Level Sensor Connections: Not in ECU?

Hello,

Okay, I have a Passat from the year 1994 with a 1Z engine.

'Recently, I've been hearing a hissing sound behind the speedometer. So, I checked it out today. Since there's no multi-function display (MFA) installed, there's also no vacuum hose connected to the speedometer.'
Also auf der suche wo das wohl her kommt entdecke ich einen möglichen anschluss an einem unscheinbaren kistchen neben der lenksäule. Aber kein schlauch weit und breit. Also ersatzteilnr abgeschrieben und gesucht was das ist und wo man das anschließen kann. Die nummer ist 3A0 906 051. AlThat's the height adjuster.

Using the search function, I only found height adjusters that are located in the control unit.

I'm not sure now whether a pressure tube needs to be connected or not. I don't know if it directly measures the ambient pressure or not.

Okay, so, does anyone know if there's a vacuum hose connected to it, and if so, where does it go?

Greetings.

Hi there!

Why would a TDI speedometer with Multifunction Display (MFA) need a vacuum hose?

You seem to be confusing the TDI engine with very old gasoline engines that "guessed" fuel consumption based on vacuum conditions in the intake manifold.

But 1. diesel engines don't have intake vacuum anyway (that's why there's an external pump for things like the brake booster), and 2. TDIs especially don't have those "mechanical" features, because everything is electronic .

If this part is the altitude sensor, it should measure the ambient pressure and thus be able to calculate the altitude. That means it has a hole somewhere where air is applied, and it electronically reports the altitude to the engine control unit (ECU).

The entire system is designed to significantly reduce power output in order to prevent the turbocharger from being overly stressed in thin air.

To the best of my knowledge, no hose should be connected to this box, and it shouldn't make any hissing sounds.

It's more likely that the pressure hose connecting to the engine control unit (ECU) is leaking. The ECU is located in the water reservoir, which is known to be behind the instrument cluster.

Here's a wiring diagram (for a Volkswagen Golf Mk3), with the engine control unit (ECU) removed.

http://people.freenet.de/golf-schrauber/LDAnschluss.jpg

Okay, please provide the German text you would like me to translate into English. I will only provide the translation.

dieselmartin wrote:

What is more likely is that the pressure hose connecting to the engine control unit (ECU) has a leak. The ECU is located in the water reservoir, which is known to be behind the dashboard.

Yeah, I think so too.

Then the noise should be controllable via the accelerator pedal (-> boost pressure), and normally, the engine's behavior should also change (-> intake manifold pressure regulation difference -> limp mode, etc.).

If the hissing sound occurs regardless of engine load, it's likely due to a leak in the vacuum system, such as the bypass control valve (BKV) or similar components.

Hello,

Okay, the vacuum line to the control unit is sealed.

And even if there was a leak, it would more likely hiss from behind the passenger airbag.

So, the thing about MFA was in the book called 'Now I'm Making It Worse.'

I found a leak in the exhaust gas recirculation system, but I'm not sure if that's what's causing the hissing sound. I'll see if it goes away after I fix it.

But is it normal to have so many soot deposits in the intake manifold?
'Well, it looks even worse than the exhaust manifold.'


I hadn't even thought about the BKV yet, but I'll take a look now.

Greetings.

"Try searching for information on the EGR (Exhaust Gas Recirculation) system and pollution. You'll likely find that even with a properly functioning EGR system, the intake manifold can look quite dirty if it's constantly allowing exhaust gases to pass through, especially if it's been doing so since 1994."

Matthias.

@ Roadagain

to clarify:

The hose to the engine control unit is a pressure hose, specifically a boost pressure hose.
In a 1Z engine, only the brake and EGR systems operate under negative pressure.
The wastegate is controlled by an overboost pressure sensor.

In VTG TDIs, the turbochargers are pressure-controlled.

Okay, please provide the German text you would like me to translate into English. I will only provide the translation.

Hello,

So, after I removed the exhaust gas recirculation system and stuck my finger into the intake manifold boot, it became clear to me that it was completely blocked.

I just disassembled it, cleaned it thoroughly, and also removed the exhaust manifold along with the turbocharger.

I was already wondering why the vacuum pump had so much soot in it, while the exhaust manifold didn't. It seems that's probably normal.


Everything has been freshly sealed and repaired.

The hissing sound is gone now. It's running much better. I just reached almost 180 km/h on the straightaway.

I've also mentioned before that oil leaks out of the pressure hoses.
After taking it apart, I can tell that the problem is coming from the crankcase ventilation system. What can be done to prevent it from releasing so much [exhaust/pressure]?

Sometimes, the performance still drops unexpectedly.

Clearly noticeable when driving on the highway, especially during inclines.
I just drove about 600 kilometers again.

Greetings.

P.S. It quickly became clear during disassembly and testing that these must be pressure hoses.