Boost Overboost on AFN After Turbo Replacement

Hi Experts ,
"I put my van out of service for the winter and took the opportunity to replace the turbocharger. The old turbocharger had the unpleasant habit of occasionally seizing up, meaning the adjustment of the guide vanes for boost control wasn't working. Repairing the turbocharger would certainly have been possible, but in my opinion, it wouldn't have been worth it, as the replacement turbocharger was only 100 euros more expensive."
"With the old turbocharger, the engine would always experience a temporary overboost of up to 1.2 bar for a few seconds when accelerating. Now, with the new turbocharger, the boost pressure stubbornly stays at 0.9 bar. Is this normal? I always thought that this brief overboost above the normal value was intentional in TDI engines. Am I mistaken? The old turbocharger also consistently maintained 0.9 bar under load, and nothing has changed in that regard."

Regards,
Jens.

Jens 16syncro wrote:

I always thought that this temporary increase in boost pressure above the nominal value was intended in the TDI engine. Was I wrong about that? The old turbocharger also always maintained the 0.9 bar as a constant value under load, and nothing has changed there.

Hi Jens,

I'm not entirely sure whether it's intentional or not, but the strength of the pendulum's swing can be adjusted using the VTG threaded rod.
When the swirl generators are removed, the pressure build-up, especially at low engine speeds, often becomes slower.

If you don't have any complaints about anything, just leave everything as it is.

Ulf: Isn't adjusting the lever very risky? It seems like the VTG (Variable Transmission Geometry) moves from its extreme positions to its extreme positions. If you shorten the lever to make it tighten faster, then it's possible (in my opinion, even likely) that the blades won't fully go to the minimum position when the lever is at one of its extremes.

I assume that a vacuum needs to be created inside the container first for the lever to move. So, if there's no pressure, the blades will be in the minimum position. Therefore, you need to screw the lever further in to make the loader engage faster, right?

Im unteren Drehzahlbereich beim erneuten Gasgeben nach einem Schaltvorgang (abbiegen etc.) haut er jetzt eine kleine Rußwolke raus. Das hat er vorher nicht gemacht, die Ursache muß also irgendwie mit dem neuen Turbo zusammenhängen. Es könnte also durchaus sein, das der Ladedruckaufbau zu träge ist, wie Ulf schrieb. Was kann ich genau machen, um das zu verbessern ? In welche Richtung müßte man denn das Gestänge verstellen ? Verkürzen wäre mir logisch, stimmt das ? Und wenYes, how much?

Regards,
Jens.

Hi,

Okay, you need to shorten the rod. It's hard to say exactly how much, but try starting with about half a turn.
Then it's better to ask for more if it's not enough.

Greetings.
Thomas.

kenny wrote:

Ulf: Isn't adjusting the lever very risky? It moves the VTG from stop to stop, I assume. If you shorten it so that it tightens faster, then it's possible (and in my opinion, even likely) that the blades won't fully go to the minimum position when the lever is at one of its stops.

Hi.
No: The charging mechanism has an adjustment range of approximately 1 cm, but the container has a significantly greater lifting range. However, this range is limited by the stops on the charging mechanism to a specific area, depending on the setting.
That means that even after (moderate) adjustment, both stops of the VTG are still reached.

Quote:

I assume that initially, a vacuum needs to be created inside the container for the lever to move, so if there's no pressure, the blades are in the minimum position. Therefore, you need to screw the lever further in for the loader to engage faster, right?

If you mean "to cut corners" --> correct.