Boost pressure problems on Audi A4 B5 1.9 TDi AFN 1996

Hi.
We're having a problem with my brother's Audi A4 B5 1.9 TDi AFN 110 hp, manufactured in 1996.

Error: No boost pressure, no power. After a short period of driving with the accelerator pedal fully depressed, the error message appears: "Intake manifold pressure regulation difference." However, the sensor indicated a maximum boost pressure of 1250 mbar, considering the atmospheric pressure of 950 mbar, which translates to a maximum boost pressure of approximately 0.3 bar.

Here's what we've covered:

1.) The turbocharger's pressure system has been depressurized. The hose at the turbocharger has been disconnected and sealed with a plug. The hose at the intake manifold has been disconnected and sealed with a plug that includes a pressure connection. If we put pressure on it (using a compressor through a tire inflator), nothing leaks out.

2.) VTG Adjustment: By applying vacuum directly to the vacuum chamber with a hand vacuum pump (thanks, Hans!), the adjustment rod moves upwards. The displacement is estimated to be 10-15 mm, depending on the vacuum level. It goes up and down smoothly.
Approximately how far is the driving distance?

3.) Vacuum system for control: Disconnect the hose from the BKV connector at the receiving end, connect a manual vacuum pump to the vacuum sensor, and pump it down. When evacuated, the vacuum should maintain a verschandeln pressure of -0.85 bar.

4.) Direct test of VTG adjustment: The first option involved testing without a vacuum hose connected to the control unit, and the second option involved connecting a hose directly from the pressure regulator (BKV) to the vacuum control unit (at -0.85 bar), bypassing any regulating valve. No changes were observed, whether the vacuum control unit was fully extended or fully retracted. It's important to note that we drove the car and repeatedly checked the error memory, and it also doesn't build any boost pressure until it's already in limp mode!

5.) Checking the boost pressure sensor: We disconnected the hose from the boost pipe that leads to the pressure sensor in the control unit. We attached a T-piece, a pressure gauge, and a tire inflator. The pressure gauge shows exactly the same reading as the MSG (presumably a diagnostic tool) measures. Also, the system is complete; when we have 1 bar of overpressure in the hose, it is maintained. The boost pressure sensor is doing its job excellently.

6.) Intake system up to the turbocharger: Everything is disassembled, there are no obstructions in the intake, and everything is clear up to the turbocharger.

7.) Turbocharger: The turbine shaft rotates freely, there is no slippage, and there is no significant play.

The exhaust system still needs to be checked, the mass airflow sensor needs to be replaced with a diode, and the turbocharger itself needs to be replaced.
We will then take a short drive tomorrow without the catalytic converter, and replace the mass airflow sensor (MAF) with a diode, so that the turbocharger directly vents to the atmosphere and the engine control unit (ECU) calculates the maximum airflow. Okay, then there's nothing else to do, the turbocharger needs to be removed, and the gas turbine needs to be lowered.

It all happened suddenly, with no gradual decline in performance. "Previously, there was occasionally an error message "Intake manifold pressure control difference" when accelerating with full throttle. This was typical behavior for a slightly sticking variable geometry turbocharger (VTG), meaning it only occurred when accelerating from a standstill with full throttle; if you accelerated more slowly, there was no problem."

Are there any other potential issues that can occur in the charging area? For example, ... Is the VTG adjustment mechanism internally damaged? Is the adjustment vane for the variable geometry ring broken or something similar?

Greetings.

Hello,

2) is okay.

Does the AGR valve remain stuck in the closed position under load?

Quote:

For example, the VTG adjustment mechanism might be internally broken, the adjustment blade for the adjustment ring might be broken, or something similar.

It's possible, but I've never experienced it.

It might be worth checking if the exhaust system is completely clear (e.g., catalytic converter rotated), because without a pressure difference at the turbine, there will be no boost pressure buildup.

Best regards, Rainer.

Hi.

The AGR gasket that is installed does not have a hole in the middle.

A faulty EGR valve with excessive exhaust gas recirculation can be ruled out. A 2 mm stainless steel plate placed at the intake manifold connection prevents unwanted entry of exhaust gases into the fresh air side.

Greetings.

Hi.
After the loader was removed and a replacement loader with an 80-ton capacity was brought in, it quickly became clear:

He can't be the one .

Nothing is broken, all guide vanes are rotating smoothly, all diverter levers are rotating smoothly, the ring is in good condition, and the through-shaft from the outside to the inside is in good condition. Okay, let's put it back together and start again.

It's working again .

Then I replaced the timing belt and performed other maintenance services for 180,000 km, and everything was fine for a week, covering about 1000 km without any problems.

Last weekend, I received the call: The performance was down again.

So, yesterday evening we did another dyno test, and it seems the only possibility is that something is still stuck in the intake system or the exhaust system. Okay, so I disconnected the catalytic converter and cleared the error codes, and suddenly the power was back.
Cat stuck briefly with a mother near the loader, again no power, and then emergency mode.

It was too late for any further repairs, so last night I quickly went to the rental workshop. I removed the catalytic converter and the intermediate pipe and shook them briefly. *Clink* *Clunk* *Clink*. Something's wrong...

Looking inside, one could see the remnants of the catalyst support, which had detached and, due to vibrations during operation, had taken on the shape of a large lump of coal. This perfectly sealed (truly airtight, with no light visible) within the conical outlet of the catalyst housing. The "egg coal" must have become dislodged from its confining position during the loading process (as it's quite loose in the exhaust pipe) and likely found its way back into the exhaust outlet a week later while braking downhill.

Several forceful strikes with my chastity device extension rod into the depths of the cat's enclosure revealed various dust and small debris, as well as some large pieces of charcoal briquette .

Everything back in place, out of the rental workshop, and finally able to enjoy the 110 horsepower again without restrictions. Now, all that's needed is a new cat .

I'll have the pictures for you tonight, but unfortunately, Carmen has my card reader with her.

Best regards, Matze.

P.S.: There's now a loader available that's in almost new condition, salvaged from a machine with 80,000 kilometers on the clock.

Thank you for the detailed explanation .

Hi.

I think you can pretty much imagine how this "potato," while still in one piece, had an exhaust pipe grafted onto its opening.

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Best regards, Matze.http://img502.

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