Major problem, emergency mode

Hello, I'm new here. I hope someone can help me. So far, no one has been able to help me in the A4-Freunde forum or on Motor-Talk. But here I am, among diesel experts .
Okay, for about 3-4 weeks now, my engine (Audi A4, new model, 1.9 TDI PD, 130 hp, with KW-Systems Powerbox, approximately 160 hp, 38,000 km) has been going into limp mode at full throttle, around 130/140 km/h. It also happens with slower acceleration, around 180/190 km/h. It happens even without the tuning box, so it's not the box causing it, just a bit later. I've checked everything with my friend: we replaced the mass airflow sensor, renewed the vacuum hoses, checked the boost pressure (everything is within the normal range), etc. We also made sure the VTG adjustment is working properly. Nothing has helped. Oh, and there's always an error code in the diagnostic memory: 'BOOST PRESSURE REGULATION LIMIT EXCEEDED.' I hope someone here has some advice for me, I'm completely desperate. I've found similar problems using the search function, but they haven't really helped me.

Best regards,

wacken wrote:

Boost pressure checked (everything within normal limits), etc. . . . Oh, and there's always a fault code in the error memory that says "BOOST PRESSURE EXCEEDS REGULATION LIMIT."

Hi.

So, these two things are fundamentally contradictory.

Can you perform a test drive with VAGCOM data logging and post the values (specifically, when the limp-home mode is activated)?

You probably still have a warranty, right? Should Audi bother with that?

Unfortunately, the warranty has already expired; the car was manufactured in January 2001. I need to look into the values and the test drive; I'll ask my acquaintance again.

Best regards,

Okay, so we couldn't print anything out, but we measured the exact boost pressure, and at the moment the limp mode kicks in, it's 2346 millibars. However, it also happens in 2nd and 3rd gear when you're giving it full throttle, but nothing happens then; it only occurs in 4th or 5th gear. Speeding at approximately 140 km/h?????

Best regards,

wacken wrote:

So, printing wasn't possible, but we measured the exact boost pressure, which, at the moment the limp mode starts, is 2346 mbar. However, it's the same in 2nd and 3rd gear at full throttle, but nothing happens there; it only occurs in 4th or 5th gear. Speeding at approximately 140 km/h?????

Hi.

I'm not sure what to do about that either; the pressure seems to be (still) within the acceptable range.
"First, I would adjust the VTG rod to be slightly longer (this will reduce pressure spikes a bit and costs nothing). If that doesn't help, then I would replace the boost pressure solenoid valve."

First of all, thank you. We have already replaced the boost pressure solenoid valve.

Best regards,

I have another question. For a few months now, my TDI has been experiencing occasional brief jerks, as if the engine cuts out for a fraction of a second. It only happens sometimes. What could this be, and could it be related to the limp mode?

Best regards,

Hi,
For a few months now, my TDI has occasionally experienced a brief jolt, as if the engine cuts out for a fraction of a second.

That sounds very much like the needle valve governor (NHG) is the culprit.
There's a lot of information available on that topic through a search function.

Could that also be causing the problem with the emergency mode?

Best regards,

Hi,

Command retracted. I just read that you have a permanent magnet (PM) motor, of course.
As far as I know, they don't offer any NHG products anymore.

But look at it this way: If it's already broken, it can't break any further – which, to be honest, is something it tends to do anyway.

Hey Markus, did you also manage to get the curve? I actually wrote about it yesterday, explaining that it's the NHG, then describing the knocking method, and then I read the entire thread and deleted my post.
I also missed that. Funny It would have fit so perfectly...

@wacken: What does the error memory say after you've experienced that jerking?

Markus H. wrote:

Hi, Command retracted. I just read that you have a permanent magnet (PM) motor, of course. As far as I know, they don't offer any NHG products anymore. But look at it this way:

Then it can't break - which is something it really likes to do.

Hi Markus,

Well, I can't entirely agree with you on that.
The PD motor still has NHGs. However, it no longer has one, but four:wink: . The PD elements are being "misused" as NHGs. The EDC (Electro Discharge Control) can detect the needle stroke based on the coil current of the PD (Piezoelectric Discharge) element.

However, it is true that the PD no longer has a true NHG (Naturally Aspirated High Output) engine like the ones we are familiar with from VP engines.

However, if a PD element is faulty, there should be a different error code stored in the control unit.

In this case, I suspect the VTG (Variable Transmission Gear) is either stuck or misadjusted.

I once heard about a similar case.
There, at a certain speed under full load, the motor went into emergency mode. In his case, it was a misconfigured...
Accelerator pedal position on the sensor. He then exceeded the maximum speed, which triggered the emergency mode.

Perhaps you could have the sensor alignment checked.

'These 'stuttering' or 'hesitation' issues only occur sporadically. Initially, it was mainly when it was cold (the engine and the weather), but now it happens more frequently. The only error code stored in the diagnostic memory is related to the limp-home mode: 'CHARGING PRESSURE EXCEEDED LIMIT'.'

Best regards,

Hi,

You should take a look at the duty cycle of the magnetic valve used for turbocharger boost pressure control.
Have you tried Ulf's suggestion yet? It's possible that the increased fuel injection volume caused by the boxer engine prevents the VTG (Variable Turbine Geometry) adjustment from being mechanically retracted far enough.

Best regards, Rainer.