Golf IV ALH Turbo Failure Under Load

Hello everyone,

'When I drive my Golf IV 1.9 TDI, ALH, 66 kW, manufactured in August 2000, at full throttle on the highway, I think the turbo intermittently cuts out around 160 km/h.'
'I can barely reach 160 km/h; the car always briefly accelerates (for about 3 seconds) and then immediately loses power, and this happens repeatedly.'

It's always like that, not just occasionally!

I have checked the vacuum hoses, replaced the magnetic return valve, and the VTG (Variable Turbine Geometry) is operating smoothly.

Can anyone help me with this?

See you later...
mima

Hello mima,

What do the LMM values indicate? It sounds very much like that to me.
Otherwise, we have a large number of threads here with the same error message for self-study.

mima wrote:

When I drive my Golf IV 1.9 TDI, ALH, 66 kW, manufactured in 08/2000, at full throttle on the highway, I think the turbo sometimes cuts out around 160 km/h. I can barely reach 160 km/h; the car always briefly accelerates (for about 3 seconds), but then immediately slows down again, and this happens repeatedly.

Hi,

another case where LDA would be helpful

I suspect that the turbocharger pressure is getting too high.
Since the vehicle doesn't seem to be going into emergency mode, I suspect it's due to normal oscillations.

They could, for example, originate from a VTG (variable throttle governor) that is difficult to move in the "lower" range, i.e., a position close to the "engine off" position.
It's possible that the VTG (vaneless turbine geometry) is sticking due to excessively high exhaust gas temperature (EGT), which may be a result of the tuning. This might not be noticeable yet because the intercooler is still relatively cold.

Can you disable the tuning and let me take a test drive with the standard performance?

I replaced the LMM myself three weeks ago. However, I didn't observe any symptoms like that. My TDI just wasn't pulling well anymore, especially at lower speeds, below 120 km/h. The maximum speed was still 190 km/h, as usual. It just took a very long time to reach 190 km/h, and the car didn't make any of its usual noises, not even when I suddenly floored it.

I'm leaning more towards a fuel supply issue or a difficult-to-move VTG (Variable Transmission Gear).
However, in that case, the pauses between full power and no power would be significantly shorter than 3 seconds, as in your situation.

Wann wurde der Kraftstofffilter getauscht? Gibt es Luftbläschen im Schlauch zw. Filters and ESP?
Does this problem occur when the tank is empty as well as when it's full?

Why are you so sure about that?

I've already had mass airflow sensors that were defective right out of the box. Furthermore, I had exactly the same error symptoms with my 1999 G4 ALH. Let's wait for the diagnostic readings and then see what happens.
Anything else would be pure guesswork.

EDIT: Your AHU engine likely has a Pierburg mass airflow sensor, while the ALH engine has a Bosch mass airflow sensor.

Please provide the text you would like me to translate from German to English.
In your AHU engine, there is likely a Pierburg mass airflow sensor (MAF), and in the ALH engine, there is a Bosch MAF.

No, not necessarily...
michaelII once posted that, for example, the 'Boschige' material is also used in the 'ahu' (likely referring to a specific part or component).

There are AHUs with both versions, and also AFNs with both!!

These engines were manufactured during the transition period from Pierburg to Bosch.

There are, for example, AFN models with engine control units (ECUs) starting with 028 xxx yyy, and others with 038 xxx yyy.

Perhaps that was the key transition point, because the Bosch mass airflow sensor has a different connector, which means a different wiring harness is also required.

Here's the Pierburg part on my 1Z.

Yes, I have a Pierburg mass airflow sensor installed (and that's a good thing!).

However, this has nothing to do with the problem described above!
If a defect is already present when the product leaves the factory, such as with the new LMM, then it's a different situation. It simply varies how the control system reacts to that defect.
For me, it was a 'dated' mass airflow sensor, considering it had 126,000 km on it. No Bosch mass airflow sensor can compete with that!

For further discussion, we need to wait for more measurements from mima.

Thank you for the photo Martin.

That's exactly the one I have in my AHU.

Hello,

Meanwhile, I can also imagine that the mass airflow sensor (MAF) is the cause, even if the boost pressure fluctuates.

I'm starting a new thread because it concerns a fundamental issue with TDI.

Hi,

I've experienced something similar before. In my case, the cause was a clogged diesel filter. At certain speeds (engine RPMs), the vacuum was so strong that it was drawing in air. However, this only lasted for a few days, after which the filter became so clogged that the engine could barely run.

Greetings.

Eike.

Hello again, and thank you for the answers.

After several attempts, I managed to solve the problem differently. I replaced my Bosch mass airflow sensor the day before yesterday, and the problem is now fixed.

No more jolts during acceleration, and no more sudden impulses when driving at full speed on the highway.
Previously, the car had trouble reaching 170 km/h, but now reaching 200 km/h uphill is effortless. It's a night-and-day difference.
It feels like I have a brand new car!

See you later...
mima

mima wrote:

The day before yesterday, I replaced my Bosch MAF sensor, and the problem is fixed.

Thank you for the "resolution" .

Hi mima, were you able to log any measurements?
That might be interesting to support Ulf's argument.

EDIT: Perhaps the faulty mass airflow sensor still exists? Ulf's Ibiza might have the same model installed, which would allow the problem to be reproduced.

Hi,

I'm sorry, I didn't have a way to log the values.
I returned the defective mass airflow sensor because a replacement part would be too expensive.

See you later...
mima

P.S. The man with the new car !