Passat Power Loss: Troubleshooting & Solutions

hello

I drive a Passat TDI with 90 horsepower, manufactured in 1996, and it has already covered 230,000 kilometers.
'Naturally, he doesn't have the same performance as he did at the beginning. However, I would like to know if there's anything that can be done to restore the performance to something closer to what it was. It's hardly noticeable anymore when the turbo kicks in at 1800 RPM. The mass airflow sensor (MAF) is working correctly. Which parts are likely to be wearing out the most? What parts would need to be replaced? Do ceramic additives help, or is that all just nonsense?'

Hi.

Are the fuel filters, etc., in good condition?

Depending on the mileage, the intake manifold may be quite clogged with soot and oil sludge, which can restrict airflow to the engine.
Perhaps the AGR valve is no longer closing properly.
You can read the background information in the relevant article on agricultural technology.

The turbocharger pressure control valve also tends to cause problems more frequently in the 90 horsepower engine.
Do you have an LDA on board?

What's the compression like? Have you already done the minimal test for mobile use?

Sure, no problem.

Okay, so the filters are all fine, and the performance is consistently bad. Unfortunately, I don't have LDA.
How does the 'minimal test for travel' work?

Hi,
- How old are the fuel injectors?
- What happens to the Russian doll if you step on it?
Do you have a way to use VAG-COM (for reading error codes and measuring data)?

Best regards, Rudi.

tubbietoast wrote:

How does the "minimal test for travel" work?

Hi.

It's mentioned in the used car tips on Rainer's website.

'Thank you.'
This forum is really great!

I think the injectors are probably the original ones, and the Russian development is normal. I might be able to use VAG-COM in my workshop.

Hello,
'I'm experiencing the same problem with my Audi 100, type 44 TDI, with over 260,000 km. The original 120 hp and 265 Nm are barely noticeable anymore. Especially during acceleration (1500-2500 rpm), there's a significant lack of power, and the turbo boost is almost completely absent. I suspect the turbocharger pressure regulator. How can I test it for leaks? Should I disconnect the hose and blow air through it?'

Best regards, Björn.

Hi,
Assuming that the engine of the 44 is quite similar to the AAT, aside from the EGR system, the turbocharger boost control valve is controlled by a pulsed voltage. If there is no voltage applied (engine off or connector disconnected), the resistance should be low when air is flowing through it. If there is approximately 12V applied (engine idling), it must be the case.
Otherwise, the wastegate could also get stuck in the open position. Unfortunately, at least with the AAT, you can't directly observe the actuator rod between the pressure sensor and the wastegate, so the air pump test isn't possible. Instead, I pushed a wire through the connection pipe.
Christian.

Hello Christian,

Thank you for your reply, I will try that.

Wastegate? I know, it's actually a well-known term, but I always thought wastegate = blow-off valve. But I'm not an expert; if that's wrong, please forgive my ignorance .

On the Type 44 (1T), located on the left side of the airbox, next to all the connector plugs, there's a square box and a round box above it. Both have electrical connections and a hose leading to the intake manifold. Is the square one the boost pressure sensor and the round one the control valve? I think it should be the same as on the AAT, except for the EGR and catalytic converter, the engines are very similar.

Best regards, Björn.

Hi Björn,
The boost pressure control valve has a two-pin connector, while the pressure sensor has a three-pin connector. Otherwise, I think you're correct, but I could double-check it on the actual device.
That's a matter of definition. In any case, that's how everyone here sees it.
For understanding: The wastegate controls the boost pressure by regulating the amount of exhaust gas that reaches the turbine. In older engines, the boost pressure from the intake manifold is directed to a diaphragm, which then opens the wastegate. The higher the boost pressure, the further the wastegate valve opens, preventing further pressure increase. From a control engineering perspective, this is roughly a proportional control system.
Unfortunately, such a control loop is not entirely optimal in its behavior, which is why the boost pressure control valve was added. In theory, engines equipped with a boost pressure regulator should reach the target boost pressure at a lower engine speed than those without it.
In practice, the regulation is designed such that, with the AAT (presumably an abbreviation for a specific system), the boost pressure reaches approximately 0.6 bar of overpressure without any intervention from the LDR (likely another component), instead of 1 bar.
Best regards, Christian.

Hello Christian,

Thank you for your detailed answer. I especially like the last sentence ('In practice, the system is designed so that with the AAT, the boost pressure reaches approximately 0.6 bar of overpressure without intervention from the LDR, instead of 1 bar.'). I think that's exactly what's happening with me. I have noticeable boost pressure, but also a very noticeable lack of it. I'll check that out.

Best regards, Björn.

Hello again,

It would have been so nice... I just unplugged the connector from the wastegate control valve: no change in performance, still as bad as before. I'm measuring 0V between the two terminals with the ignition off, and 12-13V with the ignition on and the engine running. That made it clear to me that the valve must be faulty.

Do you think I installed the new one this morning (for 80 euros), and everything is still as bad as before? So, that wasn't the problem. Does anyone have any other ideas? Maybe I'm losing boost pressure somewhere. But I've already checked everything multiple times. Is there a way to do a pressure test?

This weekend, I'm getting a turbocharger and fuel injectors for the car at a good price. I'm going to try installing them, maybe it will make a difference.

Nerve.
Björn.

Hi Björn,

Before you make any further investments, why not just measure your boost pressure?
Measurement conditions:
- Read the value after at least 3 seconds of full throttle.
- Speed: 3000 rpm
- at least 3rd gear

Best regards, Rainer.

Hi,
If there is a loss of boost pressure or air, it can be detected by observing the oil lubrication and increased soot production under higher loads.
When the connector is disconnected from the LDR, it should have a free passage. This results in a pressure of only 0.6 bar being regulated, which corresponds to a low power output.
Unfortunately, this doesn't tell us anything about the function's purpose.
However, the voltage fluctuations are also interesting during normal operation.
As Rainer already mentioned, I would also start by measuring the boost pressure. Then, at the same time, I would measure the voltage at the LDR (Light Dependent Resistor).
Christian.

How can I measure the boost pressure? I don't have a device for that.
Björn.