VTG Failure: Troubleshooting Loose Coupling Issues

Hello fellow enthusiasts,

I have a problem with my Superb, specifically the turbocharger with engine code BSS.

I already had...
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I described my struggles with LD overboosters and a brutal correction method. The question is whether the chip tuning is the problem, or if my VTG (Variable Turbine Geometry) turbocharger is actually broken.

The initial state is: The engine has been chip-tuned to 160 horsepower / 360 Nm, the N75 valve is new, the vacuum hoses have been replaced, and a calibrated pressure gauge shows brief (<1 second) pressure spikes between 1.6 and 1.9 bar when abruptly accelerating from 2500 rpm. The target boost pressure at that RPM under full load is 1.5 bar.

Da denkt doch jeder: VTG. Me too .
Okay, I unscrewed the pressure vessel and checked the adjustment range.
Result: Very soft. Estimated adjustment force < 1 N.
Adjustable range: approximately 11 mm.
Spritzentest: Sieht super aus. Can sealed.

So, maybe it is faulty software after all? But having them investigate and potentially revert to an older version costs 350 euros. I can get a new (genuine) turbocharger for 450 euros.
Where is the best place to invest money?

Well, to narrow down the issue further, I'd like to ask if you've ever experienced a situation where a VTG adjustment was defective, even though it felt very smooth and worked perfectly in the injection test ?

Best regards, Georg.


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Have you ever measured negative pressure?

Hängt die Dose auch nicht und ist komplett dicht, eventl. Broken feather?

While this is the "basic" version, why are you buying a used engine control unit (ECU) on eBay or somewhere else? The part number is 03g906016gt. Alternatively, I can check if I have anything suitable available, load the correct software onto it, and remove the immobilizer, so you could test it temporarily as a plug-and-play solution.

Georg_G wrote:

Well, to narrow things down further, I'd like to ask if you've ever experienced a situation where a VTG adjustment was defective, even though it felt very smooth and moved perfectly during the injection test ?

Short and concise... YES!!

/viewtopic.php?t=8591&highlight=vtg+verklebt&start=10

"Defekt" isn't quite the right word here...

Thank you for the answers so far.

Bertil, thanks for the heads-up about the sticky VTG.
I had considered it before, but then dismissed the idea because the injection test looks good.

I just got a new turbocharger from a VW prototype engine (never used). I'll be installing it next week and will let you know how it goes.

Best regards, Georg.

Hi.

Instead of replacing the turbocharger, I could have simply disassembled and cleaned it. When disassembled, you can see scratches or burrs where the variable geometry (VTG) components might be stuck. So far, I've been able to fix every turbocharger this way, unless the shafts were worn out or broken.

@"wingmaster"
The VTG (vertical travel gauge) doesn't stick and has a full range of adjustment.
The problem seems to be more likely related to the membrane module. While it could be replaced individually, if one could obtain the replacement part...

@"TDI-GTI-4-Motion"
I measured the vacuum pressure at the inlet to the N75 using an uncalibrated pressure gauge (with an accuracy of approximately +/- 0.1 bar). The absolute pressure there is about 50 mbar, which is consistent with other functioning TDIs.

Okay, so now we're going to replace the turbocharger, and hopefully that will put an end to all the speculation .

Best regards, Georg.

Georg_G wrote:

I measured the vacuum at the inlet to the N75 using an uncalibrated pressure gauge (with an accuracy of up to +/- 0.1 bar). The absolute pressure there is approximately 50 mbar, which is consistent with other functioning TDIs.

Yes, that seems correct.

Feedback:

I've now installed a new turbo. With this one, the overboost is within the normal range: approximately 0.1 bar during acceleration from low RPM.

Interestingly, the VTG adjustment felt the same on both the new and old turbochargers, and exhibited almost identical behavior when actuated by vacuum drawn with a syringe. The old turbocharger showed a slightly slower reaction time, but only if you could hear the fleas coughing .

This minimal difference in the VTG (Variable Transmission Gear) engagement, likely caused by an aged pressure canister, resulted in my over- and underswinging.

This observation sheds new light on the injector test and the VTG inspection, which involves carefully examining and feeling the components. Even the smallest deviations from the original smoothness of all components can have a significant impact under unfavorable conditions, which in my case includes the chip tuning I have installed. However, such a slight difference in the VTG's smoothness may be impossible to detect and assess when the component is installed.

Thank you all again.
Best regards, Georg.