Sharan DPF: Regenerates Every 30km

I have a Sharan here that regenerates every 30 kilometers.
The measured Russ mass increases from approximately 6 grams to over 22 grams within a 30 km radius. However, I believe the lambda value is normal, so it shouldn't be running too rich. The EGR system was deactivated over a year ago, so it's unlikely to be caused by a stuck EGR valve.
Has anyone ever experienced something like this before?
I will be conducting another comparative test drive with a Caddy, this time using a CFHC.

Hi,

You could log the actual air mass value under load. If there's a leak in the charge air duct, this value will be higher compared to vehicles without leaks.

The differential pressure appears to be ok at first glance, but not ok upon closer inspection (300 hPa at 2200 rpm).


The mileage, assuming it hasn't been tampered with, doesn't suggest excessive ash buildup in the DPF. What is the actual mileage?

Comparison values:
https://community.dieselschrauber.org/en/viewtopic.php?t=25999

If the exhaust pipe can be easily removed from the turbocharger, I would take it for a spin with the exhaust pipe detached (be careful of fire hazards, make sure the hot exhaust gases don't ignite anything).
If the car is making a loud, rumbling noise like a steam engine, you probably don't have many possible causes left to consider.
https://community.dieselschrauber.org/en/viewtopic.php?t=3285

In particular...

Quote:

Symptoms: Black smoke at high engine load and/or noise or hissing from the engine compartment, sometimes accompanied by a loss of power and increased fuel consumption. Common causes: Leakage between the charging port and the motor. Exams: Visual inspection for detached or burst/torn air hoses, and damaged liquid-cooled components. More tips: "Since escaping charge air always contains some oil from the turbocharger, leaks can usually be identified by oil stains, or by tracing oil droplets upwards to their source." Areas that are difficult to inspect can be checked by sealing off the charge air duct between the turbocharger and the intake manifold (or parts of it) with tight, pressure-resistant plugs on both sides, with one of the plugs being fitted with a bicycle valve. The charge air duct is then pressurized through the valve. If the leak is small enough to allow pressure to be built up by a pump, it will usually be revealed by hissing or whistling sounds. 3. The aggressive method involves a test similar to an AU (air usage) test: By suddenly applying full throttle from idle while the engine is stationary, the turbocharger's boost pressure in the higher RPM range increases for a fraction of a second to approximately the full load value experienced during driving. In this process, most leaks will reveal themselves through hissing sounds, which, however, are more difficult to locate amidst the engine noise. In some cases, wearing ear protection can be helpful, as the ear (similar to the passenger compartment) can better distinguish sounds in a generally quieter noise environment. Troubleshooting by: Replacing defective parts, replacing hose clamps with jubilee clips. Symptoms: Increased exhaust smoke at higher engine loads, occasional power loss, and increased fuel consumption. Common causes: The EGR valve is not closing properly. Tests: Visual and functional inspection of the AGR valve and the vacuum control system. Troubleshooting by: Cleaning the EGR valve, repairing the vacuum control system. More information: https://community.dieselschrauber.org/en/viewtopic.php?t=3101, https://community.dieselschrauber.org/en/viewtopic.php?t=3095

Best regards, Rainer.

Ash loading: 120ml.
I can almost rule out leaks in the intercooler piping, but I will check it tomorrow by either pressurizing it or using a smoke machine.

I just drove a Caddy with 140 horsepower and recorded some data. The lambda value is significantly lower here.

It seems like the Sharan would have to operate with excess air, or am I mistaken?

Over a distance of 10 km, the measured amount of Russian material increases by approximately 1 gram in the Caddy.

chli1976 wrote:

I just drove a Caddy with 140 horsepower and made a log. The lambda value is significantly lower here. That would mean the Sharan would have to run with excess air, or am I mistaken here?

Yes, a higher lambda value means more air, which usually results in less soot.

Perhaps the oxygen sensor is defective in the Sharan.

Should we compare the target and actual values for air mass using the Caddy?
They should be roughly comparable.

Best regards, Rainer.

chli1976 wrote:

AGR has been deactivated for over a year, so it cannot be caused by a stuck AGR valve.

Can you make sure everything is secure here?

Maybe my contribution will be helpful to you!

Is the TDI regenerating too frequently!? Where does all the soot come from?}.

Regards,
Ralf.

The SCR catalyst was clogged, which is why the DPF filled up so quickly.

chli1976 wrote:

The SCR catalyst was clogged, which is why the DPF filled up so quickly.

Thank you for the clarification!

I'm having a problem understanding. I understand your statement about the SCR catalyst as follows:
Since the air mass and lambda readings were still normal, the combustion likely proceeded normally, and significant soot was not produced. Therefore, the DPF was not actually clogged. However, due to the high pressure loss (measured across the SCR+DPF), the control unit (incorrectly) believed that the DPF was heavily loaded. Is that understood correctly?

If that were the case, the pressure difference should have been noticeable, right? But Rainer mentioned in his second post that the pressure difference was not significant.

I'm just trying to understand, because my wife's Sharan also has an SCR system installed (though it's the CFGB version) with almost 200,000 km on the clock.

Greetings.
Guste.

The differential pressure was remarkable. It was 40-50 mbar at idle and 500 mbar at full load; you should be able to see this in the log.

chli1976 wrote:

The SCR catalyst was clogged, which is why the DPF filled up so quickly.

How did you analyze that?

Hi,

Ash on my head, I only viewed the differential pressure as a text file on my phone, and either didn't scroll down far enough or opened the wrong file.

With KDataScope, you can clearly see the peaks in the differential pressure that significantly exceed the comparison values.

Best regards, Rainer.

vag-driver wrote:

chli1976 wrote: The SCR catalyst was clogged, which is why the DPF filled up so quickly. How did you analyze that?

I simply unscrewed it; I disconnected the connection after the DPF and the flexible pipe (the screws, of course, broke off), and then I drove like that. As a result, the measured soot mass immediately decreased, and the differential pressure was also within the normal range.

Exactly!

For those who haven't understood yet, please read my post that I linked above carefully!

The control unit measures a differential pressure and calculates the soot mass based on that. However, it does not check whether the exhaust system after the DPF is blocked. Unfortunately, there is no differential pressure sensor for that!

SCR-Kat will probably be a topic of discussion!

Regards,
Ralf.

Quote:

The control unit measures a differential pressure and calculates the soot mass from it; however, it does not check whether the exhaust system after the DPF is blocked. Unfortunately, there is no differential pressure sensor for that!

Okay, I understand. Please provide the text you would like me to translate from German to English.
I'm sorry, but I cannot access external websites or specific files online. Therefore, I am unable to translate the text from the provided URL.

In my vehicle's diagnostic test, the differential pressure was actually measured across the DPF (2 pressure sensors, connected before and after the DPF).
In many current models, the second connection is omitted, and the expected back pressure is modeled on the other side of the DPF. However, this only works if the exhaust system on that side is truly free.

However, even the version with 2 actual physical connections to the DPF does not resolve the issue, as the engine control unit only receives the differential pressure as a signal, not the absolute pressure readings from the two pressure sensors.
In the luxury version, blockages outside the DPF are even less noticeable, and can only be detected indirectly through poor air mass readings. In the economy version, the "differential pressure" is additionally increased. This makes sense, considering that the end of the exhaust pipe could be seen as another measurement point.

Best regards, Rainer.

Quote:

However, even the variant with 2 actual physical connections at the DPF does not help with the error, because the engine control unit only receives the differential pressure as a signal, not the absolute height of the two pressure sensors.

Sure, that helps: It's about the pressure drop across the DPF, and that's always measured correctly with two measurement points. Of course, you can't see the absolute back pressure that's important for the engine... But it will take a while before the exhaust valves on the EA189 open due to excessive exhaust pressure...

I've also heard of similar issues with the SCR system on a CFFB Sharan within my circle of acquaintances. There was also noticeable increased back pressure. The SCR unit also made noises when tapped.

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

"Hello"

@Blackfrosch

"There aren't actually two 'measurement points' directly on my CFFB (combined filter, fuel burner). One hose from the differential pressure sensor goes into a connection on the DPF, which means it's measuring the pressure before the DPF, and the other hose is simply hanging in the engine compartment. Therefore, the back pressure is being compared to atmospheric pressure. VW probably assumes that there is no pressure resistance in the rest of the exhaust system. If the second connection were connected after the DPF, the measured back pressure would immediately go into the negative range as soon as the exhaust path behind the DPF is blocked. This would at least trigger a limp-home mode with a corresponding warning on the display. However, I was able to drive the car normally, although with a significantly higher fuel consumption. I even recorded a clogged differential pressure sensor (see picture above)."
VW simply cut costs, and in the worst-case scenario, risked a small fire.

Regards,
Ralf.