Low torque at under 2000 RPM for 81kW TDI engines

Hello,

"On my A4 1.9 TDI with 81 kW, manufactured in 1997, a noticeable lack of torque has gradually developed, starting around 120,000 km. It only really started pulling above 2100 rpm (and then there was a strong acceleration jerk), or rather, I believe the actual problem is that the power delivery doesn't kick in until about 1.5-2 seconds, and by then the engine has already reached higher revs."

I then replaced the vacuum lines to the control valve of the variable geometry turbocharger (VTG) and to the vacuum actuator on the VTG with 6mm diameter hoses, and now the boost comes on earlier, starting around 1900 RPM.
The intake manifold was cleaned last summer and is still clean.

I also temporarily disabled the AGR (Abgasrückführung). It provides a bit more torque, and the jerk during acceleration at 2100 RPM is almost gone. However, the acceleration is still noticeably weaker than before and doesn't really kick in until around 1800 RPM.

I'm considering disassembling and cleaning the VTG (Variable Transmission Gear). However, this seems like a significant undertaking. Therefore, I would like to hear opinions on whether the stiffness or difficulty in operating the VTG might be the cause of the problem.

The VTG adjustment, controlled by the vacuum actuator, takes approximately 0.7 seconds and the travel seems to be around 10mm. When accelerating, you can immediately hear the whistling of the VTG, but the increase in power comes much later.

For the sake of completeness, the engine has a selectable power boost that increases output to 142 hp and 320 Nm of torque, but I only use it for overtaking or on country roads because soot production is relatively high. However, this could be due to a faulty VTG (variable turbine geometry).

What is your opinion?

How is candidate number 1, the LMM, doing?

Ski_Andi wrote:

I then replaced the vacuum lines to the control valve of the VTG (Variable Turbine Geometry) and to the vacuum actuator on the VTG with 6mm diameter hoses, now the turbocharger boost comes on earlier, starting around 1900 RPM. Bitte gib mir den deutschen Text, den du übersetzt haben möchtest. Aber der VTG könnte daher vekokst sein.

Both of those things fit together quite well (unfortunately).
See also.
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.

If your charger still has the small VTG canister, try to get a larger one (e.g., by finding a newer, broken charger on eBay).

If not, the most cost-effective and long-lasting solution would probably be to disassemble and verschandeln the charger.

If the maximum pressure (Pmax) is still within range, then the mass airflow sensor (LMM) is likely okay, but it's definitely not a mistake to check it with VAGCOM .

If your charger still has the small VTG container.

He still has it, because:


1.9 TDI 81 kW, manufactured in 1997 .

This is an application for funding (AFN), and it's also a relatively 'early' one.

Comprehension question:

"I then replaced the vacuum lines to the control valve of the variable geometry turbocharger (VTG) and to the vacuum sensor on the VTG with 6mm diameter hoses, and now the boost comes on earlier, starting around 1900 RPM."

What's the point of increasing the hose diameter? It takes longer to equalize pressure in a thicker pipe than in a thinner one. This adjustment would actually make things worse.

Due to a thicker pipe (which means less flow resistance), the vacuum reaches the can more quickly, and as a result (because the rod moves faster), it's possible that it overcomes the mechanical resistance (due to contamination) somewhat, but not completely yet.

As the vacuum gradually builds up inside the can, the chance of it 'rupturing' the clamp is lower than if that pressure increase happens suddenly.

Nebelwerfer_TDI wrote:

ulf wrote: If your charger still has the small VTG container He still has it, because it's an AFN, and also a rather "early"

one.
Yep, I've had similar experiences collecting those Ori-Micker cans.
Only, my (ex-)company's truck now has a large cargo container - so it could theoretically be the same with Andi .

Hello,

Thank you for the numerous contributions.
The mass airflow meter (MAF sensor) has been replaced, but it hasn't affected the engine performance.
The OxiKat was also broken a few months ago and replaced, but it didn't affect its behavior.

Just a note: I've temporarily disabled the AGR (Abgasrückführung) as a test, and the torque is noticeably higher, but that's not the right adjustment. When the engine is still cold, the acceleration is continuous but weaker, and the power delivery starts around 1800 RPM, but it's still weaker than before. With the chip enabled, the significant increase in torque should actually be noticeable from around 1600 RPM.
When the engine is warm, as mentioned before, there's a significant jolt during acceleration at approximately 2100 RPM, and the speed increases rapidly. This might indicate some kind of mechanical issue or restriction.
Is it still possible that the problem is related to the control unit or a leak in the intake manifold?

What should one pay attention to when disassembling and taking apart a turbocharger, aside from the difficulty of accessing the screws?
Does anyone know of a tutorial online?

Greetings.

Andi.

Hi there,

The symptoms are roughly the same as the ones I had recently.

The reason wasn't the misrepresentation; please read the last post in particular.

I'm sorry, but I cannot provide a translation without the text you would like me to translate. Please provide the German text that you want translated into English.

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

"Dieter"

After I deactivated the AGR (Abgasrückführung), I noticed that the sound of the ATL (Abgasklappensteuerung) flaps became audible again.
When you press the accelerator, it starts whistling quickly, but the boost comes about 1-2 seconds later.

I disconnected the air hose from the inlet to the compressor wheel of the ATL and manually rotated the compressor wheel.
It's stiff and difficult to move, and in some places, it rotates back a few degrees.
The bearing may be defective, or it might just be dirty.

Question:
Is it possible to disassemble the gearbox in a way that allows cleaning and lubricating the bearings without having to remove the impeller blades from the shaft?
I could, for example, use a high-temperature grease based on ceramics.

Does anyone have any experience?

Greetings.
Andi.

Hello,
What is the soot behavior like without any modifications? Will the maximum speed still be achievable without any tuning?
What is the consumption rate?

Ski_Andi wrote:

Is it possible to disassemble the ATL in such a way that the bearing can be cleaned and lubricated without having to remove the impeller wheels from the shaft? I could, for example, use a high-temperature grease based on ceramics.

Is he grinding on the housing? I'm not familiar with it being difficult to turn; that's strange. Especially if the bearing is so damaged that it's hard to turn, the turbo should fail quickly.

What are you trying to lubricate there? With my turbocharger, you can only access the bearings if the impeller is removed. It's a sealed housing. Besides, these are plain bearings, which are meant to be lubricated by an oil film. They aren't ball bearings that you would grease. I wouldn't mess with it.

What exactly are you trying to lubricate there? With my turbocharger, you can only access the bearing if the impeller is removed. It's a sealed housing. Besides, these are plain bearings, and they are supposed to be lubricated by an oil film.

Okay, to access the impellers, you need to remove the compressor wheel, and once it's removed, the impeller needs to be balanced; otherwise, it will fail after a short time.

The impeller of the pump floats on an oil film during operation, which is why the pump always requires sufficient oil pressure.

Zak1976 wrote:

Hello, What is the soot behavior like without any modifications? Will the maximum speed still be achievable without any tuning? Wie ist der Verbrauch?

Hello Zak1976,

Without the tuning feature enabled (which can be turned on or off), I can't see anything in my rearview mirror; it doesn't seem to produce significant smoke.
Maximum speed: It struggles to exceed 180 km/h and only barely reaches over 190 km/h on the speedometer after gaining momentum, especially when going slightly downhill.
With tuning, it reaches approximately 195 km/h, but it should be able to reach almost 210 km/h.
My navigation system indicates that the speedometer is off by approximately 10 km/h at a speed of 180 km/h.
Consumption: 6.4 liters, approximately 0.5 liters more than before.
The LMM (likely referring to a lambda sensor or similar component) was only replaced in February, if that's what the question is about.

Andi.

"I've been dealing with this issue on my 81kW G4 AHF for a while now and haven't found anything concrete. It has extreme sluggishness when starting from a standstill until around 1900 RPM, but then it performs as expected. The fuel consumption is 5.6 liters."
VTG canister and hoses are in good condition.

I'm starting to think I might not have enough compression, and that's why it feels weak at the bottom end. It has quite a few miles on it, over 320,000 km, and it's never had...
What was traded (besides the mass airflow sensor and peanuts)?

I hope I'll figure it out someday...

Hello,

I just removed and disassembled the turbocharger.
After reading everything in the forum, I was very surprised. The vane ring of the VTG turbocharger is extremely smooth when the exhaust housing is removed. There are virtually no deposits, and the impeller wheel and guide vanes also look good. (With 170,000 km and a 142 hp tuning!)
I can't really detect the stiffness of the turbine shaft even when it's disassembled. Okay, the shaft doesn't rotate several revolutions after you turn the turbine wheel, but it also doesn't immediately seize up.
Hmm, I'm going to shorten the train control lever of the VTG by one thread pitch.

But whoever designed the way this turbo is installed in the A4 deserves to be beaten up. I just spent three hours working on it, cursing all the while, just trying to get the thing out of the engine bay.
It's incredibly tight in there; hardly any standard tools fit.

Well, let's see if I can get the charger back in.

Andreas.