T5 Emergency: 2.5 BPC Mode Activated (28-02-2016, 17:51)

Hello, I'm currently searching for something.
Boost pressure limit exceeded, emergency mode.
Often cold, good; hot, almost always.
Approximately 150,000 km, manufactured in 2006.
The boost pressure and air mass remain significantly below the target values.
Completed:
- Pressurize the low-pressure system with hoses to 1.5 bar for 1 minute.
- The vacuum pressure is 0.9 bar.
- Vacuum hoses to the turbo are fully connected and the turbocharger housing moves freely, with the VTG rod hitting its limit. It responds easily to pressure changes (when cold, there is no noticeable clicking or binding when moved by hand).
- Pneumatic valves replaced on VTG (Variable Transmission Gear) and AGR (Agile Ride Geometry) shift levers. Preheating system likely unnecessary.

What's noticeable to me is the 100% accelerator pedal travel ratio, which sometimes doesn't change with the accelerator pedal position, but remains at 100%!
Question: Does this indicate a willingness from the control unit (STGT) to change, or is the electric EGR valve actually always stuck in a 100% closed position? (Control unit to EGR: Please close/open the EGR valve).
The LOG error scans have been completed and, once a helpful fairy has reviewed them, they will be implemented. Unfortunately, I am not skilled or experienced enough to do that myself. Sorry.
Please understand the situation.
Hopefully, it's not a hothead.
Best regards,
Klaus
edit: I've uploaded the logs.

At higher speeds and loads, the boost pressure and intake air mass appear to deviate further and further from the target values. Then, the boost pressure control suddenly changes rapidly (possibly indicating a limp-home mode?).
"That's definitely not a leak; with a hot clamp, I wouldn't expect the pressure to drop like that (although I lack the experience to be certain)."
I would rather look for something in the area of VTG regulation, or perhaps something that acts as a "throttle."
Is the intake path clear, and are the particulate filter and catalytic converter okay?
Is the vacuum reading still okay even with a hot engine and under load?
"If you create another log, please include data on acceleration in 5th gear, along with the corresponding fuel injection amounts. Before the test, clear the error code and drive the car in a way that the error doesn't reappear until you reach the actual test (in 5th gear)."
hg
Herbert.

Hello Herbert, thank you for your review and feedback!
Heute Abend habe ich nochmals ein Log im 5. gemacht, von 1500 bis in den Notlauf bei 150 km/h. See LOG.
I also have the injection quantity data for the MWB40.
Hopefully, it will be useful.
As far as I can see, the intake is good and clear. The air filter isn't new, but it's also not excessively dirty.
I'm going to set up a vacuum gauge for measuring pressure while driving tomorrow.

Hi,
The log is less helpful now because it lacks the reference values for the LD (likely referring to a specific process or parameter) and the control signals for the LD. It's evident that there was a significant drop in both the LD and EM (likely referring to another process or parameter) after the LD and LM (likely referring to other processes or parameters) decreased.
hg
Herbert.

I also considered that, but I chose the MWB 10 because it was mentioned in ULF's recommendations regarding LD problems, which I reviewed again.
You're right, I'll try again using MWB 11.
Shouldn't the VTG's TV also be visible there?
If the back pressure after the catalytic converter/DPF is too high, the target value (TV) should increase as a result.
Which sensor displays the DPF pressure difference? Because a clogged DPF also shows up with high values there.

A question - does the model have a throttle valve?
hg
Herbert.

Yes: In addition to the electric EGR valve, there is also an electric shut-off or throttle valve.
Okay, you're right, if it were partially closed, it would also reduce the flow rate. But I was thinking it might be a shut-off valve that only closes when the device is turned off.

Hello...

"Remove the throttle body and check if the valve itself is broken and stuck in the closed position at the back."

I've seen this problem twice now on a T5.
Both performances weren't particularly good overall... meaning there was a lack of quality.

SG
Alevuz.

hello
- I removed the throttle valve along with the EGR valve, and all the valves are intact (it would have been great if I had found what you described there, thanks for the tip). However, the EGR valve was just caked with grime, which I cleaned off. I also made sure the valve stem was smooth and clean. The actuator motor with its gearbox is also audible when you open or close it gently. I lubricated that area.
- When a vacuum gauge is connected directly to the VTG valve with a Y-connector, it always shows -0.8 to -0.9 bar during full-load operation, and it quickly recovers to normal if the brake pedal is repeatedly pressed while idling.
Around the turbo, even on the wave section leading to the VTG (Variable Turbine Geometry), there's a significant amount of soot, making it difficult to see from below. There might be a potential leak of either turbocharger air or soot, either in that area or on the exhaust manifold on the far right.
Due to traffic conditions, only one vehicle with a 4-speed transmission could be processed for AGR cleaning this evening.

The log doesn't reveal anything new. After a short period under load, the boost pressure and air mass decrease, first slowly, then noticeably. As the difference between the target and actual values increases, one can also observe a decrease in the injection quantity (which is controlled by the EDC). The control of the boost pressure system changes little (until the gas is cut off?), and the vacuum pressure is correct.
I would like to exclude:
- Leak on the suction side; otherwise, the LM would be low and the LD would be high.
- Leak on the pressure side; otherwise, the laser power (LM) would be high and the laser diode current (LD) would be low.
- If the AGR (Exhaust Gas Recirculation) system were open, the engine would produce more soot, which is contradicted by the lambda value.
- electrical fault in the control system.
- Leak on the exhaust side, after the turbocharger, which shouldn't affect the supercharging process.
It also doesn't seem to be the throttle valve, which is another potential cause on the intake side.
I can only think of:
- Change in the vacuum pressure within the sensor due to increasing temperature, which causes the VTG (Variable Turbine Geometry) to adjust.
- a leak in the exhaust system, located before the turbine wheel (it opens due to hot exhaust gases, and traces should be visible).
- Clogging of the particulate filter or the catalytic converter (which should normally be noticeable with increasing exhaust flow).
hg
Herbert.

Thank you, Herbert, for your contribution/help with the problem.
I'm having trouble understanding what you mean by "referring to the change in the vacuum sensor with adjustment at high temperature." The vacuum pressure indicated there decreases from -0.6 to -0.2 bar as the engine speed increases under full load.
Ideally, the vacuum should be adjusted at the VTG (Variable Turbine Geometry) valve so that the boost pressure remains constant and only decreases when it exceeds the target value. I could try inserting a Y-connector there and increasing the vacuum to see if the VTG then increases the boost pressure again, or if the turbo control/VTG is completely failing. However, that wouldn't necessarily reveal the root cause.
My direct tasks are to remove the DPF catalytic converter and then work on the turbocharger. The nuts in the manifold area are heavily corroded, and I'm afraid the studs might break.
How can I check/display the clocked signal at N75 without an oscilloscope?
To check for any potential damage in the supply line. I can re-examine the supply line for signs of damage caused by martens, and if necessary, completely remove the outer casing.
The soot around the turbo seems the most suspicious to me. Perhaps a camera could initially monitor the soot buildup and the VTG (Variable Turbine Geometry) rod during its operation.
Do I have a misunderstanding, or should the vacuum pressure at the VTG (Venturi Throttle Geometry) sensor increase if the boost pressure doesn't reach the target value?
I need to check again which measurement unit is used for exhaust pressure.
The pressure difference values should increase when the DPF is closed.

In this case, the differential pressure across the DPF would have to increase, as the measurement is taken before the DPF and vented to the atmosphere (although I don't remember the specifics of our BPC system, I believe it may have measured pressure both before and after the DPF, which wouldn't change the fundamental principle).

Unfortunately, I don't have any logs at full load to give you an indication of the differential pressure. However, please log the data. If it's too heavily populated, you should be able to find the differential pressure readings in the measurement data.

Quote:

Regarding the note about changing the vacuum sensor with adjustment for hot conditions, I'm not sure what to make of it. The vacuum pressure indicated there decreases from -0.6 to -0.2 bar as the engine speed increases under full load.

"At what exact point? During the decrease in boost pressure (until the difference is approximately 250 mbar)? At that point, the control of the variable turbine geometry (VTG) is still so consistent that the vacuum should only change slightly."
You can insert markers during the logging process.

Quote:

I could try introducing a Y-connector there and creating more vacuum to see if the VTG (Variable Turbine Geometry) can increase the boost pressure again, or if the turbo control/VTG is completely at its limit. However, that wouldn't necessarily reveal the root cause.

Be careful, you could unintentionally cause the turbocharger to over-rev.

If the vacuum pressure in the VTG sensor begins to drop significantly, even with continuous activation, this is a clear indication of a fault in the vacuum system or the pneumatic components of the charge pressure control.

Another possible cause that came to mind is a hose collapsing on the suction side.
hg
Herbert.

Quote:

If the vacuum pressure at the VTG sensor starts to decrease significantly, even with continuous activation, this is a clear indication of a fault in the vacuum system or in the pneumatic system of the charge pressure control.

Okay... that's why you should measure the vacuum directly at the source while the vehicle is running. It's possible that a different component, which is controlled later, is leaking, which could then cause the entire vacuum system to fail.

The vacuum in the VTG (Variable Turbine Geometry) generally decreases as the engine speed increases, even before the LD (Load Demand) is reached. This behavior is determined by the software and is designed to allow for more precise control.

Quote:

The underpressure at the VTG generally decreases as the speed increases, even before the LD (Load Detection) is reached, and this is determined by the software to make the regulation more sensitive.

What one naturally sees/must see when controlling the control valve.
hg
Herbert.

Thank you for the participation of more knowledgeable people!
During the journey:
- Vacuum pressure: -0.9 to 0.8 bar, sufficient.
- Supply to N75 also connected to the pressure accumulator, does not collapse.
- After the system is turned off, the vacuum pressure remains at -0.8 bar for a while.
after the throttle valve was pulled down by 0.1 bar when closing.
- The boost pressure drops starting at approximately 2400 mbar. The difference between the target and actual pressure at the VTG (Variable Turbine Geometry) sensor is -0.5 bar. When the target pressure is 2400 mbar and the actual pressure is 1800 mbar, the vacuum at the VTG sensor is only -0.32 bar, and the engine then goes directly into limp mode (the EGR remains constant at 100% TV, while the VTG control continuously decreases to approximately 45-43%). Everything seems okay until approximately 50% TV (Throttle Valve opening) and -0.4 bar at the sensor.
- Leaving the intake open didn't make any difference.
To me, it looks like the STG is already seeing enough LD and is starting to back down.
The ambient air pressure of 980 millibars seems reasonable.

- DPF loading is at 65.
- The differential pressure rises to approximately 80 (is it even worth removing the DPF in this case?).