TDI AHU ; 00575 - Saugrohrdruck Regeldifferenz | Posts 16+

Hi,
Is this the original VW repair manual, or an "internet RLF" (repair manual)?
I'm asking because the 1Z engine is tested at a lower RPM range. The 1Z and AHU are essentially the same engine. I don't have my documents available at the moment, but it should be checked from 1500 rpm to 3000 rpm.
Without the N75 valve, when using a turbocharger controlled solely by the wastegate, the MSG (Motor Steuergerät - Engine Control Unit) primarily checks for overboost.
"Intake manifold pressure regulation difference" usually indicates that the boost pressure is too low for the amount of air being drawn in (due to a leak or a faulty sensor).

The inflation of the STG was very clever . You were only supposed to disconnect the vacuum line from the throttle body and blow compressed air through it with the engine running!
hg
Herbert.

Hello Herbert.
Thank you for the information. I only inflated the control unit because I wanted to check if it was measuring the correct pressure.
The instructions say to use external measurement equipment, but I don't have access to any.

But at least this error is now mostly fixed, and I also replaced the hose to the control unit.

I have the original repair manual for the Caddy TDI with the AHU engine.
In the "Charging" section, the procedure for checking the turbocharger boost pressure control is described.

"Accelerate" the car in 3rd gear from 1500 RPM, then read the value at 3000 RPM -> Target value: 1650...2000 mbar.

-> In my pressure measurements, I'm getting a reading of around 1900 millibars.

And then measure with a calibrated N75 gauge, from 3500 RPM to 4000 RPM.
Set point: 1500 mbar to 1650 mbar.

Unfortunately, I was only able to measure up to 3200 RPM, and I ended up somewhere around 1660 millibars.

What values did you enter for "1Z" in the guide? Could you please check that for me?

As my colleague mentioned, I will measure the target pressure again.

Hello,

The 1900 and 1660 millibar readings you measured seem plausible. Unfortunately, they are not saying whether everything is working as it should.

By comparing the target value and the actual value, you can easily see whether, in the event of an error, the boost pressure is too high or too low...

And please, do not take measurements at a red traffic light, but rather in the operating condition where the error occurs.

Best regards, Rainer.

Hello Rainer,
"Thank you."
Is MWB 11 sufficient? It shows the target and actual boost pressures, as well as the engine speed.
Do I need another one, or should I get something else?

Thank you.

MWB 11 is suitable for charge pressure control.

Quote:

I have the original repair manual for the Caddy TDI AHU... In the "Charging" section, the following is described: "Check the boost pressure control." "Accelerate" the car in 3rd gear from 1500 RPM, then read the value at 3000 RPM -> Target value: 1650...2000 mbar. -> In my pressure measurements, I'm getting a reading of around 1900 millibars. And then, using a calibrated N75 gauge, measure from 3500 RPM to 4000 RPM. Set point: 1500 mbar to 1650 mbar

As I mentioned before, I currently can't access my old RLF (presumably a tuning device). However, I'm confident that even without the N75 valve (likely a pressure control valve), running in 3rd gear with full throttle will accelerate from 1500 to 3000 RPM, and a boost pressure of around 1600 mbar should be achieved. That makes sense because the wastegate is opened by the boost pressure/pressure sensor.
hg
Herbert.

Hello.
I took another measurement today using the MWB 11 device.
VL - Acceleration (in 3rd, 4th, and 5th gear).
What can be observed is that above 3000 RPM, the actual pressure is always higher than the target pressure. At 4000 RPM, the pressure is 120 mbar too high.

The duty cycle is 91.6%, which means the N75 valve is no longer being activated, and the wastegate is trying to open fully.
I also took measurements with the N75 disconnected, and in that case, the base pressure was around 1650 mbar, so it should be able to regulate, right?

He didn't record the error for me today, but when exactly will it be recorded?
What should I watch next?
"Thank you."

Hi,
In my opinion, the boost pressure regulation at 120 mbar is perfectly normal.
Can you reproduce the error with the disconnected plug on the N75 control valve? It takes some patience.
Here are some things you can still do:
- Check the ease of movement of the wastegate.
- Check the adjustment of the actuation rod.
- Check and empty the pressure vessel (as grime and debris can accumulate there).
hg
Herbert.

Hello,

Normally, the target boost pressure is reached in less than 2 seconds from 2500 rpm. If you had logged the data as described in the manual, it would be possible to assess this properly. Sure, here's the translation:

"For example, using KDataScope."

I can only guess, but it seems likely that your wastegate is stuck in a partially open position.



Best regards, Rainer.

Hello Herbert, Rainer.
Thank you for your information.

"Could you please clarify what you mean by 'reproducing the issue of a disconnected connector at the N75 control valve'?"

How exactly can I check the wastegate? Are there any specific pressure values that indicate when it should start to move or open?
How can I "empty" the pressure vessel?

Is there any chance of getting the wastegate to function properly again?

Quote:

Therefore, I can only speculate that your wastegate is stuck in a nearly-open position.

Consequently, it would not be able to achieve the target boost pressures.

Quote:

Could you please clarify exactly what you mean by "reproducing the issue with the disconnected connector at the N75 control valve"?

Drive with full boost while the connector is disconnected.

Quote:

How exactly can I check the wastegate? Are there any reference values for the pressure at which it should move, or the pressure at which it should open?

Have you already done it. Measurement taken with the plug disconnected.

Quote:

How can I "empty" the pressure vessel?

Extend and operate manually.
You either have a leak or a faulty reading with that error.
hg
Herbert.

Hi.

Quote:

Quote: I can only guess, but it seems likely that your wastegate is stuck in a partially open position. Then he would not be able to achieve the target boost pressures.

Okay, just don't call it "almost open," call it "half-open."

My guess is that the wastegate is sticking or not moving freely. This explains, on the one hand, the delayed build-up of boost pressure, and on the other hand, the slightly increased boost pressure at high engine speeds.
And eventually, it ends up being configured in such a way that the deviation from the rule leads to an error entry.

Best regards, Rainer.

Hello Helmut, Rainer.

Go full throttle with the plug pulled.

I actually already did that, but only up to 3200 RPM, and based on the way it's trending, it doesn't seem like anything more is happening at higher speeds.

I'll be putting the car on a lift this weekend; you really can't reach the turbo from above.

I just read that it should start moving when the pressure reaches 0.6 bar on the pressure sensor.
Can anyone confirm this?
The theory about the difficult/stuck WG (working group) seems plausible to me.
Thank you for your help.

Hi,
The boost pressure is perfectly fine. It shouldn't be any higher, otherwise the wastegate won't function properly. Around 1.6 bar is the limit. You can see that in the RLF (likely referring to a gauge or display). The N75's overboost control is the only way to allow the boost pressure to reach approximately 1.9 bar.
hg
Herbert.

Good morning.

Since the weather was so nice today, I decided to do some measurements with my "reference vehicle," a Golf 4 Cabrio ALE.
3rd and 4th gear acceleration.
The engine is relatively similar in terms of things like TL (presumably referring to technical specifications or similar).

In this case, the target value is being properly regulated at the top end, and the N75 valve isn't even being fully activated. It seems like the other person is having a problem with their wastegate.

Hello.

I've now replaced all the pressure hoses to/from the N75 valve.
Then I pressurized the pressure vessel multiple times with 2 bar, and over time, the WG strut moved more and more smoothly.

It looks like this now:
My theory is that due to the inaccurate reading caused by the hole in the pressure hose in the control unit, the wastegate was virtually never adjusted, and therefore it became increasingly stiff.

I will let you know if I can still reproduce the error.

Thank you for your help.