Boost Pressure Drop: AFN Help & Troubleshooting

Hi,

My father is having a problem with the turbo boost on his AFN vehicle.

Here's the translation:

"To begin with, my father is currently in Morocco and therefore has to largely rely on himself. He has already tried to find and locate the problem himself, but he hasn't been successful so far. That's why he asked me to describe the problem to you, hoping that one of you might be able to help him."

Okay, here's the translation:

"Now, regarding the problem: After the engine starts and my father drives off, the turbocharger pressure only builds up to 0.8 bar (normally it's 1 bar). With this boost pressure, he can drive until the engine warms up, but then the boost pressure drops to 0.3 bar, and the performance noticeably decreases."
Since my father has a laptop with him, he was able to read the error codes, and it only shows "intake manifold pressure control difference."
He also performed an actuator diagnosis, which revealed no malfunctions. He replaced the mass airflow sensor, checked the variable turbine geometry (VTG), replaced the boost pressure control valve, and inspected all hoses. Replacing the parts did not change the problem, and all the components that were checked are functioning correctly.

He hasn't yet checked whether the control unit that interfaces with the VTG is fully functional, and whether the EGR valve is stuck.
(The exhaust gas recirculation valve is functioning correctly.)

Now the question is: if the EGR valve is activated but gets stuck, could it be that the turbocharger can no longer build up pressure?

It would be great if I could get some quick help, as my father would really like to continue his vacation without any interruptions.

"Thank you!"


Moritz.

harix84 wrote:

Now the question is, if the exhaust gas recirculation valve is activated but gets stuck, could it be that the turbocharger can no longer build up pressure?

Probably not, because the relatively unrestricted flow from the intake manifold to the exhaust manifold should still allow the turbocharger to function reasonably well.

On the VW Golf 3 AFN, there's a thin hose running from the intake manifold to the engine control unit (which houses the boost pressure sensor) – it's located in the coolant reservoir area.
If the hose detaches or develops a leak, it can lead to symptoms like these.

Thank you, Ulf, for your explanation.

The problem has now also been located elsewhere. When checking the valve that controls the VTG (Variable Turbine Geometry), it was found that the valve is leaking, which prevents the VTG from being properly controlled. It is likely that the hole in the valve expands with heat, which explains why the boost pressure drops when the engine is warm.
Now we just need to find one more can; usually, they only come with the complete turbocharger kit. But let's see, I'm sure we can figure something out.

Moritz.