Boost pressure too high (17-06-2006, 13:55)

Hello.

First, I'd like to introduce myself.

I drive a VW Passat 3BG.
Engine: AVB, 100 horsepower.
160,000 km
Year of birth: 2001.

Regarding my actual problem.

When driven at full throttle for an extended period (more than 10 seconds), it switches to emergency mode. Sometimes starting at 4000 RPM, and sometimes starting at 3000 RPM.
The AGR valve is new. The ease of operation of the VTG (Variable Transmission Gear) was checked, and it is operating smoothly.
And the LMM curve looks strange somehow. The value is greater than the target value.
You can see that the boost pressure exceeds the permissible limit.


Error memory is empty.
What is the problem?http://666kb.com/i/af0g2wo1ormr63qh9.bmphttp://666kb.com/i/af0gcvvhxvdhlpk25.bmphttp://666kb.com/i/af0g52a3vrw7ffpot.bmp

Hello,

It looks like the VTG (Variable Turbine Geometry) is always at full boost pressure. If it feels mechanically easy to adjust, and you've likely noticed this by hand, there might be a problem with the actuator, such as a solenoid valve stuck at its maximum control pressure.

I would first access the basic settings in measurement block 11, where the VTG (likely referring to a valve or similar component) is switched back and forth every 10 seconds. I would then check the loader to see if the VTG rod is actually moving.

If it doesn't happen automatically, you can increase the engine speed to 1300 RPM. At this speed, a pressure difference of approximately 100 mBar should be detectable between the maximum and minimum positions of the variable turbine geometry (VTG).

If it's not moving, the solenoid valve is likely defective, or there may be a problem with the control pneumatics. Incorrectly connected?
If it's moving, it's likely that the rod is completely misaligned.

"Check the boost pressure value with the ambient pressure sensor while the engine is running (I don't have the measurement data block readily available right now) to rule out a faulty boost pressure sensor."

Regards,
Malte.

Thank you for the quick response.
I accessed the basic settings in measurement block 11, and the VTG only moves once, then the rod stops at the maximum (top) position and doesn't move downwards.
At 1300 RPM, the VTG moves downwards.
The difference in boost pressure is greater than 100 mbar; the target is 1010 mbar, but the current reading is 979 mbar.
What do you think it is, the rod or the solenoid valve?
The solenoid valve doesn't click like the EGR valve does.

What now? The VTG rod moves upwards during the initial setup and doesn't return to its original position even after 10 seconds?

Please observe the gauge for at least 1 minute at the default setting and idle speed. It should move approximately 1 cm in one direction quickly and smoothly, and then return to its original position after about 10 seconds.

The default setting switches between full and zero boost pressure approximately every 10 seconds. In this maneuver, the VTG rod must also move back and forth.

When I mentioned the difference in boost pressure at 1300 RPM, I wasn't referring to the difference between the target (setpoint) and actual value, but rather the difference in the actual values when the variable turbo geometry (VTG) is completely closed versus fully activated. Actually, it's also a good way to determine if anything is happening at the charger, especially if you don't have a way to directly inspect the rod.

Okay, try searching for Bertil's posts; he once had a working VTG (a type of railway vehicle), but the vacuum pump was "stuck" due to contamination (I think it was oil).

During actuator diagnosis, the N75 solenoid valve's rod moves back and forth for approximately 1 minute, then it stops in the upper position, even though I haven't canceled the diagnosis.
Thank you in advance.

Hi, I'm new here, but I had this problem two years ago too. I even took the car to the dealer back then, and they told me it was either a faulty solenoid valve or a pressure sensor. I then made another appointment to have it checked more thoroughly, but before that happened, my turbocharger failed. The debris from the turbocharger wheel had spread everywhere. You should definitely hurry, otherwise the same thing might happen to you as happened to me.

sakda7j0 wrote:

During actuator diagnosis of the N75 solenoid valve , the rod moves back and forth for approximately 1 minute , then it remains in the upper position, even though I did not interrupt the diagnosis.

It's possible that the actuator diagnosis only runs for a limited time (but I'm not sure).

Try setting the basic configuration of the MWB 11 (motor in low range), where the "VTG ON / OFF" setting should be displayed in the target field. Precisely when the display changes, the rod should move back and forth -> Any delay in the movement indicates a jam.

Default setting 011.
Speed => 1407 RPM.
Boost pressure min => 1010 mbar at 99.6%.
Boost pressure max => 1244 mbar at 0.0%.

The VTG rod moves back and forth.
Could you please check the values and let me know if they are correct?

sakda7j0 wrote:

Could you please check the values once and let me know if they are correct?

Yep, the values seem to be correct so far.
As I said, the other question is whether the rod moves quickly, smoothly throughout its entire range, and immediately changes back and forth with the display.
For that, you should really "put the Lappi on the engine," or, for example, hold a test lamp against the VTG solenoid valve.

Okay, so I basically had block011 enabled, and the rod moved as described, with the display changing smoothly and instantly back and forth.

I have one more question, and that is, can the LMM be broken?

sakda7j0 wrote:

I have one more question, and that is, can the LMM be broken?

Then the boost pressure would certainly not be too high, as indicated in the title .

"Why don't you try swapping the EGR valve with the boost pressure control valve? They have slightly different calibration maps, but that might work. Then let us know if it makes a difference; if nothing changes, the valve is probably okay."
If you want to be sure whether the VTG (variable turbine geometry) is stuck or not, the safest method is to remove the turbocharger. Furthermore, you can then open the exhaust side and see how the VTG vanes look and whether the mechanism that controls them is jammed. Cleaning often works wonders and can potentially restore the car's lost "appeal" or "excitement."
If the pressure sensor is defective (e.g., the membrane is torn, stuck, or leaking), the only option is to replace the entire unit. Spare parts are not available.
Are all the hoses for the vacuum system connected correctly? This can also lead to the most bizarre errors.

Hi,

You still haven't checked the boost pressure sensor, at least to see if it's giving a reasonable reading with the engine off.
Measurement block 10, fields 2 and 3 should be approximately the same. One is the boost pressure, and the other is the ambient air pressure.

Please check the vacuum hose connections according to the plan outlined in the technical articles here.
It appears that the VTG is functioning properly.

So, if the turbocharger pressure sensor is working correctly, then it's most likely that the variable geometry turbocharger (VGT) control rod is completely misaligned. What other reason could there be for the LD (likelyhood score) to become so high?

Or the rod moves, but the guide vanes in the loader no longer do .

Has anything been done about that yet? What could be the cause of incorrectly connected hoses or a misaligned VTG rod?

Okay,

The actuator diagnosis is also time-limited for me. However, the basic attitude apparently hasn't changed.

Regards,
Malte.

HI

I measured data block 10 today.

Air mass: 235.2 mg/R
Absolute pressure: 989 mbar
Absolute pressure: 989 mbar
Load: 0.0%

I'm not sure if anything has been changed. I've had the car for a year. I haven't performed any repairs yet.