T4 2.5 TDI: Power Loss Above 130 km/h

Hello,

"Recently, I've been experiencing a problem with my van (T4, 2.5 TDI, ACV engine, 200,000 km, 1997) where it's no longer reaching its maximum speed."
When accelerating in the lower gears, you get full power.
Nothing's moving there.
I can also drive in third gear at 4000 RPM for a longer time without losing power.
But then, on the highway, it reaches its limit at 130 km/h (approximately 80 mph), with the engine at 3000 RPM.
"That's when the good one goes into limp mode. The error log once indicated that the engine control unit was locked."
It's not the LMM; I already have the bypass diode installed.
In addition, the reading from the VAG COM device was 850 mg/…
The linkage for the turbo vacuum actuator is still moving.
What can I check, test, or log again?

Best regards, Klaus.

Hi,

If there's an emergency stop, then there will always be an error log entry. Unless it's been tampered with, where someone has simply modified the file.
It's best to read the error codes immediately after the emergency stop and avoid repeatedly triggering the error.

If the air mass is okay, there's not much else to check. Make sure to check the start of injection, the target vs. actual values, and the turbocharger pressure control (refer to maintenance manual section 11).
Hopefully the diesel filter is new, which means the fuel supply should be sufficient.

Best regards, Rainer.

Okay, so no tuning is possible, and the fuel filter is about 25,000 km old and has definitely not been exposed to biodiesel or rapeseed oil.
Today, I felt like connecting the LTop again.
You were right again, there's an error.

Control unit part number: 074 906 021 L
Component and/or version: G00SG 1450
Encoding: 00002
Workshop code: WSC 02744.
1 error code found.
00575 - Intake manifold pressure.
17-10 - Rule difference - Sporadically.


Should it perhaps be a pressure sensor?
Or what does this error message mean? I don't have a VTG charger.

Best regards, Klaus.

Hi,

Sure, it could be the pressure sensor, the hoses, or the solenoid valve... so check everything and, while it's running, see what's causing the problem, i.e., whether the pressure is too high or too low (compare the setpoint value with the actual value in measurement block 11).

Best regards, Rainer.

Hi,

I logged in today.
But what does that tell me?
Setpoint/Actual Value Comparison: How can I identify this when one value remains almost constant?
I only noticed that the duty cycle jumped from 12.8 to 68, and then the oven turned off.
Okay, the rod from the vacuum sensor seems to be moving properly. However, the blue vacuum hose looks a bit porous to me.
Please explain it to me.

Best regards, Klaus.

Hi,

As you can see from the log file, you are using a suboptimal label file from Autointern. Due to the corrupted part, you cannot recognize anything, because the column names are incomplete.

In measurement block 11, values 2 and 3, you'll find the target value and the actual value of the boost pressure. The actual value is likely always close to atmospheric pressure, which means either the boost pressure sensor is faulty, the hose connected to it has come loose (if applicable), or your wastegate is always "open."

Best regards, Rainer.

Ouch...
'I saw similar values last week at an AFN where the charger had malfunctioned.'
(Bearing failure due to oil shortage).
If you're lucky, only the pressure hose connected to the MSTG is damaged or detached.

Best regards,
Rudi

[edit] You were faster, Rainer [/edit]

Everything is really running suboptimally.
Regarding the wastegate.
I had the engine replaced 25,000 km ago.
After the installation, I had absolutely no turbo boost pressure in any driving condition.
After thinking about it for a while, I then came up with the idea of using a vacuum sensor.
The bracket had been slightly bent during installation.
So, the WG valve was always open.
After being repositioned, the vehicle started working again.
Now I have the performance data, and it seems the issue starts at 140 in the fifth gear and gets worse from there.
I'll probably take another look at it.
Is there a limit?
Why is the target pressure in my LOG increasing by a minimum of 40 mbar?
Best regards.