Turbocharger ALH: Performance & Upgrade

Hello everyone,

"My wife's car, which has a G4 engine with an ALH turbocharger, has been experiencing a very noticeable turbo lag for some time. Below 1500 RPM, the accelerator pedal has almost no effect on torque; only above that does it slowly start to build power, reaching normal levels around 1800-2000 RPM."
The torque curve is incredibly smooth without any noticeable jerks or hesitations. The mass airflow sensor can also be ruled out because even with a diode emulator, the torque curve hardly changes at all.

When I compare the logged print quality data from my A3 with that of the G4, there's a huge difference between them.
I find it particularly striking that the turbo in the Golf, when the engine is cold and idling, still reaches approximately 20 mbar of overpressure compared to atmospheric pressure, while this pressure difference decreases with increasing oil temperature and eventually even becomes negative .
With a warm engine and a well-heated turbocharger, this thing actually acts as a flow restriction even at low load. I find that almost unbelievable, because the variable turbine geometry (VTG) is being controlled correctly. The turbocharger shaft also rotates normally and easily (at least when cold; I'd rather not touch it when it's hot).

In comparison, the turbocharger in my A3 provides approximately 20-30 millibars of overpressure at low load with a cold engine, which increases to around 80-100 millibars of overpressure as the temperature rises.

Is the charger for the Golf just scrap now?
I've also briefly checked the vacuum hoses to see if insufficient vacuum pressure might be the reason why the VTG isn't engaging fully, but I couldn't find any cracked or damaged hoses.

How about the N75? Could a defect in the pressure sensor affect such a slow build-up of boost pressure?

Thank you for your opinions.

Regards,
Alex.

My tip:
Try installing the AGR valve instead of the N75 (if possible), have the vacuum pressure checked, and perhaps try driving without the catalytic converter.

I think "Unterdruck" is a great tip; I've had the same experience. There was a porous hose directly connected to the pump.

Hello,

'Once, the connection nipple of my pressure accumulator (the black or green sphere on the cylinder head) broke, which caused pressure fluctuations in the system.'

The system pressure could not build up properly.

As a temporary fix (it was the weekend), I sealed the gap between the hose and the ball with hot glue. It worked great and it was immediately airtight.
The new ball had a piece of aluminum foil on one side; who knows what that's supposed to be for...

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

'MFG' stands for 'Mit freundlichen Grüßen,' which translates to 'Sincerely' or 'Best regards' in English. It is a common way to end a formal letter or email.

Brief update:

I put in the effort today and replaced all the vacuum hoses, unfortunately without success!

Therefore, only two candidates remain.

1. Turbocharger.
2. N75 pressure transducer.

The VTG system is working perfectly and can be completely ruled out as the cause of the problem.


Regards,
Alex.

Hello Donalexo,

The buckets on the loader itself are also undamaged, and the shaft rotates smoothly without excessive play?

donalexo wrote:

Brief update: I put in the effort today and replaced all the vacuum hoses, unfortunately without success! Therefore, only two candidates remain. 1. Turbocharger. 2. N75 pressure transducer. The VTG system is working perfectly and can be completely ruled out as the cause of the problem. Regards, Alex

Do you have enough vacuum pressure? Is the pump working properly? Are your brakes functioning normally?

donalexo wrote:

I find it particularly striking that the turbo in the Golf reaches approximately 20 mbar of overpressure 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 warm engine and a well-heated turbocharger, this component actually acts as a flow restriction even at low load. I find that almost unbelievable, because the variable turbine geometry (VTG) is being controlled correctly. The turbocharger shaft also rotates normally and easily (at least when cold; I'm hesitant to touch it when it's hot). In comparison, the turbocharger in my A3 provides approximately 20-30 mbar of overpressure at low load with a cold engine, which increases to about 80-100 mbar of overpressure as the temperature rises.

Hi Alex,

That's really strange.

If you were to post an online comparison of cold/warm MWB 11 logs for the ALH engine, specifically showing "full throttle from 1000 to 1500 rpm in 4th gear," it would be possible to analyze the control behavior.

"Initially, I can only imagine the following as potential causes:"
1. A heavily loaded and difficult-to-turn camshaft (if such a thing is even possible).
2. That the maximum vacuum at the VTG (vacuum transmitter gauge) is too low when it's warm (for whatever reason -> measure with a vacuum sensor or check the pneumatic system).
3. a VTG hot clamp that only allows the VTG to close about halfway.

Can you observe the VTG hub in the standard MWB 11 configuration (e.g., from a pit or by looking around a corner with a mirror) and compare its appearance when it's cold versus when it's warm?
For item 1, the hub should be the same size; for items 2 and 3, it should be smaller when viewed from a warmer angle.

Initially, I can only imagine the following as possible causes:
1. A heavily loaded and difficult-to-turn camshaft (if such a thing is even possible).


Hello everyone,

I believe this is possible if the oil supply becomes insufficient.

Aron once used the theme 'Turbocharger malfunction' for this topic.

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.


Interesting to note that...
I'm just speculating now:
According to the scenario where your oil supply is no longer optimal, the problem described above can be explained as follows:
When cold, the turbo is lubricated by the oil film and runs great. When hot, it can no longer dissipate heat effectively and expands accordingly. This makes it run more sluggishly.

Perhaps this could be a solution, as he also experienced a decrease in turbocharger performance with increasing engine (oil) temperature.

Best regards, Jochen.

Jochen_145 wrote:

I believe this is possible if the oil supply becomes insufficient: 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. According to the scenario where your oil supply is no longer optimal, the problem described above can be explained as follows: When cold, the turbocharger is lubricated by the oil film and runs great. When hot, it can no longer dissipate heat effectively and expands accordingly. This makes it run more sluggishly.

"Hmm, in that case, the oil flow through the loader would definitely have to be significantly reduced."

That would mean:
Disconnect the oil lines to and from the loader and check for a clear cross-section.
Check the oil flow through the charger (I once checked this on a disassembled charger using a syringe: surprisingly, 5W40 oil could be pushed through the charger quite quickly, not much slower than you would get through a cannula).
Check the oil pressure with a warm engine.