Boost Pressure at Idle & Delayed Boost Build-up

Hello diesel mechanics!

I have a question.

Since I'm currently working on improving the performance of my A3 1.9 TDI 110 HP (with a chip) because the power output is not optimal below 2000 rpm, I realized that there's also a lack of boost pressure at idle.
It should be around 990 mbar, but VAGCOM shows a reading of approximately 880 mbar.
The LMM (likely referring to a mass airflow sensor) is okay, and I've cleaned out the significant amount of EGR sludge.
I replaced the entire turbocharger boost and EGR hoses, and since then it hasn't been producing any more soot.
Could it be that the loader isn't getting enough power because it's running at too low a speed?
If so, what else could it be due to?



Best regards.

Bertl.

hello bertl

It's possible that the boost pressure sensor could also be faulty.

and constantly report an excessively low boost pressure to the control unit.

Best regards.

hb2000

Then your turbo would already be generating a vacuum relative to the ambient pressure when idling?
I can't imagine that. You should check the boost pressure sensor; perhaps the ambient pressure isn't being measured correctly either. I believe it's integrated into the MSG (Main System Module) in the AFN engine and cannot be replaced individually. If that's the problem, you'll need to find a new control unit.
Do you have access to a VAG Com interface? If so, please post the readings from blocks 3, 8, and 11, as well as the ambient pressure reading.
Does the car run normally?

Zak1976 wrote:

Then your turbo would already be creating a vacuum compared to the ambient pressure even when idling??? I can't imagine that

.
...but it is fundamentally possible: If the VTG (variable turbine geometry) is open due to a defect, the compressor stops, and the impeller acts as an obstruction to flow.

Quote:

Do you have access to a Vag-Com interface? If so, please post the readings from blocks 3, 8, and 11, as well as the ambient pressure reading.

For sensor checks, it's better to briefly check the MWB 10 while the engine is running, as you can see the ambient and boost pressure there. A difference of up to approximately 20 mbar is still acceptable; above that, one of the sensors likely has a problem.

The target values for both are calculated from the current weather report, minus the local altitude above sea level (1 millibar per 8 meters of elevation).
It should be noted that the 8-bit resolution allows for display increments of only approximately 10 to 12 millibars, which corresponds to roughly 100 meters of altitude, depending on the software.

On the highway, when I gently press the accelerator, it feels like the car switches from constant power to tuned performance. (When I gently press the accelerator).
When you floor it, the power is available "instantly."
I will double-check the measurements and adjust them accordingly.

Can someone tell me exactly where the boost pressure sensor is located?
I read that he should be somewhere at or near the LLK.

Best regards.

Bertl.

Bertl100 wrote:

Can someone tell me exactly where the boost pressure sensor is located? I read that he should be somewhere at or near the LLK.

On the A3, as far as I know, depending on the model, it's either located at the top of the air intake manifold (LLK), or in the intake manifold between the intercooler (LLK) and the engine. In any case, it's where a 4-pin cable leads .

I replaced the pressure sensor, but there's no change in boost pressure.
When the engine is idling and at a standstill, the sensor reports 870 mbar below block 10 in VAGCOM.
When accelerating, the maximum power is still reached at approximately 2100 rpm, just like before.

Bertl100 wrote:

I replaced the pressure sensor, but there is no change in boost pressure. While idling and with the engine off, the sensor reports 870 mbar under block 10 in VAGCOM.

And what does the comparison between intake manifold pressure and boost pressure reveal when the engine is idling?

This problem is driving me crazy because I've been searching for the error for so long.
I would like to repair it myself, but nowadays the only thing that seems likely to be the problem is the turbocharger, which I definitely can't fix myself.
The hose from the coolant reservoir to the EGR valve is fine, and I can hear the turbo starting around 1300 RPM, but the boost pressure just won't build up.

The atmospheric pressure is 970 millibars with the engine off, which is the same as when it's idling.

Bertl100 wrote:

I would like to repair it myself, but nowadays, almost only the turbo is likely the problem, and I definitely can't work on that myself.

If the difference between the boost pressure and atmospheric pressure is this significant even with the engine idling, it can't be solely due to the turbocharger.
If a new load cell sensor provides similarly incorrect values, I would unfortunately have to try a different measurement and control unit (MSG) next. Before that, however, I would check the wiring harness as a formality, although I can hardly imagine any fault that could reduce the read load cell pressure value by approximately 100 mbar.
Or could someone have attempted an LD (laser diode) "fake" tuning?

Here's the translation:

This is a company optimization project by "upsolute".
Is it the same with the original chip regarding boost pressure?

Best regards.

Bertl.

Okay, I have another question now.

I don't know how long this has been happening, but when I accelerate, I hear not only the sound of the turbocharger but also a kind of whistling noise. Is that normal, or could there be a leak somewhere?

Best regards.

Bertl.

Bertl100 wrote:

This is a company optimization project by "upsolute". Is it the same with an original chip regarding boost pressure?

"By 'fake tuning,' I mean a resistor, a diode, or something similar placed in the wiring harness between the sensor and the control module (MSG)."
Someone could have cobbled that together independently of the chip...

ulf wrote:

Zak1976 wrote: Then your turbo would already be generating a vacuum relative to the ambient pressure even when idling??? I can't imagine that . . . . but it is fundamentally possible: If the VTG (Variable Turbine Geometry) in the LL (Low-Pressure turbine) is open due to a defect, the compressor stops, and the impeller acts as a flow obstruction.

Even when idling with the VTG (Variable Turbine Geometry) vanes fully open, the engine rotates; after all, the engine still produces some exhaust energy even at idle.
Let's look at two numerical values: Turbocharger speed at idle is approximately 10,000 RPM with the variable geometry turbine (VT) open, and approximately 30,000 RPM with the VT closed.

Okay, even if the VTG (variable temperature gauge) was activated, values below 900 millibars are absolutely implausible.
unless you are at an altitude greater than 1000 meters above sea level (for every 1000 meters of altitude, the ambient pressure decreases by 100 millibars).
I'm simply ruling out the Application Traceability Log (ATL) as a potential cause of the error here, because if it were the problem, we would likely be seeing more errors, such as Low-Level Data (LLD) underflows or overflows.