Whistling at idle

My 66 kW TDI engine makes a whistling noise after a short time when idling. For example, when I come home from work and park the car with the engine running in front of the garage to open the door, you can hear it. It's particularly noticeable coming from the exhaust. When you stand on the side (driver's side), you can hear it a little quieter. In the engine compartment itself, you can only hear it faintly in the background. However, it's difficult to pinpoint the source in the engine compartment because the knocking sound is louder. If I briefly press the accelerator, it's quiet for a few seconds. After that, it starts again softly and gradually increases in volume.

What could that be?

Your car has a turbocharger, and that noise is normal.

Hello,

just to clarify things a bit:

If my AFN's engine hasn't warmed up yet, it makes a whistling sound with a significantly lower frequency from the exhaust pipe. I think the cold oil might be creating more resistance for the impeller, which is why the charger is running at a lower speed when idling.
Am I correct with this explanation, or is there another reason for it?

There are alternatives, though.

It's possible that the oil pressure in the supercharger is building up too slowly (ouch), which is why the shaft is running slower when it's cold. In that case, I should also be able to hear the supercharger clearly whirring loudly from the engine bay under load, right? Besides, I doubt he would have survived that for very long...

Could it be that the VTG (Variable Turbine Geometry) doesn't always close completely, causing the turbocharger to spin up faster at idle (resulting in a higher-pitched whistle)?
Under normal driving conditions, the subjective feeling of torque delivery is unremarkable, and the maximum speed is not an issue. I still remember the driving experience with VTG trailers from my previous Passat (also with the AFN engine).

Unfortunately, my adapter has a problem, and I can't even check the boost pressure curve or the duty cycle from the LDR using VAG-COM because I can't establish a connection to the control unit while the engine is running.
Connecting an analog ADR would require drilling a hole in the pressure pipe, and unfortunately, I don't have time for that right now.

Perhaps someone can shed some light on this matter.

Regards,
macro

makrospex wrote:

If my AFN hasn't warmed up yet, it whistles with a significantly lower frequency from the exhaust pipe. I think the cold oil might be creating more resistance for the impeller, which is why the charger is running at a lower speed when idling. Am I correct with this explanation, or is there another reason for it?

In my opinion, this is the most obvious one.

Quote:

Could it be that the oil pressure in the turbocharger is building up too slowly (ouch) and that's why the shaft is running slower when it's cold?

The turbocharger will have oil pressure again within a few seconds after a cold start. Until then, it has to rely on the residual oil from the previous run. Therefore, the tip: don't press the accelerator immediately after a cold start!

Quote:

Could it be that the VTG sometimes doesn't close completely, and therefore the charger runs faster in idle mode (resulting in a higher whistling sound)?

If it doesn't close completely, the loader needs to rotate slower -> producing a lower tone.

Hi Ulf,

Thank you for the response.

Quote:

The turbocharger will have oil pressure again within a few seconds after a cold start. Until then, it has to rely on the residual oil from the previous run. Therefore, the tip: don't give it any gas immediately after a cold start!

I always let the engine run after a cold start until the hydraulic lifters stop making noise. These vary between four and ten seconds, depending on the season.

Quote:

If the valve (VTG) doesn't close completely, the impeller needs to rotate at a lower speed -> producing a lower tone.

Okay, then I didn't mean it completely openly, I unfortunately always mix that up .
I'm going to experiment with the VTG soon. When the engine is cold and idling, I should be able to see if the VTG might be sticking sometimes.
Unfortunately, I need some help with that; you can't hear the whistling from the beginning.

Eventually, I'll have to drill a hole in the pressure pipe and install my LDA (Linear Drain Adapter).
Driving without an LDA (Lane Departure Assist) system feels wrong; it's missing a crucial control feature for me.

Regards,
macro

@makrospex
as I understand it:

Quote:

Could it be that the VTG sometimes doesn't close completely, and therefore the charger runs faster in idle mode (resulting in a higher whistling sound)?

If the VTG adjustment in the LL (likely referring to a variable geometry turbine) is not set to fully closed (not tightened enough), the turbocharger will spin slower than it should.

My VTG strut is in the closed position (maximum pressure buildup).

ok,

Now I understand .

I'll try to get my adapter working properly soon.
Without VAG-COM, performing diagnoses and tests is definitely a disadvantage.

Regards,
macro

'How do you people in this forum repeatedly come to the assumption that the VTG (variable turbine geometry) must be completely closed in idle? I know, for example, that in my case (I think I've mentioned this before), it only closes completely when the duty cycle is also fully at 0. That's why it's never completely closed in idle – only during the VTG basic position test.'

Devilseye503 wrote:

For example, in my case (I think I've mentioned this before), these only close completely when the pulse width is also fully at 0. That's why they never close completely at idle - only during the basic position test of the VTG.

AFAIK, the VTG (variable torque governor) starts to close completely at around 20-25%, which can be inferred from my MWB 11 logs.

Did you turn your VTG rod for a longer duration? Or is your pump no longer producing its full vacuum?

No, Ulf, everything is still original. It's not running at full pressure at 20%. The vacuum was measured and is also okay. At the pump, the vacuum is around 800 mbar at idle, and after the control valve, it's around 600 mbar, so that's fine.

That's why I'm writing this - otherwise, VW would just have to install faulty parts.

Devilseye503 wrote:

everything is still original - at 20%, it's not fully at maximum pressure. Vacuum measured - also okay - around 800 mbar vacuum at the pump at idle, and around 600 mbar after the control valve - so it's okay

Funny: my LD-TV also shows 20% in the LL mode, and the VTG is set to its maximum (IIRC, it's been a few years since I tried this).

Quote:

otherwise, VW would have to just install shoddy parts

Only or partially, that is the question...

Can your VTG lever be moved further towards the closed position with little force when in the LL (low-load) position? If so, the VTG rod is likely set too long (for some reason).

"Mine definitely runs at full power (at least when I tested it in late summer), which is why I wrote that. But I'm not even sure about my vacuum pressure; it might even be too low. I don't know if yours or mine has a problem. Mine, anyway, has what I consider to be a too-slow pressure build-up (but that's off-topic), so I'm glad that mine isn't like yours." Then it would probably be even worse.

Can your VTG lever be moved further towards the closed position with little force when in the LL (low-load) position? If so, the VTG rod is probably set too long (for some reason).

I can't answer that question directly about the force, because I didn't remove the pressure sensor (and I don't want to... it's original). I can only assess it by feeling how much force I'm applying against the spring inside the sensor, and in that case, I don't notice any difference. Also, the pressure sensor is controlled with a duty cycle of 0% (full vacuum), and in that state, it behaves as if it's in the default setting, going all the way. Unfortunately, I haven't been able to test this phenomenon on another identical motor yet. However, the workshop says that this is normal.

Devilseye503 wrote:

ulf wrote: Can your VTG lever be moved further towards the closed position with little force when in the LL (low-load) position? If so, the VTG rod is probably set too long (for some reason). I can't directly answer that question about the force, because I didn't disassemble the pressure vessel (and I don't want to... it's original). I can only assess it if I'm working against the spring inside the vessel, and in that case, I can't detect any difference.

You may have misunderstood something.
The can should not be lowered for the test. Instead, you should only feel your way along the VTG bar (if necessary). Break the hand and arm as many times as necessary ), and immediately after a cold start (to avoid burns), push the rod towards the can.
If she's giving in, then the rod is probably set too long (from the factory?).

Or, your engine might be a rare model where the variable geometry turbocharger (VTG) doesn't fully close at low load.
Then, the LD-TV should ideally continue to decrease, especially at high speeds and low engine RPM, otherwise, the potential for early LD buildup is being wasted .

Quote:

- furthermore - the pressure chamber is controlled with a 0% duty cycle (full vacuum), which essentially means it operates in the default mode and goes all the way to the stop.

That doesn't contradict my thoughts.

Quote:

Unfortunately, I haven't been able to test this phenomenon on another similar engine yet - but the workshop says that it's normal.

Isn't that what the average workshop (almost) always says?

You're probably right about the workshop.

I actually wanted to try again to access it from above, but I knew that would be a problem. It was already difficult with the ASV, as there was only space for a snake-like attachment. But with the ARL, it's completely impossible because there's a large aluminum intake pipe, the size of a gutter drain, blocking the way. We had previously tried to fix it from below on the lift, and even at idle, the part could be moved a little bit until it hit its limit.

Devilseye503 wrote:

but with the ARL... you could still move that part a little bit when it was idling, until it hit the stop.

Ah, an accident report.

IIRC, the ARL software normally controls the VTG (Vertical Turning Gear) in the low-speed range using the same TV (torque value) as it does during acceleration (which specific MSG are you referring to?).
So, if there was more than approximately 1 mm of free play in the VTG rod on the stage, measured from the rod to the closed position, then your car is likely losing a significant amount of potential boost pressure, especially considering that the ARL turbocharger doesn't produce a huge amount of boost to begin with.