WIV: Unforeseen Consequences and Impacts

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

"Hi,"

After my AXR has been making a terrible smoking noise when starting for a week, and I discovered a clogged ! air filter while troubleshooting, I'm seriously starting to think about the durability of an air filter.
My car now has 36,000 km on it with the original air filter still in place. At 16,500 km, a VAG dealer performed an oil change (without changing the air filter), and again at 29,000 km (due to a head gasket replacement). If the service interval had been reset each time, I would theoretically be able to drive until around 79,000 km with the original air filter. The question is, would it still be effective by then?

By the way, yesterday, for once , the AXR stopped working – no error codes stored! – The relay for power supply had bad solder joints.
Somehow, I can't shake the feeling of a Monday morning, but perhaps the lawyers should deal with that now.

That's not a WIV problem!

For my 1996 AFN model, the air filter replacement is only required after 60,000 km!

Regards,

Manuel.

Hello Bertil,

"For my A3, the replacement is also only required after 60,000 km. It's complete nonsense; if I'm driving in a cleanroom environment, I might as well not even bother with an air filter."
Every 15,000 km during the regular service, I verschandeln the air filter housing and tap out any debris like leaves, sand, or insects from the filter. After 30,000 km, I replace the air filter.
While I no longer drive on dusty roads, this thing would still be completely worn out at 45,000 km.

Best regards, Rainer.

For my AWX, the change is only scheduled for 90,000 km. I think that's quite a lot, especially since the filters get very dirty. Changing them more frequently saves fuel and soot!

'In my Golf 4, the filter was already full and black after only 10,000 km. Regarding the lifespan of the mass airflow sensor (MAF), it's definitely recommended to replace it more frequently in this case.'

Bertil wrote:

After my AXR has been making a terrible smoking noise when starting for a week, and I discovered a clogged (!) air filter while troubleshooting, I'm seriously starting to think about the durability of an air filter...

Hi Bertil,

It surprises me quite a bit that a Euro4 car (when starting) can produce soot at all, instead of the mass airflow sensor (MAF) restricting the fuel injection to such an extent that every single puff of smoke is eliminated.
Then, at least, a clogged air filter would be identifiable by the sluggish acceleration from a standstill .

Have you noticed any loss of power?

If you then imagine that the turbocharger has to increase the pressure behind the air filter from "half vacuum" back to the desired boost pressure by increasing its speed, then the altitude compensator designed to protect the turbocharger seems like a bad joke.
Above a certain ambient pressure (e.g., in high mountains), the boost pressure is reduced, but if the air behind the air filter is still much thinner, the engine control unit doesn't detect this and continues to drive the turbocharger beyond its maximum speed.

Hi Ulf,

ulf wrote:

It surprises me quite a bit that a Euro4 car (when starting) can produce soot at all, instead of the mass airflow sensor restricting the fuel injection to such an extent that every speck of smoke is eliminated.

That surprises me too!
In the workshop, the master mechanic (who seemed annoyed by my late arrival) said, "... that's normal." However, during the test drive, he readily admitted, "... definitely too much," and scheduled an appointment (which never happened).

Quote:

Then, at least, a clogged air filter would be identifiable by the sluggish acceleration from a standstill . Have you noticed any loss of power?

The "turbocharger hole" seemed a bit larger to me.

Quote:

If you then imagine that the turbocharger has to increase the pressure behind the air filter from "half vacuum" back to the desired boost pressure by increasing its speed, then the altitude compensator designed to protect the turbocharger seems like a bad joke. Starting at a certain ambient pressure (e.g., in high mountains), the boost pressure is reduced, but if the air behind the air filter is still much thinner, the engine computer doesn't detect this and continues to drive the turbocharger beyond its maximum speed . . .

Now that you mention it, I've noticed a slight puffing sound for 1-2 seconds after releasing the accelerator pedal, which seems to have disappeared now that I've replaced the air filter.

By the way, I got another K&N filter and I'm going to do some experiments with it.

Hi,

This weekend, I experimented a bit with the air filters. The AXR (and probably others as well) are quite sensitive in that regard.
The old paper filter caused a cloud of black smoke when starting the engine. The new paper filter and the K&N filter did not. According to VAG COM, the air mass was almost identical for all three filters! This is confusing me. Also, experiments where I covered part of the new filter with a plastic bag to reduce the filtering area resulted in significant clouds of smoke even when only about 10% of the filter was covered. Again, the air mass did not change significantly.
The airflow decreased significantly and the engine lost a considerable amount of power only when the filter was covered by 40%. However, the soot emissions decreased in this situation (compared to the old paper filters). It appears that the engine control unit reduced the fuel injection量.

Could it be that the mass airflow sensor (especially in the lower RPM range) is providing inaccurate readings? Or are there other correction measures available?
"In his experimental series, Rainer was able to identify clear differences between the air filters. I'll probably need to look for any irregularities in my intake system and also try a different mass airflow sensor."

I have also observed other PD TDIs exhibiting this behavior during startup. There are quite a few relatively new PD TDI vehicles (TDI or TDI) that produce a puff of smoke when starting, while others do not. Could the PD be so sensitive to external factors? In my 1Z, it wasn't as pronounced.

Okay, here's a silly question for you:
Can I tell from the outside if a standard paper filter is clogged or not? Mine has been in for about 30,000 km now, and I tap it out about once a month. In my opinion, the external condition hasn't changed much lately. While you can clearly see the dark gray areas, the filter looked like that after just a few weeks.
'Even blowing it out with the compressor (from the back!) doesn't create dust...'

Hello Bertil,

Bertil wrote:

...Rainer was able to identify very clear differences between the air filters in his series of experiments. I will probably look for irregularities in my intake system and also try a different mass airflow sensor (MAF)...

Well, the differences weren't that big. The air filter had also been in there for quite some time. I deliberately didn't use a freshly cleaned one because, in reality, you don't verschandeln it every 1000 kilometers.

Measurement at 1197 min^-1

Used paper air filter in mg/R	New paper air filter in mg/R	Fabric filter in mg/R
496	490	489

Regards, Rainer

Hello everyone,

I can't quite shake the feeling that the HLMM (High-Level Model) values things more than it measures, and that the tolerances are quite large. See also my assumption in the LMM simulator thread about why one shouldn't perform a "check calculation" using engine speed, boost pressure, air pressure, and air temperature.

Apparently, the accuracy and resolution are not very good.

Has anyone ever tried experimenting with a laser micrometers (LMM), a multimeter, and a reasonably good adjustable fan?

Best regards,

January.

Hi,

DocSnydor wrote:

Just a silly question for the meantime: Can I tell from the outside of a standard paper filter whether it is clogged or not?

"I removed a lot of willow catkins, leaves, pine needles, and tons of insects. And not even a trace of the yellow color remained. The filter was completely black throughout (even from the back)."
It is not possible to accurately determine the degree of protection.

@Rainer
The variation I observed was within the range of +/- 1mg, regardless of the air filter used.

Jan6K wrote:

I can't shake the feeling that the HLMM values things more than it measures, and that the tolerances are quite large. ... It seems that the accuracy and resolution are not very good.

I'm starting to suspect that too!

Well, then the gas stations would have serious problems.

because the HFM5 is the same for both.


I can imagine the following:

If I want to accelerate the diesel engine now, I MUST increase the fuel injection amount. Air mass is irrelevant in this case. Since the turbocharger pressure build-up always lags behind, I have no other choice but to enrich the mixture. Of course, the 'mixture' then needs to be reduced again afterwards.

The added filter creates a certain amount of resistance for the airflow. Therefore, it's conceivable that the mass flow initially lags behind, and then the boost pressure control system has to adjust everything. However, as long as the engine is smoking, especially when going from idle to full load (where the engine essentially runs as an naturally aspirated engine at first), this can happen.

If the filter is permeable, the amount of soot produced decreases because the pressure buildup (or, up to that point, the suction force) is easier to manage.

and how little diesel it takes to create a proper cloud, I think everyone here knows that .

Here's something else for the 'mushroom growers.' The HFM is sensitive to turbulence. This component is aerodynamically optimized using a laser interferometer and then placed in a 'wind tunnel' like an F1 racing car. The grid in front of the HFM is essential, as are the defined pipe lengths and cross-sections before and after the HFM.
Since it measures the air mass using a side-stream method, an incoming swirl from an open air filter would be disastrous, especially for gasoline engines with their mandatory lambda ratio. Furthermore, it compromises the backflow detection, which can negatively affect gasoline engines in particular.
The accuracy is specified as approximately 2%, although a fattening of up to 7% can be observed with very humid intake air. (which, of course, again sparked speculation about the measurement method ).

CU Gremlin.

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

"Hi,"

Gremlin wrote:

... something else for the "mushroom growers". ...

If that's what you were hoping for, I have to disappoint you.
I wouldn't even put something as awful as an open filter or one of those "mushroom" filters in my rally car, let alone in my TDI!
K&N filters are also available as replacement filters in the standard air filter size. I have these filters in all my cars. The reason for this is onlythe reusability. Because I drive a lot through wooded areas (pollen, leaves, insects...), and as a special bonus, I pass by a gravel pit (dust) twice every day, the air filter gets clogged extremely quickly. Based on the amount of dirt it collects, I would have to replace the air filter three to four times a year. That is too expensive for me in the long run. Therefore, I decided on the cotton filter (not foam!).

Your explanation about "cold start soot" sounds good, but why is this effect so extreme in my AXR (PD) engine, while the 1Z (VEP) doesn't exhibit it as much? The cloud of smoke that my AXR leaves behind during initial startup (with the old filter) is significantly denser (easily visible even during the day) compared to the cloud from my 1Z (barely noticeable). Considering the soot-free operation, the AXR engine, being an EU4 standard, should be far superior to the 1Z, which is an EU2 standard.

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

'Hi,'

Especially regarding the absence of soot emissions, the AXR engine, as a EU4 motor, should be significantly superior to the 1Z engine, which is an EU2 motor.

Basically, yes, but... the MVEG test only covers a range up to about 20 mg. Within that range, the engine is tuned for extremely low soot emissions. Since terms like 'rough start' or 'turbo lag' don't exist in the greater WOB area, outside of the EU4 regulations, the engine is aggressively optimized for starting torque. As you described, this has certain consequences. Why doesn't the 1Z do that? It was about 250 kg lighter than the AXR variant and therefore not pushed to its limits at full load.
The smoke should be particularly strong when the engine speed is lower than the idle speed (during startup), and slightly less when starting at an engine speed of 1200 rpm. Can you confirm this?

Regards,
Ole.

Your explanation regarding 'cold start emissions' sounds good, but why does this effect occur so extremely in my AXR (PD) engine, while the 1Z (VEP) engine doesn't exhibit it to the same extent?

My first thought about this was:

PD operates with higher boost pressure and almost double the fuel injection pressure, resulting in a potentially larger fuel injection volume.

The engine's fuel injection system *might* (I need to check) have such a low injection pressure within this speed range that, combined with the large amount of fuel being injected, it negatively affects atomization.

'So, we really need to log the actual injection amounts of the small 1Z engine and the larger AXR engine. I bet the AXR injects significantly more diesel than the 1Z.'


CU Gremlin.

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

"Hi,"

Gremlin wrote:

PD is running with increased boost pressure...

My car, at least, has almost the same boost pressure as my 1Z (it just has a VTG turbocharger). If it had a high base boost pressure, it shouldn't be producing soot.

Quote:

...and almost double the injection pressure = a larger possible injection volume. The engine's fuel injection system *might* (I need to check) have such a low injection pressure within this speed range that, combined with the large amount of fuel being injected, it results in poor atomization.

The injection pressure of the PD system is extremely dependent on engine speed, and it's possible that the injection pressure from idle is lower in the PD system compared to the VP37 engine. This can result in very poor atomization (even significantly worse than with the VP37), which should be the reason for the black smoke during startup.
What surprised me was the sensitivity to the degree of dirtiness of the air filter.

Quote:

"So, we really need to log the actual injection amounts of the small 1Z engine and the larger AXR engine. I bet the AXR injects significantly more diesel than the 1Z."

I'll do that when I have more time. Unfortunately, I don't have a 1Z available right now, but that shouldn't be a problem otherwise.

"...from the small 1Z to the hefty AXR..."
The AXR isn't that much more powerful than the 1Z: 90 hp / 202 Nm of torque for the 1Z versus 100 hp / 240 Nm of torque for the AXR.