Intermittent Power Loss & Turbo Issues? Get Help!

Hello everyone:

"I occasionally experience a noticeable loss of power when running with reduced boost pressure, and I would appreciate any helpful comments."

Problem: Most of the time, the bus runs very well. However, under load, the boost pressure briefly rises to 1.2 bar and then quickly regulates back down to 0.9 bar within 1-2 seconds.

"Every now and then, roughly every fourth traffic light, I experience a noticeable loss of power. The turbocharger pressure doesn't exceed 0.6 bar until I reach engine speeds above 3,200 rpm. Then, the turbo pressure briefly spikes to well over 1.2 bar, and I have full power again, and everything is okay, until the problem repeats itself sometime later."

Vehicle: VW T3 Bus with 1Z TDI engine, chipped to 110 horsepower, with a new turbocharger, new magnetic valve, and a cleaned mass airflow sensor (Pierburg).


So far, I've tried:
1.) I thought the Westgate valve was stuck, so I replaced the Tubor, but it didn't make a difference.
2.) Replaced the LMM (mass airflow sensor), but it didn't make a difference.
3.) New solenoid valve, doesn't change anything.
4.) Error memory, empty.
5.) The hoses appear to be okay.

What should I check next?


Thank you very much.

Lukas.

Hi,
I'm guessing it's a faulty AGR valve that's not closing properly.

Greetings.
Reuselkopp.

Das AGR Ventil wurde mit dem Turbo getauscht, da es klemmte und dann dennoch mit einer Stahlplatte verschlossen. No AGR for me...

Any other suggestions?

Thank you.
Lukas.

I was never able to fix the problem until recently, when I replaced the nozzles.
Since then, the problem has been gone.
I'm guessing it's the needle valve actuator.
Do you think that's possible?

Regards,
Lukas.

I think that's unrelated. According to your description, the problem is called "overboost" and is registered as an error in the control unit as "pressure regulation difference exceeded." However, I've noticed that this isn't always the case. As a result, the control unit reduces the power output, which manifests similarly to your description. The cause of this is usually a stuck or difficult-to-move variable geometry turbocharger (VNT).
Best regards,

The 1Z engine does not have a VNT (Variable Nozzle Turbine).
Regards,
Lukas.

"Ugh, completely wrong. If it doesn't have a VNT (Variable Nozzle Turbine), then you might suspect a faulty wastegate or pressure sensor. You already replaced the ATL (Air Temperature Line), did you also replace the pressure sensor? We sometimes have problems with wastegates that get stuck in the socket. It's not noticeable when the engine is cold, but when it's warm, it can seize. Also, the eyes of the control rod often come loose due to corrosion. In both cases, the pressure gauge will then malfunction."
Best regards,