Intake Manifold Pressure Error: What to Do?

Hello,
I installed an AFN engine (from a Passat B35i, manufactured in 1996) into my T3 van, and I'm apparently having problems with excessive intake manifold pressure (my suspicion!).

At high RPMs, the power suddenly disappears, the car feels like it has a naturally aspirated engine, and error code 0575 - Intake manifold pressure - Control difference (VAG-COM) appears in the memory. Otherwise, it's a lot of fun to drive .

"The boost pressure easily reaches 2500 mbar. (The limit is supposedly 2250 mbar, if I'm informed correctly). I haven't recorded the exact curve (and therefore the maximum value) yet. It doesn't seem to be a problem for short periods (seconds) or at lower RPMs, but above approximately 3800 RPM, there's a "limitation," which seems to happen even without aggressive acceleration. The error message can only be cleared after restarting the engine. After restarting, the car runs normally again until the next acceleration attempt."

Sure, here is the translation of the text from German to English:

"Info:"
I don't know if the previous owner modified the engine, but I suspect (or rather, hope) not.
The mass airflow sensor is new. The intercooler comes from a larger diesel engine and has significantly shorter flow paths.
The VTG loader has been cleaned and is easy to move.
The charging control valve is new and shows a maximum reading of 94.2%.
When the engine is cold, it smokes excessively when I accelerate, but otherwise it doesn't smoke much. When the engine is warm, I haven't observed any such smoking in my rearview mirror, especially when looking against the light.
When the engine is warm, it's very difficult to start, requiring a lot of cranking. When it's cold, it starts immediately, but that could also be due to another cause...

And now, the questions .

What does the error message actually mean? (The consequence is obviously a fail-safe mode.)
Should we limit the pressure, and if so, how?
What could the prolonged organ sound during startup mean?
What other helpful metrics should one measure?
Is there a way to tell if the engine control unit (ECU) has been tuned?

Certainly. Here's the translation:

"Thank you very much."
Carsten.

Intake manifold pressure control difference = The boost pressure cannot be regulated.
Valve duty cycle for turbocharger boost pressure control 94.x% = The MSTG (presumably a control unit) is trying to reduce the boost pressure, but unfortunately, it is not succeeding. This could be due to a VTG (Variable Turbine Geometry) rod being too short, or a problem with the VTG control system/vacuum actuator (e.g., sticking or malfunctioning).

That will be 69 euros, please, payable within 14 days.

Sure, I will use the search function next time.

Thank you for the paid tip .

Perhaps the VTG rod was moved during cleaning.
How is it supposed to be configured? Should the clock frequency always be 100%?
Do you attribute the 94.x% value to the error margin or the pressure of approximately 2500 mbar?

hello
Carsten.

Hi,

Search function -> Enter 'VTG AND setpoint difference'.
Warning: This is reading material for many enjoyable hours.
The duty cycle should not reach either the upper or lower limit.
Ideally, keep it somewhere between 10% and 90%.

Best, Andy.

Yes, thank you very much.
The reading material is really comprehensive; I'll start by gathering and measuring data.
I'm still not quite grasping the concept of the standard time signature, but I'll figure it out eventually.
still


Regards,
carsten

Hello Carsten,

The timing ratio cannot be 0 or 100%, but a maximum of, for example, ~95%. So, if you are measuring at 95%, the MSTG (presumably a control unit) will attempt to adjust the turbocharger control valve (which is a three-way valve) in such a way that no vacuum reaches the VTG (Variable Turbine Geometry) actuator, but instead, air is drawn from the hose to the air filter.
If, however, the VTG sensor remains in the "Maximum Boost Pressure" position even though there is no longer any vacuum present, and you are giving it a lot of gas, then the boost pressure will exceed the limit defined in the MSTG, and the system will enter emergency mode.
Check the VTG valve/mechanism for smooth operation, also test it under hot and cold conditions. As a test, replace the magnetic valve with the one from the EGR valve.
Check vacuum hoses for kinks or crimps.
Take a look at Ulf's technical article on Steuerpneumatiken (Steuerpneumatics), and then you'll see that controlling the boost pressure isn't so complicated after all.

Best regards, Rainer.

I'm starting to get really frustrated with this problem.

Things have improved somewhat after various measures were taken, but ultimately, the difference in regulations with the emergency mode still comes into play.

While checking the impeller, the check valve was noticed. It was stuck and allowing flow in both directions. With the new valve, it was possible to achieve somewhat higher speeds.

I then conducted test runs, both with and without the hose connected to the boost pressure sensor. With vacuum applied, the boost pressure is always above the target value. Without the hose, the boost pressure is always below the target at low RPMs, but it exceeds the target again from approximately 3000 RPM. In both cases, the control difference eventually occurs.
Without the vacuum, the acceleration is only slightly worse, especially below 2000 RPM.
I also tried disconnecting and reconnecting the AGR hose, but I didn't notice any effect.

I also performed the actuator diagnosis, and the valve moved the adjusting rod and the VTG (Variable Turbine Geometry) perfectly.

I then checked the free movement of the VTG (Variable Turbine Geometry) and the pressure sensor individually. Both are extremely easy to move, and it probably couldn't be any better. I had initially thought that something might have broken inside the turbocharger, but you can hear the difference with and without vacuum.
The upper part is achieved with negative pressure, while the lower part could potentially be adjusted slightly more, but I don't think it's worth the effort.

I suspected that the MAP sensor might be giving inaccurate readings, so I temporarily blocked the hose leading to it. Then, it only measured atmospheric pressure, with no signs of erratic values.

Okay, now let's talk about the LMM (likely referring to a Lambda Measuring Module or similar). The actual values are always significantly higher than the target values. Because the part is new, I've always attributed this to the turbocharger running too fast. However, I've now reinstalled the old part, and the values are closer together, and a significantly higher speed is achieved. But the limp-home mode still occurs.

Does anyone else have any ideas?

To the best of my knowledge, Large Language Models (LLMs) and loaders don't have much to do with each other.

Can you please create a log file for block 011?

In other threads, we have been able to much more effectively pinpoint the location of defects remotely using files like this one.

m;

Oops, read before posting (this was directed at me).

Quote:

Without the hose, the boost pressure is always below the target value at low RPMs, but it goes above the target value again from around 3000 RPM.

No hose connected to the VTG canister?
Then the VTG (Variable Turbine Geometry) is affected, because without underpressure, a functioning compressor will operate at "zero pressure."

But you've ruled that out before using a process variable diagnosis!

Objection

Hello,
Yes, that's exactly what I thought too, but it's not the case. That's why I'm still hesitant to try Rainer's suggestion about adjusting the control rod. Because what's the point of doing that if the values are already too high even without creating a vacuum?
And the adjustment mechanism is definitely located at the bottom; there's no interference there. If you separate the rod and the lever, the adjustment becomes so easy to turn that you might think something has broken off.
The vacuum sensor is also movable without any jolts and has a spring mechanism; therefore, it pushes the lever downwards when there is no vacuum applied.

As I said, the loader was cleaned by a qualified technician. Is it possible to assemble something incorrectly, such as having the guide vanes misaligned, forgetting a spring, or something like that?

Another possibility is that the engine control unit (ECU) is misreading something. However, the car seems to be running okay otherwise, as far as I can tell. The only issue is that it tends to produce a lot of smoke when accelerating, especially when the engine is cold. This is probably due to excessive pressure with the corresponding fuel injection, but the problem disappears when the turbocharger hose is removed.

Another possibility is that the modifications might cause the various parameters to become misaligned, such as the mass flow rate, pressure, gas composition, etc. However, to the best of my knowledge, I would be the first person to experience that, which seems unlikely.
The original pipe between the LLK and AGR is 50mm thick and relatively long. Mine is shorter, also 50mm, except for a short bend from the T4, where the connections for the temperature sensor and the boost pressure hose to the control unit are located; that part is 55mm. However, I can't imagine that this would affect the pressure measurement, especially since the original rubber hoses still fit with a little squeezing (and are certainly sealed there ).

"In the log for block 10 or 11, I noticed something strange: At a constant speed, and therefore a constant target pressure, the actual pressure suddenly jumps up and then tends to be higher than the target pressure. Where could this be coming from?"
"It seems to me that the duty cycle reaches 94.2% after a steep increase, and then the pressure suddenly increases."
Otherwise, there are no indications of any irregularities.

I now have plenty of logs, both with and without the turbocharger pressure connection. I'd be happy to send you some if you'd like.

Does anyone know what the criteria are for the emergency mode? What values are allowed to deviate by how much? The mass airflow sensor (MAF) will play a role because it influences the target value. By the way, a new MAF sensor measures so much more, unfortunately, costing 180 euros. How can you even rely on anything anymore?
Does anyone happen to know of an experienced tuner in the area around Goslar? (or Braunschweig or Halberstadt?)

Best regards,
Carsten.

Okay, so if the mass airflow sensor (MAF) is measuring values that are too high, it could be because you have too much boost pressure. The moment the boost pressure exceeds the target value, the amount of air being drawn in will also be higher than the target value. Therefore, you need to compare the MAF sensor readings to the target pressure values when the boost pressure is also at its target level.

I think the problem lies with your boost pressure control system.
Check if the voltage drop across the control valve during operation corresponds to the expected control behavior.

If that's the case, and the valve is okay, then check the vacuum hose.

If the VTG (Variable Turbine Geometry) is stuck, try blinking it by connecting the turn signal wire to the solenoid valve. This will cause the VTG to constantly switch between its minimum and maximum positions.

Hi,
Thanks for the tip, I'll give it a try, just out of curiosity...

But I think a different factor is more important:
How is it possible that, without vacuum (i.e., without any regulation) and with a free-moving control lever that is almost always in the lowest position, a high boost pressure is still measured and achieved, and that the car performs well as if it had a turbocharger without adjustment?

(Of course, I'm assuming that the lever at the bottom indicates a minimum boost pressure, which is how I've understood it so far, because someone once posted that it's pulled towards the maximum setting shortly after the VTG starts.)

There's something wrong with that repaired loader! Or the measurements are useless, but the engine is running strongly (which makes you worry about the transmission ).

Has anyone ever taken one of these things apart and know if anything can be installed inside?
I know the link to the photo series about the cleaning process, but I can't see from those photos how a lever in the "down" position is supposed to function or how it affects things.
I have prepared two JPEG files with logs, but I don't know how to post them.

Regards,
Carsten.

I have prepared two JPEG files with logs, but I don't know how to post them.


When writing articles, you have the option to click the 'Add attachment' button below. This allows you to attach something to your post.

PS: It's usually easier to read and results in smaller file sizes if you provide the data in a format like *.xls, *.log, or *.txt instead of *.jpg.

Regards,
Private.

Hmm, am I too stupid for a forum???

My profile indicates that I am not allowed to post, I don't see an "Attachment" button, and the FAQ states that it is not possible, or only possible through an external server.
Sorry, I'm an "average consumer," even though I sometimes participate in online forums.

Regards,
Carsten.

Okay, send me the text you want translated.

You already have the private message about that!!

m;

carstenAFN wrote:

Hm, am I too stupid for a forum??? My profile indicates that I am not allowed to post, I don't see an "Attachment" button, and the FAQ states that it is not possible, or only possible through an external server. Sorry, I'm an "average consumer," even though I sometimes participate in online forums. Regards, Carsten

Sure, here is the translation of the text from German to English:

"Addendum:"

I just spoke with the "Turbo Cleaner" support again, and they said it's actually the opposite: the turbo that's not connected is in the "Max" position.
Well, the log seems to be measuring something different, unless the "max" setting on the turbo is so inefficient at lower RPMs that it actually produces less pressure than the regulated setting.

Now, I need to test and check some other things. Then, even if everything seems normal, the vacuum might not be sufficient to regulate the charging pressure, and the position of the control rod will come up for discussion again .

More to come.

hello
Carsten.

Hi there,

Given the excessively high LMM (mass airflow meter) values, I would first question whether the EGR (exhaust gas recirculation) system is functioning correctly.
In my case, the LMM values are also strangely always much too high .
However, this does not affect the boost pressure control.

Quote:

How is it possible that, without vacuum (i.e., completely without regulation) and a free-moving control lever that is 99% in the lower position, a high boost pressure is still measured and achieved, or that the car performs well as if it had a charger without adjustment?

That's simply not possible. Without the vacuum, it drives like a 40 horsepower naturally aspirated diesel engine. In my opinion, there must be something wrong with the turbocharger.

Greetings.
dieter