Boost Overrun 2.5 TDI 163HP - Normal?

Hello everyone,

We did a test run to check if the mass airflow sensor (MAF) was faulty, and this boost curve was the result. Is this overshoot normal? It takes 4-5 seconds for the pressure to stabilize.

The LMM also has this curve... what could be wrong with it - if something *is* wrong?

Best regards,

Overshoot is normal. If you want to get the maximum response from the turbo, it's even unavoidable. However, the first overshoot is quite significant. It's possible that your VTG (Variable Turbine Geometry) isn't functioning perfectly, or that there's a slight leak in your charge air system. It could also be related to the N75 valve.

The subsequent dip after the peak should not have happened either.

Does it sometimes go into emergency mode?

No other abnormalities were detected.
The driver was there because the car sometimes feels a bit sluggish to him.
That's not emergency behavior, though...

"Mine does the same kind of overshooting and also needs about 3 adjustment attempts to reach the target value. You can feel the overshoot in the performance, but I've already given up trying to fix it. The people at VAG don't seem to see it as a major problem. Mine doesn't go into limp mode..."

mserge wrote:

Mine also does the same kind of overshoots and also needs about 3 adjustment attempts to reach the target value. You can feel the overshoots in the performance, but I have already given up trying to fix it. The people at VAG don't see it as that dramatic. Mine doesn't go into limp mode...

The overboost isn't that bad, as long as it doesn't trigger the emergency mode. But the drop in boost pressure is definitely not right.

How many kilometers are on the car?

Mine also does the same thing, swinging back and forth until it settles properly, just like shown in the picture, and it's been doing that for an estimated 50,000 km and 2-3 years. It currently has 185,000 km on it.

I'm familiar with both the overswing and the underswing from my own device. It shouldn't be like that, because yours supposedly has an improved control strategy, but I don't know exactly what was improved.
However, based on my observations, the boost pressure regulation oscillates more frequently and intensely the worse the condition of the engine (particularly the turbocharger) and the fuel injection pump.

It's a shame there's no timestamp on the curve. But does the settling time really take 4-5 seconds? I find that quite long. The overshoot/undershoot is a bit high, but still tolerable. Could you show me some other original examples?

Hello,

Okay, so the car in this example has 154,000 kilometers on it...
However, it received a new engine including a turbocharger at 127,000 km.

Here's a diagram with a timeline...

You can tell that the power starts to fade somewhere between 2000 and 2700 RPM.

SOLUTION: N75 replaced, mass airflow sensor (MAF) changed, and the air filter was clogged!

Hello Legolas,

Did replacing the mass airflow sensor actually improve things for you, or was it just a troubleshooting attempt?

Greetings,
Andi.

Hello Andi,

Replacing the mass airflow sensor (MAF) might not really make a difference for you (except perhaps for slightly improved throttle response), because when the boost pressure drops (underboost), the quantity limitation is just not yet activated. So, it could be the turbocharger, the N75 valve, or the software. Some 2.5L V6 TDIs may have been programmed in a somewhat lackluster way or have bugs, and there have been occasional software updates for them.

Best regards, Rainer.

I also think that replacing the mass airflow sensor (MAF) in my case probably won't make a direct difference. I was just wondering if a new MAF sensor might influence the system in such a way that it reduces the overboost (N75 was already replaced -> no improvement, the air filter was also replaced today, which brought some improvement, but I haven't logged the data to show the change yet...).

I'm just wondering why there's a noticeable lack of power up to 2700 RPM, even though neither torque nor exhaust emissions seem to be limiting factors (and there's not even a hint of soot in the rearview mirror...).

SW is already the latest version available at the company.

Best regards,
Andi.

Does the injection start control work?

Best regards, Rainer.

Okay, I replaced the turbocharger at 200,000 km, and since then, it's been running really well, as much as you can say that about a V6. The lack of power when starting only occurs when the air conditioning compressor is turned on.

Oh yes, with my first loader, the torque converter was worn out. That's why it had trouble getting up to speed and also experienced more overshooting.

I couldn't pinpoint the exact reason why a "kick" sometimes occurred at 2700 RPM. Mine only experienced it occasionally as well.