Strange humming noise on ASZ TDI PD engine

'I've noticed a strange humming sound coming from my engine for the past few days!'
...I'm not talking about the idle vibrations; I also experience those occasionally with a warm engine!
I mean the following:
'The engine is fully warmed up, and I'm driving, for example, in second gear at a constant 40 km/h. Then I take my foot off the gas and lightly tap the accelerator again, and it makes a loud rumbling noise. I'm not sure if this is normal; it sounds like a throttle valve opening without an air filter, just louder and more unpleasant. The car only does this when the engine is fully warm, and always when I release the gas? I initially thought it might be related to my engine control unit, but I've also tried driving without it.'
.....does anyone have an idea The kilometer reading is 5,500 .
Regards,
Monchi.

MONCHI wrote:

For example, I drive in 2nd gear at a constant speed of 40 km/h, then I take my foot off the gas and lightly tap the accelerator again, and it makes a loud rumbling noise... The car

always when you release the accelerator.
Hi,

I'm spontaneously guessing it's some kind of scraping metal or something.
Can you reproduce the noise at the same RPM in other gears, or at the same speed in other gears?

And when exactly does it start buzzing? Completely without gas, or with minimal gas usage?

Hi,
Take a look at this, it's an A3, and it's only in afterburner mode, but maybe it's something in the right direction?
Okay, I'm ready. Please provide the German text you want me to translate.

And when exactly does it start buzzing? Completely without gas, or with minimal gas?

.....it only makes a buzzing noise when I release the accelerator; as soon as the engine is under load, it disappears!!
.....it's most noticeable in 2nd gear, between 1,500 RPM and 2,500 RPM. If I give it a little gas and immediately take my foot off the accelerator, it's also there!
Regards,
Monchi.

...I need to revisit this topic.
...the buzzing is still present, I've now taken some time to try and locate the source.
...the humming sound only occurs when the engine is REALLY warm!!! (and then it gets progressively louder until it reaches a certain level).
...the humming occurs regardless of engine speed... but it depends on the position of the accelerator pedal!
...the humming occurs when I release the accelerator, and it also happens when I give it just a little bit of gas and hold that position, in which case it hums constantly!!!
...what I've already tried: a piece of foam placed between the pipe from the air conditioning system and the fuel filter housing (this has helped some ASZ drivers with similar problems).
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...I removed the plastic engine cover and drove without it... no change!
.....Does anyone have any idea why my engine is making such a loud noise??
Greetings
Monchi.http://mitglied.lycos.de/matcherman/s1.jpg{MARKER}

Hello!

I am a beginner .
'I have the same 'problem' with my Polo 9N - it only happens in the summer.'
only when the engine is warm!

At 2000 RPM, if you let off the gas before a traffic light, you'll hear a humming sound.
If I heard correctly, it's coming from the right side, in the direction of travel. It is about...
to power the AXR PD with 74 kW. When I accelerate again, it's gone.
What also surprises me is when I drive with the windows open and I can hear the car from...
Let's say I let it coast at 70 km/h, I can still hear the sound of the charger .
It should have already engaged the automatic shut-off... why can we still hear the loader?
still... strange

Has anyone found a solution for the buzzing sound (it sounds almost like something is vibrating)?
Does the engine cause bloating?

...in my case, the problem had a completely different cause!!
...it was because of my winter tires!!!!!!!!!!!!!!!!!!!!
...when I randomly decided to check the DOT codes on my used winter tires, I discovered that one of the tires had no DOT code visible at all!
The reason was that the tire was mounted incorrectly, with the DOT code facing inwards (while only 'inside' was visible on the outside).
...that was the reason for those noises. Since I switched to my summer tires, the problem has disappeared!
Mileage is now 18,000.
Greetings
Monchi.

TheBeer wrote:

..... It is the ATX PD model with 74 kW.

ATX What kind of engine is that?
As far as I know, the POLO only comes with the ATD or AXR engines, both with 74 kW.
I am, however, open to being proven wrong .

Quote:

What also surprises me is when I drive with the windows open and I can hear the car from... Let's say I let it coast at 70 km/h, I can still hear the sound of the charger . It should have already engaged the automatic shut-off... why can we still hear the loader? still... strange

The charging process will continue for quite some time. And you will only stop hearing it when the exhaust flow is truly close to zero. Even when operating at idle, "exhaust" passes through the impeller blades and drives the turbine blades, although not as forcefully as under load.
The thrust reverser does not interrupt the flow of gas through the turbine; the engine essentially functions as an air pump.

Bertil wrote:

... The turbo cutoff disables only the exhaust valve, not the gas flow through the turbo. The engine essentially functions as an air pump.

Does it also close the storage compartment lid? Operating as an air pump would, at the very least, be a losing proposition.

joegolf wrote:

Does it also close the storage compartment lid? Operating as an air pump would, at the very least, be a loss-making venture.

Normally not.
Why should operating the air pump result in a loss compared to operating with a closed shut-off valve?
The opposite is the case:
The engine's intake process creates a vacuum, regardless of whether the turbocharger is active or not.
A closed bypass valve would create unnecessary resistance to the engine's intake airflow, resulting in more wasted kinetic energy compared to simply operating the engine as an "air pump."
If you were to disconnect the valve lifter (closing the intake valves), the situation would be different, but this is currently the case for very few engines.

ATX What kind of engine is that?
As far as I know, the POLO only comes with the ATD or AXR engines, both with 74 kW.
I am, however, open to being proven wrong .


Oops, sorry, I didn't move my fingers as much as my head wanted to.
Sure, AXR should be there!

I guess I'll have to take a look at the right front tire – it's not like it's winter.
it might therefore come from the summer tire .

It's good to hear that the whistling sound from the turbo is normal, as I've only been driving this car for 14 months.
TDI (although mostly my girlfriend drives it), but when I do drive it, I notice quite a few things.
I got a new car, and previously I had an A3 1.8T with 180 horsepower, where I didn't experience this whistling sound before.
It's also a slightly different principle of operation .

Thank you for the quick responses!

Bertil wrote:

joegolf wrote: Does it also close the storage compartment lid? Operating as an air pump would, at the very least, be a loss-making venture. Normally not. Why should operating the air pump result in a loss compared to operating with a closed shut-off valve? The opposite is the case: The engine's intake process creates a vacuum, regardless of whether the turbocharger is active or not. A closed bypass valve would create unnecessary resistance to the engine's intake airflow, resulting in more wasted kinetic energy compared to simply operating the engine as an "air pump." If you were to disconnect the valve lifter (with the intake valves closed), the situation would be different, but this is currently the case for very few engines.

If I haven't made a major conceptual error here, the air isn't just being drawn in, but also compressed. If it's not ignited (i.e., in a thrust-producing mode), the air will expand again and push the piston downwards. This process should, however, be lossy, no matter how small the loss.
With the bypass valve closed (and generally, using abbreviations like AGR), the maximum vacuum that can build up is limited. In that case, the effect of the air spring would indeed be smaller, but so would the losses .

joegolf wrote:

.... With the bypass valve closed (and generally, using abbreviations like AGR), the maximum vacuum that can build up is limited. In that case, the effect of the air spring would be smaller, but so would the losses

.

However, this only applies to a system that is 100% airtight, and you won't be able to achieve that with a car engine.
Therefore, the losses caused by the air pump effect are smaller.

TheBeer wrote:

.... Oops, sorry, I didn't move my fingers as much as my head wanted to. Sure, AXR should be there!

Some AXR models are known to be noisy.

Bertil wrote:

A closed bypass valve would mean that you are creating unnecessary resistance to the engine's intake, so more kinetic energy would be wasted compared to simply operating in "air pump" mode.

Hi Bertil,

For me, the "compressor function" is more easily understood.
The cylinder filling pressure is relatively low (meaning there is a vacuum behind the shut-off valve), but when ejecting, the motor pumps against a significantly higher pressure = external pressure = 1 bar.

-> Therefore, the motor not only functions as a pump, but also as a compressor, and the latter requires significantly more power.

Hi,

Okay, I'm familiar with this problem from studies involving racing engines.
In the slide throttle mechanism, the throttle valves are slightly opened because the power loss caused by a closed throttle, due to compression and intake losses, is greater than the power loss with an open throttle.
Why was that the case?
The only explanation is that the loss due to the closed DK is higher than the "compressor function" alone.
I just can't understand why it should be different for diesel engines.