Turboloch ALH

Hello everyone,

The ALH in my wife's G4 has been experiencing a very pronounced turbo lag for some time, meaning that below 1500 1/min, the accelerator pedal position has almost no effect on the torque. Only after that does the boost gradually build up, reaching normal levels around 1800-2000 1/min.
The VTG moves incredibly smoothly without any sticking or hesitation. The LMM is also to be excluded because even with diode simulation, the torque profile changes very little.

When I compare the logged pressure curves of my A3 with those of the G4, there's a huge difference.
What I find particularly striking is that the turbo in the Golf achieves an overpressure of approximately 20 mbar compared to atmospheric pressure when the engine is cold and idling, while this pressure difference decreases with increasing oil temperature and eventually even becomes negative .
With a hot engine and a well-heated loader, this creates a flow restriction even in the low-load range. I find this almost unbelievable, because the VTG is being correctly controlled. The crank shaft rotates smoothly (at least when cold; I'd rather not touch it when it's hot).

In comparison, the charger in my A3 provides approximately 20-30 mbar of overpressure in the LL with a cold engine, which increases to approximately 80-100 mbar of overpressure as the temperature rises.

Is the charging system in the Golf just scrap now???
I have also briefly checked the vacuum hoses, just in case the low vacuum pressure was the reason why the VTG wasn't operating at maximum speed, but I couldn't find any damaged hoses.

How about the N75? Could a defect in the pressure converter affect the slow build-up of the charging pressure in this way?

Thank you for your opinions.

Greetings
Alex

[Translating...]

Mein Tipp:
AGR-Ventil mal anstelle N75 montieren (falls möglich), Unterdruck mal messen (lassen) und vielleicht mal ohne Kat fahren.

Unterdruck finde ich ein heiße Tipp, hat sich bei mir auch genauso geäußert... Direkt an der Pumpe war ein poröse Schlauch.

[Translating...]Hallo,

bei mir war mal der Anschlußnippel des Druckspeichers (schwarze bzw grüne Kugel am Zylinderkopf) gerissen, hat dann für Druckschwankungen im System gesorgt.

Der Systemdruck konnte sich nicht richtig aufbauen.

Als Nothilfe (war Wochenende)hab ich den Spalt zwischen Schlauch und Kugel mit Heißkleber gedichtet. Hat super funktioniert und war sofort dicht.
Die neue Kugel hatte dann eine Alufolie auf einer Seite, wer weiß wofür das gut sein soll...

MFG

[Translating...]

Kurzer Zwischenstand:

Ich habe mir heute die Mühe gemacht und alle Unterdruckschläuche ersetzt, leider ohne Erfolg!

Somit bleiben nur noch zwei Kandidaten übrig:

1. Turbolader
2. N75 Druckwandler

Die VTG funzt butterweich, kann absolut ausgeschlossen werden.


Gruß
Alex

[Translating...]Hi Donalexo,

die Schaufeln am Lader selbst sind auch noch unversehrt und die Welle dreht noch ohne zu großes Spiel?

[Translating...]

donalexo wrote:

Kurzer Zwischenstand: Ich habe mir heute die Mühe gemacht und alle Unterdruckschläuche ersetzt, leider ohne Erfolg! Somit bleiben nur noch zwei Kandidaten übrig: 1. Turbolader 2. N75 Druckwandler Die VTG funzt butterweich, kann absolut ausgeschlossen werden. Gruß Alex

Hast du denn genug Unterdruck? Ist die Pumpe o.k.? Funzen deine Bremsen normal?

donalexo wrote:

What I find particularly striking is that the turbo in the Golf achieves an overpressure of approximately 20 mbar compared to atmospheric pressure when idling with a cold engine, while this pressure difference decreases with increasing oil temperature and eventually even becomes negative. With a hot engine and a well-heated loader, this creates a flow restriction even in the low-load range. I find this almost unbelievable, because the VTG is being correctly controlled. The crank shaft rotates smoothly (at least when cold; I'd rather not touch it when it's hot). In comparison, the compressor in my A3 provides approximately 20-30 mbar of overpressure in the LL with a cold engine, which increases to approximately 80-100 mbar of overpressure as the temperature rises.

Hi Alex,

That's really strange.

If you ever want to compare the MWB 11 log data, cold/warm, of the ALH "Full throttle from 1000 to 1500 rpm in 4th gear, "If you upload a "Gang" online, you could analyze their behavior.

Initially, I can only imagine the causes as potential factors.
1. a single, very heavy and difficult-to-operate loading shaft (if such a thing is even possible)
2. that the maximum negative pressure at the VTG is too low when warm (regardless of the reason -> measure with suction-LDA) Pneumatic system check
3. a VTG-clamp that allows the VTG to only close ~ half.

Can I observe the VTG hub in the MWB 11 basic settings somehow (e.g., on a pit, or by looking around the corner with a mirror) and compare it to cold and warm?
At 1, the lift should be the same. At 2 and 3, it should be warmer and smaller.

In advance, I can only imagine the possible causes.
1. a single, very heavy and difficult-to-operate loading shaft (if such a thing is even possible)


Hello everyone,

I believe this is possible if the oil supply is no longer sufficient:

Aron had once discussed this topic under the heading 'Turbocharger Sticking':

/viewtopic.php?t=15333


Interesting about this
Let me speculate:
According to the scenario where your oil supply is no longer optimal, the above-mentioned problem can be explained:
In the cold state, the turbocharger is lubricated by the oil film and runs perfectly. In the warm state, it can no longer dissipate the heat effectively and expands accordingly. Hereby, it becomes more difficult.

Perhaps this could be a solution, as his charging performance also decreased with increasing engine (oil) temperature.

Best regards,
Jochen

Jochen_145 wrote:

I believe this is possible if the oil supply is no longer sufficient: /viewtopic.php?t=15333 According to the scenario where your oil supply is no longer optimal, the above-mentioned problem can be explained: In the cold state, the turbocharger is lubricated by the oil film and runs perfectly. In the warm state, it can no longer dissipate the heat effectively and expands accordingly. Hereby, it becomes more difficult.

Hmtja, for this, the oil flow through the charger would definitely have to be significantly restricted.

That would mean:
Remove and inspect the fuel line from and to the charger
Check the oil flow through the pump (I once checked this by removing the pump and using a syringe: I was able to get 5W40 oil through the pump very quickly, not much slower than if I had just gotten it through the cannula opening)
Check the oil pressure when the engine is warm.