Diesel Filter Whistle: AXR Engine, 6800km, Fix

Hi everyone,

'After my auxiliary heater was installed at a so-called 'specialist workshop,' I've noticed that my diesel filter sometimes whistles. (I admit, I might not have noticed it before. After a visit to a workshop, I always become hyper-aware.) No diesel is leaking. The noise is speed-dependent.'
I suspect that when the diesel line was being installed from the tank to the auxiliary heater, some lines were opened, which are now drawing in air. Also, the fuel is being drawn from the vehicle's tank, which means that tank was also removed (another potential source of error?).

Edit: A phone call with the workshop that installed the part revealed that the fuel tank was never completely removed. Only the fuel level sensor was removed to allow for the installation of the fuel probe.

However, all the pipes are thick and black, so I can't check for air bubbles anywhere. What should I do now?
Another symptom: The car's speed is limited to 180 km/h on the highway (more precisely: the engine doesn't rev above 4000 RPM under load. When idling, it easily revs beyond that). The engine exhibits extreme, repeated jerking at 180 km/h, which is slightly less pronounced when going uphill.
Error memory is empty.

As soon as I turn on the ignition, the motor inside the throttle body housing/mass airflow sensor housing hums continuously. Why? If I disconnect the corresponding connector, the motor stops, but an error code is logged: '~Motor open or short to Ground' (It's reassuring to know that the engine control unit can log errors.)

Here's what else I've noticed: There's a small hole, about 2mm in diameter, in the plastic of the fuel filler neck. I previously thought that this hole was designed to drain any diesel that might drip out when the fuel nozzle is removed from the filler neck. However, I've now noticed that when refueling, just before the fuel pump shuts off, diesel foam comes out of this hole. Is this normal? Does the hole actually lead directly into the tank? And isn't there a risk that water could get into the tank through this hole?

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

'Micha'

Hello!

So, in cases like these, I would ask the "specialized workshop" to redo their work.
Ears are ringing...

Quote:

I also noticed something: There is a small hole in the plastic near the fuel filler neck, with a diameter of approximately 2mm.

So far, I thought that the hole was designed to drain any diesel that might drip out when the fuel nozzle is removed from the filler neck.}

Regarding this, I can say that when my unit was delivered, this hole was present and was quite long.
The "plastic snout" was sealed with a transparent cover (my old Golf didn't have this).
(I pulled it out just out of curiosity). My dealer also didn't know anything definitive.
So far, it's still working.

Regards,

Peter.

Bee wrote:

Der Motor am Abstellklappengehäuse/ Luftmassenmessergehäuse surrt fleissig vor sich hin, sobald ich die Zündung einschalte. Warum?

Where exactly?
Is it the throttle valve (which is a bypass valve in the AXR engine) or the mass airflow sensor?
These are two completely different locations.
Der Motor an der DK wird per PWM angesteuert, daher summt der recht laut. Bei mir auch. That's normal.

Quote:

Here's what else I've noticed: There's a small hole, about 2mm in diameter, in the plastic of the fuel filler neck. I previously thought that this hole was designed to drain any diesel that might drip out when the fuel nozzle is removed from the filler neck. However, I've now noticed that when refueling, just before the fuel pump shuts off, diesel foam comes out of this hole. Is this normal? Does the hole actually lead directly into the tank? And isn't there a risk that water could get into the tank through this hole?

There are even two holes in the fuel filler neck! One is inside the filler neck and is only visible when the cap is removed, and the other is located in front of the cap, in a sort of recess. The first hole is for venting the fuel tank, while the second directs any fuel that overflows from the filler neck down into the wheel well and onto the road. Foam coming from the first hole is normal during refueling, but it's less common with the second hole.

Hi,

Thank you for the answers!

@Peter: Regarding this, I'm in a difficult position: Do I give the 'specialist workshop' a chance to fix it, with the risk that my almost new car will be further damaged (scratched fender edges from the zipper, lifting the car at the fender to fit rubber buffers, a cascade of blown fuses causing a Climatronic error, etc.), or do I go to VAG and have them investigate?

@Bertil: Regarding your question: 'Where exactly?'
Answer 1: It has 'Pierburg' printed on the housing (That's why I thought it was a mass airflow sensor).
Answer 2: A thick, black, flexible hose comes from the intercooler. This hose connects to a metal flange. The connector I'm referring to is located on the side of this flange, at the bottom, and it's quite difficult to reach when the plastic hose is attached.
Antwort 3: Bertil, Du hast in einem anderen Thread ein Bild von Deinem AXR drin. Link: https://community.dieselschrauber.org/en/viewtopic.php?t=8071
I mean the black plug located in the lower quarter of the image, in the center.
I'm referring to the hole in the reservoir, which is visible even when the fuel cap is screwed on. If it's the 'wheel arch drain,' then diesel shouldn't be leaking out of it. When the tank is removed, is it possible to incorrectly connect the two hoses for fuel venting and the 'wheel arch drain,' or is it impossible due to different diameters?

Regarding the engine on the DK: Does it also make a humming noise when the ignition is turned on?

Thank you for your previous responses.


Regards,
Micha.

Regarding the hoses: If the fuel tank were removed in a workshop, I would say anything is possible. Foam could never come out of the overflow hole. Try this test: take some diesel with a syringe and flush it through the hole. But first, place a container under the other end of the suspected hose. If the hoses are swapped, some diesel should always leak out of that hose during normal refueling.

In Bertil's picture, you can see the throttle valve he mentioned, which, according to his description, also causes noises in his vehicle. On my ASZ (engine), I only have a shut-off valve, and I only hear the sound of it opening shortly after the engine is turned off.

Hi Mathias,

I will try out your testing method tonight, when I get home.
Thank you for this tip.

Does anyone have any other tips regarding the whistling diesel filter?

Regards,
Micha.

Hi,

Legal question: A workshop has the right to provide corrective work. What happens if the workshop is unreachable or on vacation? Do I actually have to wait until their vacation is over?

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

'Micha'

Bee wrote:

Answer 1: There is a Pierburg logo on the housing (That's why I thought it was a mass airflow sensor).

Pierburg doesn't just manufacture mass airflow sensors. By the way, the AXR engine has a BOSCH mass airflow sensor.

Quote:

Answer 2: A thick, black, flexible hose comes from the intercooler. This hose connects to a metal flange. The connector I'm referring to is located on the side of this flange, at the bottom, and it's quite difficult to reach when the plastic hose is attached. Antwort 3: Bertil, Du hast in einem anderen Thread ein Bild von Deinem AXR drin. Link: https://community.dieselschrauber.org/en/viewtopic.php?t=8071 I mean the black plug located in the lower quarter of the image, in the center.

Okay, so the DK.

Quote:

Regarding the engine on the DK: Does it also make a humming noise when the ignition is turned on?

I already answered that above and explained why.
Again: YES!

Hi,

@Mathias: The check using your method revealed: The hose is correctly connected. (Now I wonder what I saw while refueling.)

@Bertil: Regarding the DK motor: I wasn't sure from your first answer whether the motor only makes a humming sound when it's running, or as soon as the ignition is turned on. That's why I asked for clarification. Now it's clear to me. Thank you for your repeated answer and your patience.

Still, there's the whistling diesel filter. Any ideas?

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

'Micha'

Hi,

Here's the tentative solution to the problem: My car has been at the VW dealership for two days for troubleshooting. The information provided is what the workshop has told me:

The exhaust gas recirculation system and tandem pump (I can't recall the rest) were checked; everything is okay.

The fuel pump showed increased power consumption, so it was replaced.

And now for the kicker: I got into my car, turned on the ignition, and was completely startled: A buzzing and gurgling sound came from under the rear seat for about 1 second! I had never heard that sound before (and I'm extremely sensitive to noises)! This was the first time the diesel pump in my car made itself known!

I'm incredibly relieved! Even though the workshop said they couldn't clearly identify the cause of the shaking before starting the work, and they're not 100% sure they've solved the problem: I'm really optimistic! I have to admit that my extremely negative impression of VW, which I had after many minor issues, needs to be revised in a positive direction.
A welcome side effect: The harsh jolting sensation during the transition between power mode and low-load injection is also gone!

Finally, one last question for the experienced ones:
Is it possible that, for whatever reason, the diesel pump in the tank is faulty and only delivers a very small amount of fuel. As a result, the tandem pump has to draw more fuel. Under heavy load, the suction capacity is not sufficient, so the engine does not receive enough fuel and misfires (--> jerking).


Regards,
Micha, the happy one.

Bee wrote:

.... And now for the kicker: I got into my car, turned on the ignition, and was completely startled: A buzzing and gurgling sound came from under the rear seat for about 1 second! I had never heard that sound before (and I'm extremely sensitive to noises)! This was the first time the diesel pump in my car made itself known!

That's how it should be... and the noise of the pre-pump is sometimes extremely loud.

Quote:

.... Finally, one last question for the experienced ones: Is it possible that, for whatever reason, the diesel pump in the tank is faulty and only delivers a very small amount of fuel. As a result, the tandem pump has to draw more fuel. Under heavy load, the suction capacity is not sufficient, so the engine does not receive enough fuel and misfires (--> jerking).

It is quite possible.

@Bertil: That is how it should be
That's exactly what I mean! I was just surprised because I'm quite sure that sound has never been there before (meaning, not from the beginning). My constant 'passenger,' who hardly pays attention to sounds, asked me this morning: 'What was that noise?'
Anyway, I wasn't allowed to take the defective pump with me (I would have *loved* to disassemble it to see what was wrong with it), as it needs to be sent back to VW.

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

'Micha'