TDI Turbocharger: Boost for Dirty Air Filters?

Hello,

As is well known, the speed of the turbocharger increases with the pressure ratio between the compressor outlet and inlet, as well as with the (intake) volumetric flow rate.

If the turbocharger is required to deliver the same absolute boost pressure at all times, even at low intake pressures (e.g., at high altitudes), then it must spin faster as the altitude increases.
To prevent it from breaking down due to excessive speed, there is a "height protection characteristic" that limits the maximum desired load torque based on the ambient pressure.

The ambient pressure is measured by a sensor in the engine control unit (ECU) and does not have to be identical to the pressure at the inlet of the supercharger. On the intake path to the supercharger (including the intake snorkel, air filter, and mass airflow sensor), some pressure is always lost depending on the volume flow, which means that the pressure at the supercharger is different from what the ECU expects. To prevent the supercharger from over-revving, the manufacturer can naturally incorporate appropriate safety margins into the altitude compensation map.

The difference between the intake manifold pressure and the boost pressure becomes particularly significant when the air filter is heavily soiled. In such cases, the turbocharger may have to work considerably harder than what the engine control unit (ECU) calculates, and in extreme cases, it can even fail without any modifications.
However, for a heavily clogged air filter within the normal replacement intervals, there should be some reserve capacity in the altitude correction map that could potentially be exploited through chip tuning, provided the driver always ensures the air filter is clean.

My question is now:
Does anyone know what Pmax pressure drop range the VAG developers approximately expect between a new and a worst-case, worn-out air filter housing for the TDIs?

Hi Ulf,

Without being able to give a specific answer right now, but perhaps still interesting: In some software versions, the error thresholds for partial load seem to be set very narrowly, causing the control unit to force the customer to take the vehicle to a workshop with a "Boost pressure differential - regulation limit exceeded" error message when there is a clogged air filter. This occurs in the lower and middle partial load range, with a cold engine.

However, this only occurs in some software versions, and not in all vehicles, which is why I believe that component tolerances play a significant role.

The error often occurs with a clogged EGR valve, because in that case, the intake volume is actually forced through the air filter, which increases the pressure difference.

Quote:

The error often occurs with a clogged EGR valve, because in that case, the intake volume actually has to pass through the air filter, which increases the differential pressure.

I'm sorry for rambling on like this! But could this be the cause of the protest from my 1.4 HDI engine against the closing of the fuel line to the magnetic valve for the EGR control?

"Using the modifications recommended by vwSchrauber, I was able to drive without errors on country roads and in city traffic. However, even in the interesting speed range on the highway, a fault code still appears with the yellow MIL (Malfunction Indicator Lamp). The error code reads: "Mass airflow sensor value implausible, intermittent." Furthermore, the error can be triggered by accelerating with more than half throttle. On the highway, it occurs with a very light touch on the accelerator pedal at speeds of 115-125 km/h. If you suddenly accelerate hard at 90 km/h, you can also trigger the MIL."

Since I was driving with the retrofitted LLK (low-temperature coolant system) until late autumn, I repeated the test now without it. I don't need it in winter temperatures, and the smaller volume of air that needs to be compressed in the intake manifold results in a more responsive engine. The result was that the MIL (malfunction indicator lamp) came on under the conditions described above, but now it turns on even at highway speeds with very light acceleration, around 105-110 km/h. When accelerating more quickly or pressing the gas pedal more, for example, when overtaking, it turns on immediately.

I first blew out my used air filter "backwards" with compressed air and reinstalled it. Afterwards, I temporarily replaced it with a new filter, but it made no difference. Since, in my opinion, the installed filter wasn't yet ready to be replaced, I blew it out again and reinstalled it. It should be fine for the remaining kilometers until the 90,000 km service.

Well, I find that quite interesting...

When the AGR (Abgasrückführung) valve is closed, the air/intake volume must pass through the air filter and the turbocharger. Consequently, the exhaust gas flow rate increases, and the turbocharger receives more torque, which in turn results in an increase in the amount of air being drawn in through the air filter.

It's inexplicable that in your case, the fault is only detected when the load increases, or when a threshold is exceeded. This is because the AGR (Abgasrückführung - exhaust gas recirculation) should be active at the latest from 16 mg per cycle – at least, according to the software version I'm familiar with. Your ECU (Engine Control Unit) number would be interesting to see if it's the same one (the one with the 0 281...).

Regarding airflow resistance, a K&N fabric filter might offer slight advantages, as long as it's not excessively oiled (be careful of the mass airflow sensor).

Quote:

K&N fabric filters have some advantages

.

In the early days of this forum, Rainer proved the opposite .

m;

@vwschrauber
"I've been experiencing the phenomenon you described in my 1.4 TDI AMF for some time. The emissions exceed the limit only under low load and with a cold engine. It first appeared after the turbocharger boost pipe burst. I've since fixed the leak, but the sporadic error still occurs."

So, I should check the oil level sometime?
It wasn't that old, at least not for my standards... definitely not yet 100,000 km...
Let's see if it makes a difference...

P.S.
I replaced the air filter. It didn't make a difference.

The problem still persists for me.

Otherwise, it's worth mentioning that the car has an aftermarket DPF (Diesel Particulate Filter). However, it was installed shortly before the problem occurred.

The issue has worsened to the point where I can now sometimes reproduce the error even with a warm engine (always at slightly over 2000 RPM and during prolonged periods of partial load).

Given this, I had already dismissed the idea that there might be air in the fuel return line due to worn-out solenoid valves (PD elements). So far, I haven't bypassed the "knack frog" (presumably a fuel filter or similar component) to ensure that fresh fuel is always drawn from the tank, even during the warm-up phase.

No charging pressure leaks are visible. The turbocharger spins freely and exhibits no excessive shaft play.

Besides that, I suspect the wastegate might not be closing completely, as I feel the boost pressure comes on a bit later than before, even with a warm engine. However, there are no significant overboosts.
Unfortunately, it's not easy to check without messing around with the rusty screws on the exhaust manifold.

The engine has a chip installed that operates very close to the smoke limit, and it's slightly more prone to entering limp mode due to technical defects than with the standard software. However, I've always had this chip installed.

Do you have any other ideas? Or should I just try bridging the gap anyway? I haven't done that before because I haven't had a suitable fuel hose on hand.

"Thank you!"

P.S.
The engine has clearly exceeded 200,000 kilometers, and almost all of that mileage was driven with a performance chip installed.

Quote:

Almost everything there is with a chip.

What are you making such a fuss about? It's probably just that someone watered the LD-Soll with a watering can again, and the target charging pressure is simply defined as too high for certain operating points.

Best regards, Rainer.

Well, the thing usually works without any problems, right?

Actually, there is no noticeable increase in boost pressure according to the manufacturer's specifications. Only the amount of fuel injected is being increased, up to the point where smoke appears (at least under full load).

Even if you are right:
So, something must have changed that is now causing the problem.

Olaf wrote:

Well, the thing usually worked without any problems, right? "According to the manufacturer's specifications, there is actually no noticeable increase in boost pressure. Only the fuel injection quantity has been increased up to the point where smoke appears (at least under full load)." Even if you are right: Therefore, something must have changed, which is now leading to the problem.

The turbocharger is slowly failing... If you log the MWB 11 value and gradually press the accelerator pedal (always for at least 3 seconds each time, to allow the turbocharger speed to adjust) from zero to partial load, you might see a target boost pressure of 1600 mbar, but an actual pressure of 1295 mbar... then you'll hear a "plop" and that's it.

Best regards, Rainer.

OK, thank you.
I thought so. But the wave looked so healthy, I wasn't sure. Also, no oil is leaking through.

Well, I still have a spare charger lying around...

Quote:

If you log MWB 11 and gradually press the accelerator pedal (always for at least 3 seconds, so that the turbocharger speed can adjust) from nothing to partial load, you might see a target boost pressure of 1600 mbar, an actual pressure of 1295 mbar... then a "plop" sound, and that's it.

Olaf wrote:

OK, thank you. I thought so. But the wave looked so healthy, I wasn't sure. There's also no oil leaking. Well, I still have a spare charger lying around...

That might not be helpful to you either, in the scenario that Rainer described.

I can only recommend creating a log in the manner described and actively looking for significant discrepancies between the desired and actual values.

That probably takes less time (15 minutes) than changing the charger and struggling to figure it out.

Sure, the boost pressure fluctuations are already present, as you described. I had already checked that using VAG-COM before.
Just to avoid any misunderstandings:
The boost pressure definitely builds up later than it should, and at partial load, around 2100 RPM, it's not as present as it should be, regardless of the target value set in the engine control unit (ECU).

The question was simply about the cause, whether it was actually the charger or something else.
because the wave is not only described by me but also by the workshop as being OK, running smoothly, and with normal play.
I just haven't taken anything apart on the wastegate side yet.

I have another pressing question where you might need to use your crystal ball.

Unfortunately, I had the timing belt replaced 10,000 km ago (including the belt, tensioner, and idler pulley). The 2000 AMF model still has a 60,000 km interval. I typically drive about 70,000 km on a single belt (mostly long distances). So far, I've replaced the water pump every other time I change the belt. Once, I also proactively replaced the vibration damper.
Mileage: 210,000 km.

I recently heard from someone that, in their case, the bolt holding the tensioner pulley broke at 250,000 miles on the same engine. The part costs 75 cents including tax.

http://www.lupotreff.de/forum/t/20182

(with photos)

You can constantly swap things around, but ultimately, the real problem lies somewhere else entirely.

What should I do?

I still have approximately 50,000-60,000 km until the next timing belt replacement. Then, the water pump would need to be replaced again anyway.

I will travel those kilometers in less than 1 1/2 years.

Considering the value of the engine, what is your inclination?

"Are you familiar with this issue? VW is being uncooperative. Does this happen frequently with water pump failures that aren't directly caused by the water pump itself or the belt?"