergency mode if it cannot achieve the required boost pressure.

It would also disappear after each immediate restart.
Unfortunately, an error is not indicated by the preheating lamp; I find this unacceptable, as it should display every error entry.

Hi Doctor.

Quote:

I still think it was a failsafe because: 1. Almost back to normal after restarting. 2. Error entry: "Intake manifold / control differential". "I could imagine that the car might also go into emergency mode if it cannot reach the required boost pressure." It would also disappear after an immediate restart every time. Unfortunately, an indication via the preheating lamp does not occur,

.

Sure, the conclusion seems reasonable given the observations.

"When accelerating strongly in 3rd gear from around 1300 rpm, I consistently see the intake manifold pressure reaching approximately 1.4 bar for about 1 second, but so far there have been no error messages related to intake manifold pressure control difference."
This is interesting because I often "manipulate" the VTG (Variable Turbine Geometry) using a rectangular wave generator connected to the solenoid valve (switchable out of normal operation during driving). In this case, the engine control unit has no control over the boost pressure anymore, and actual pressures between 0 and 1.2 bar can occur, whereas in normal operation, for example, it would be 0.6 bar.
So it seems that even relatively minor failures in the boost pressure regulation system must occur before an error message is generated.

I'm not so sure about the "vacuum" emergency mode explanation: with stubborn clamps stuck in the VTG (Variable Turbine Geometry) resting position, it takes almost 3000 rpm to build up only about 0.8 bar of pressure – that's pretty bad. I've experienced this myself, but still didn't get any error messages.

Maybe the pressure sensor is faulty.
Or could the EL/pneumatic transducer and all the resulting effects not be solely due to the VTG adjustment?

1.4 bar is quite a lot (in my opinion).

Unfortunately, I cannot provide any information related to boost pressure values... [/quote]

Hi Doctor.

Quote:

Maybe the pressure sensor is also malfunctioning? Oder gar der el/pneumatische Wandler und alle Effekte liegen gar nicht "nur" an der VTG Verstellung?

I've had those thoughts too.
Apart from the excessive pressure fluctuations and occasional lack of build-up, the pressure is otherwise regulated normally - which indicates that the sensor and EPW (which I have disassembled multiple times without finding any malfunctions or dirt accumulation) are functioning correctly.

On the other hand, the fact that the VTG (vehicle traction generator) regularly jams in the resting position and exhibits slight snagging in the upper area is a known issue, which, in my opinion, can explain all the observed problems.

Hi everyone,

nicht nur euch plagt dieses leidige Thema 'klemmende VTG'. Ich hatte schon mal im alten Forum über meine Probleme damit berichtet. Nach einem Tip von Ulf hab ich dann auch die VTG mal mit der Warnblinkanlage durchgeknetet. Danach konnte ich auch eine leichte Besserung verspüren(weniger Notlauf, wellenförmige Beschleunigung wurde weniger). Leider war nach 2 Wochen alles wieder beim Alten, d.h. wellenförmige Beschleunigung und Notlauf bei starkem Beschleunigen berghoch aber auch nach längerer Vollgasfahrt klemmen der VTG in Stellung max. Druckaufbau. Spätestens in den kommenden Semesterferien will ich dieser Sache ein Ende machen, denn ich hab es doch so langsam satt, immer auf das Manometer schauen zu müssen. De'When my VTG (vehicle registration document) gets stuck again, I...''The typical boost pressure is usually around 1.5 bar. Less frequently, when driving uphill and applying full throttle, pressures of up to 1.8 bar can occur. At these values, the TDI driver will naturally feel unwell just by looking at the boost gauge. Furthermore, I also experience this wavy acceleration pattern, which isn't surprising when you observe the pressure gauge during acceleration.'
My initial thought was to install the larger vacuum pump from the newer turbocharger, but I read a few posts earlier that it only works with a modified valve and a new control unit, which would obviously exceed the budget significantly.
Is that really true??? Why couldn't it just work with the large container?

Volkswagen Golf 3 GTI TDI '20 Years' Edition, manufactured in October 1996, with 128,000 km mileage and AFN engine.

Greetings from the North Sea.

Andy.

Hi,

Here's a possible translation:

"My suspicion is that using a larger vacuum chamber changes the behavior of the control loop, which consists of the boost pressure, the turbocharger, the solenoid valve, that very chamber, and the VTG adjustment."

This means that the control unit needs to send a different output signal to the solenoid valve depending on which pressure sensor is being used, in order to achieve the same effect.

Therefore, it would be worth checking (perhaps with Michaek II?) to see if there's a general rule that the control unit number also changes when the module is replaced in the series.

Or: Are there any production models with the large fuel tank at all, or is THAT the difference between AFN and ASV, which has also been searched for unsuccessfully in the past?

Best regards,

Jan.

Hi Jan,

Quote:

Here's a hypothesis: By using a larger vacuum chamber, the behavior of the control loop changes. This control loop is formed by the boost pressure, the turbocharger, the solenoid valve, that very chamber, and the VTG adjustment. Will heissen, dass das Steuergeraet bei einer anderen Druckdose anderen Output an das Magnetventil senden muss, um den gleichen Effekt zu erzielen.

Basically, you are right (for now).
Upon closer examination of the results in detail, however, it doesn't seem nearly as dramatic, in my opinion.
The solenoid valve has relatively small flow cross-sections. Therefore, it takes some time for the working pressure (which corresponds to the duty cycle of the valve control) commanded by the engine computer to actually "build up" inside the chamber.
With a larger container, the process naturally takes longer (which slows down the reaction), but on the other hand, the larger container builds up more force and can therefore overcome VTG clamps (or trigger them) sooner.
These two results from a larger container should at least partially offset each other, so my opinion is that a loader with a large container does not necessarily have to be completely incompatible with the software for the smaller container.

By the way, I emailed Volkswagen yesterday (May 3rd) about the conversion question and will share the results here.

Andy wrote:

Nach einem Tip von Ulf hab ich dann auch die VTG mal mit der Warnblinkanlage durchgeknetet. Danach konnte ich auch eine leichte Besserung verspüren(weniger Notlauf, wellenförmige Beschleunigung wurde weniger). Leider war nach 2 Wochen alles wieder beim Alten, d.h. wellenförmige Beschleunigung und Notlauf bei starkem Beschleunigen berghoch aber auch nach längerer Vollgasfahrt klemmen der VTG in Stellung max. Druckaufbau.

You're right, I've been experiencing something similar lately. Apparently, the kneading process can only remove a small portion of the stuck carbon deposits, which then tend to build up again quite quickly.

Even worse: it doesn't seem like my VTG (Variable Transmission Gear) is going to become fully operational again, even though I almost always have a control electronics unit for the valve on board and use it frequently.

Quote:

By the next semester break at the latest, I want to put an end to this problem, because I'm starting to get tired of having to constantly check the pressure gauge... Mein Gedanke war eigentlich die größere Unterdruckdose vom neueren Lader zu montieren, aber jetzt hab ich ein paar Beiträge vorher gelesen, dass das nur mit geändertem Ventil und neuem Steuergerät geht, was die Kosten natürlich bis weit über den Rahmen hinaus sprengen würde.

I am also still hoping for the simple method = just a larger container.
Did you have any other ideas in general?

Currently, I'm considering "spreading" the control output of the engine computer. It doesn't fully utilize the potential of this small component; for example, it doesn't apply maximum vacuum to the diaphragm even at idle, which is often insufficient to move the VTG (variable turbine geometry) from its stuck position.
If you pinch the hose between the air filter and the magnetic valve, the VTG (Variable Turbine Geometry) usually moves to its maximum position almost immediately. I achieve the same effect by applying the full vehicle voltage (instead of the signal from the engine control unit / switching via a relay) to the magnetic valve.
My thoughts are now turning towards a button that would allow users to manually mobilize the full dispensing power as needed, based on the same principle, or to control the process automatically via an idle contact.

That wouldn't solve the problems when the system is in its maximum position... Ultimately, you probably need an automatic system for continuous kneading even when idling, to keep the valve guide as clear as possible.

I will only start working on that once the larger size is deemed unfeasible.

I think the only solution for a stuck VTG (vehicle traction generator) is to remove it and verschandeln it thoroughly.

While the back-and-forth shaking might be a solution, it only gets truly verschandeln with manual cleaning.

So, you need to disassemble it, open it up (by heating the exhaust side with a torch), and verschandeln it. Then you'll have peace of mind for the next 100,000 kilometers.

Hi,

Okay, so if it turns out that using the larger container isn't feasible due to issues with the control system, then I will disassemble and verschandeln the turbocharger.
It seems that chemical methods are not effective for removing soot or carbon deposits, so only heating with a flame combined with mechanical cleaning of the parts will remain as options.
According to the previous owner, my car didn't exhibit these problems with the limp-home mode, which means the variable geometry turbocharger (VTG) worked properly for 120,000 km.
I assume that after a thorough cleaning, the gearbox will be able to run another 100,000 km without any problems.
I'm curious to see what solutions VW will offer in response to Ulf's request. But I think, as always, it will be nothing.

Greetings from the North Sea.

Andy.

Andy wrote:

My initial thought was to install the larger vacuum chamber from the newer turbocharger, but I read a few posts earlier that it only works with a modified valve and a new control unit, which would obviously exceed the budget significantly. Is that really the case??? Why couldn't it just work with the large can?

*excavation*
In my case, the MSG 012GH (G3 AFN) worked perfectly well with the large battery, and even simultaneously with a switchable auxiliary power supply: there were no abnormal voltage spikes or other issues.
Therefore, looking back, I can wholeheartedly recommend it – provided you can still find a large battery pack for the VNT15 these days...