FehlerCode Saugrohrdruck - Regeldifferenz ? Was nun? | Posts 16+

Here's Carsten's log:

http://www.luxus-wg.de/~martin/auto_bilder/log_mit_unterdruck.jpg

Regarding the topic of vacuum, let's talk about boost pressure.

If someone says that negative pressure REDUCES boost pressure, they are mistaken.

Imagine the vacuum hose has a hole. Then the turbo will immediately start boosting at full pressure.

If the hose bursts at 4000 RPM, the turbo will fail faster than the EDC can reduce the gas flow!

Furthermore, everyone else says that he's using vacuum pressure to achieve boost pressure.

The mechanism operates in such a way that an "increasing vacuum" (decrease in absolute control pressure) results in an increasing charge air pressure. Therefore, this system is fail-safe; if a tube breaks, the turbo will supply a minimum charge pressure.

Here:
http://www.technologie-entwicklung.de/Gasturbines/VNT15-Turbo/vnt15-turbo.html

Hi,

In addition to Martin's post:

If excessive boost pressure is being generated in the higher RPM range, even with the vacuum hose disconnected from the turbocharger, the problem is clearly within the variable geometry turbine (VGT) mechanism, which should ideally be in the "zero boost" position without vacuum.
This condition corresponds to the EDC system's "minimum boost pressure" fail-safe setting. This explains why the system defaults to emergency mode both with and without the vacuum hose connected to the turbocharger.

In practice, although boost pressure is usually not used, a slight amount of pressure is often generated when the engine is brought to 4000 rpm with full throttle - but the pressure must never exceed the target value .

If so, the possible causes could be:
1) Membrane dose clogged due to internal defect (partially) -> Replace the dose.
2) Movement of the steering vanes in the loader is partially blocked due to Russian sediment buildup -> clear the blockage.
3) The diverter mechanism is jammed due to overheating (excessive tuning) -> save up for a new charger.
4) VTG rod set too short -> extend in increments of half turns.

It's actually a fairly straightforward story about error reduction. I'll incorporate it into the section for technical articles.

Here is the second one.

http://www.luxus-wg.de/~martin/auto_bilder/log_mit_unterdruck.jpg
http://www.luxus-wg.de/~martin/auto_bilder/log_ohne_unterdruck.jpg

More data:

Please find the relevant logs attached.

There are several images associated with the tags *ohneturbo1 and *mitturbo1.

"otoarg" simply means without the turbo hose and without the ARG hose.
almmoturbo means with an old mass airflow sensor and without the turbocharger hose.

http://www.luxus-wg.de/~martin/auto_bilder/csv.zip

(@martin: The last link seems to be broken?)


Okay, I just checked again. When the vacuum sensor activates, it seems like the turbocharger is taking on load; the faint whining sound gets louder, and the engine speed drops slightly. So, it's true that the turbocharger is in its minimum position without vacuum.

"So, something must be wrong with the charger, because as you can see from the log "ohne turb1", the pressure is still quite good. Unless someone knows that this is normal when running without the hose..."
Or, alternatively, a slightly leaky expansion joint in the exhaust manifold might not generate enough back pressure. However, I've been told repeatedly that this doesn't matter. (Well, VW does state in the manual that the exhaust pipe should not have any leaks for the correct turbocharger pressure setting?)

"But why use a loader if the lever, when disengaged, moves the normal distance of about 12 mm, and that distance is also within the limits allowed by the can? There's actually nothing wrong with that."

Do I need to remove the charger now because it's apparently charging too well?
In any case, none of Ulf's four logical points seem to apply here.
Does anyone else besides Dieter remember what the effect is in a functioning system when the hose is disconnected? It seems to me that this is the criterion for determining if it's loose .

I can already see the value of a charger being debited from my account.
Where can you buy something like that cheaply, if not from VW?

Regards,
Carsten.

The link is working now - you should also type in the password .

It would be fantastic if a driver with an Audi A4 (AFN engine) and a working system could provide a log file (including Group 11 data and possibly mass airflow sensor values) while the turbocharger hose is disconnected!

Greetings.
Carsten.

carstenAFN wrote:

It would be fantastic if a driver of an AFN engine with a functioning system could provide a log (Group 11, and perhaps also MAF sensor values) with the turbocharger hose disconnected.

Hi Carsten,

I didn't have time to use VAGCOM right now.

I once drove a round with the VTG hose disconnected -> full throttle in 3rd gear from 1500 to about 4200 rpm. (I don't think the air mass values are relevant here; the boost pressure is the main thing, in my opinion.)

Result: At approximately 2500 rpm, the pressure is about 0.4 bar, increasing further to around 0.8 - 0.9 bar at 4000 rpm. Naturally, the engine only started to produce significant power well above 3000 rpm.

Then, the engine control unit even kindly switched into emergency mode. It still managed to reach approximately 0.2 bar at 4000 rpm *yawn... snore*.
By the way, all of this happened without a single blink signal from the light bulb .

Finally, the engine was briefly turned off, and the hose was reattached -> wow, what a suit .

Editor's note

Ulf has a mechanical boost pressure gauge in the cockpit, which is why the values are not from VAGCOM.

m;

Great, thanks for your effort.

Result: at 2500 rpm, approximately 0.4 bar, increasing further to about 0.8 - 0.9 bar at 400 rpm.
Normally, the engine wouldn't produce its full power until well above 3000 rpm.

Am I understanding this correctly: 0.4 bar on your gauge would correspond to 1400 mbar when using VAGCOM, correct? (Assuming an air pressure of 1000 mbar).

Well, at 3000 RPM, it pulled quite well, which also corresponds to my experience. It starts to wake up around 2000 RPM, and later on, it's not so bad at all.

You're probably thinking that the emergency stop is now being triggered due to pressure values that are too low...
I'm starting to get unsure about what criteria the engine control unit (ECU) uses, or in which map it performs the comparison.

I just can't figure out where the problem is with the charger...

Regards,
Carsten.

Okay, so there's some new information...

I once wondered what could cause excessively high pressure in a charger (assuming it's in good working order) when the hose is disconnected.

1. The control unit is measuring incorrectly.
2. AGR valve open (the exhaust pressure is normally higher than the boost pressure, otherwise the exhaust gas recirculation system cannot function).
A little bit of everything.

Hopefully, I'll be able to borrow a pressure gauge soon.

I quickly sealed the EGR bridge pipe with a piece of metal, and lo and behold, with the hose disconnected, there's hardly any pressure anymore, and the log clearly shows how a vacuum is created when you press the accelerator. And the engine noise seemed a bit quieter. Or is it normal for some pressure to always leak through, even with a functioning EGR system?

However, even with the turbo hose attached, the pressure during idle is still significantly above the target value, so it seems there might still be an issue. (I haven't done a test drive yet). In any case, the turbocharger seems to be okay.

Initially, the error code 0519, indicating a "short circuit to positive" for the intake manifold pressure sensor (G71), was stored in the error memory.
"However, it hasn't reappeared, and I've read that this can also occur in conjunction with VAGCOM? (Control unit number: 028 906 021 CK)"
Otherwise, it would smell like a faulty control unit, right? That part is located inside the control unit, so it's unlikely that the wiring is bad... Is it possible to replace individual components?

Is it possible to remove the AGR valve from the intake manifold and replace it, even though VW doesn't officially recommend it?

My engine seems to be a case of many small problems. It's worth mentioning that it came from a car that was involved in an accident, where the driver had to be extracted, but it only has 94,000 km (approximately 58,000 miles).

Greetings.
Carsten.

carstenAFN wrote:

I quickly sealed the EGR bridge pipe with a piece of metal, and lo and behold, with the hose disconnected, there is hardly any pressure anymore, and the log clearly shows how a vacuum is created when you press the accelerator. But with the turbo hose attached, the pressure during idle is still significantly above the target value, so it seems like there's still something else going on. (I haven't done a test drive yet). In any case, the turbocharger seems to be okay.

Hi Carsten,

The AGR story seems to me to be a new, potentially causative aspect -> good instinct on your part .
I consider the fact that the loader runs above the target value when experiencing gas surges while stationary to be (by itself) not critical.
In any case, a proper logging run should still be performed, both with and without the loader control hose attached.

Quote:

Otherwise, it would smell like a faulty control unit, right? The part is located inside the control unit, so you can't have any bad wiring... Can you replace individual components?

I wouldn't assume a faulty STG (Steuergerät) just yet.
The internal pressure sensor should, in my opinion, be easily replaceable (3 wire solder joints and some kind of mechanical fixing on the circuit board) - if you can find a suitable replacement part -> the Bosch part number is printed on the plastic housing of the sensor.

Quote:

Is it possible to remove the AGR valve from the intake manifold, even though VW doesn't provide for it, and replace it?

I'm afraid not. In any case, I would first try loosening it (repeatedly).

'Hello, please check the air mass readings at idle and then apply vacuum to the VTG (Variable Turbine Geometry) control unit. If everything is okay, the air mass should increase slightly at idle. If the readings remain the same, even though the linkage is free, it means the guide vanes are stuck in an aggressive position (possibly due to a defect in the swivel shaft or the linkage connecting to the guide vanes).'
To be absolutely sure, disconnect the charger and take a closer look at it.

Hello,
Okay, first of all, thank you everyone for your strong interest in this issue!

Unfortunately, I didn't get a pressure gauge today, but I did manage to test drive the vehicle and review the user manual.
Now, it reaches 140 km/h for the first time (without the attached charger hose!!!), but then it still goes into emergency mode. And it's not reproducible; on the second attempt, it stopped again at 120 km/h, but with a suspiciously high amount of boost. Maybe the turbocharger impellers are doing whatever they want... Without the charger hose, the boost pressure is beautifully linked to the engine speed in the log at high RPMs .
With the loader, everything depends on how much you accelerate, but it tends to go into limp mode sooner.

It's incredibly frustrating. A log under the same conditions cannot necessarily be reproduced... However, the readings from the control unit are actually plausible, so I will unscrew the loader tomorrow and take a look. It's always annoying the first time because you have nothing to compare it to.

I was just reading about the relationship between the AGR (Abgasrückführung - Exhaust Gas Recirculation) and the LMM (Luftmassenmesser - Mass Air Flow sensor), and I'm going to test that. The LMM values are always significantly higher than they should be. And it's the only part where I extended the original wiring harness, maybe there's a problem there...

If the loader isn't displaying anything, I'll probably have to find a way to get a testing device. Adapting it to WFS seems straightforward...

It's also annoying that I can't determine the reason for the emergency stop from the logs; either the sampling rate isn't fast enough, or perhaps an unacceptable pressure difference is still dependent on another parameter (a characteristic curve).

See you.
Carsten.

Hello everyone,
Okay, the cause of the discrepancy in the settings has been identified and resolved, so dance and be happy...

The turbocharger was assembled incorrectly, unbelievable, right???

What delights tuners is a lesson for those who believe they should get good work for their money: You can either assemble the VTG turbocharger in the normal way, or in a way where the guide vanes are positioned slightly differently. You simply need to rotate the adjustment ring, as the adjustment notch is positioned asymmetrically.

I created a PDF with an image and emailed it to Martin; he's probably a nice guy and will post it .

"Now there's no more blue smoke when accelerating with a cold engine, the pressure readings are stable and differ by less than 20 mbar, and there's no more limp mode, which is great!"
The old mass airflow sensor shows slightly too much at lower RPMs and significantly too little at higher RPMs, but I still have the new one to test.

The downside: The top speed is now noticeably lower than before (before the emergency mode). But my T3 transmission will probably thank me for it . However, I need to rethink that long gear ratio I was aiming for...

"As a test, I removed the turbocharger hose again, and it's as Ulf said: it only starts to function normally at 3000 RPM, and then quickly goes into limp mode. However, I can't confirm what Dieter once wrote about it being limited to only 40 mph."

Okay, so, once again, a heartfelt thank you to everyone who contributed their ideas. Now, I will also send an email to the turbo mechanic! If I can arrange for some compensation, say the value of a small spare part (after all, it took 1 week of searching and half a tank of fuel for test drives }), I will pass on that amount!

Best regards,

Carsten.