The DPF filter isn't leaking, but has frequent regenerations

Obrázky, fotografie a soubory

Chemical traces (17320/1)

The white liquid staining of the outer filter body indicates that the filter was cleaned on the vehicle using an ineffective and, most importantly, very dangerous method for the DPF (risk of permanent damage to the DPF). A chemical solution is sprayed through the hole before the DPF and left to act for a while. Afterwards, the engine is started, and usually, the filter is "flushed" with another chemical solution. Finally, the vehicle is taken for a test drive to warm up, enabling the dissolved deposits to evaporate. (This method is technical nonsense. The sale of this product/method should be banned.)

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So far the filter shows no signs of leaking (17320/2)

By looking into the exhaust tailpipe, we can't confirm if the filter is permanently damaged due to cracked filter ceramics. So maybe it's just a matter of time before the tailpipe becomes fouled with soot.
The chemicals usually partially clog the pores of the DPF filter, and the high exhaust back pressure damages the filter. In addition, the MIL light is ON because the exhaust gas flow has high resistance under driving conditions.

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First intial log recording – Meaningless and unrelevant values (17320/6)

A look at the first graphs revealed, besides the meaningless displayed CALCULATED value of the particulate filter saturation at 149% (this is physically impossible when the differential pressure is low), the soot volume of 0.94 g (also meaningless in relation to the percentages), the mileage between regenerations of 1,178 km (also meaningless), and the total mileage at 15,136 km (also meaningless). However, we don't know if someone has tampered with the engine ECU data.

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Log recording after registering the DPF filter replacement (17320/7)

Because the 1st Log recording showed relatively low-pressure values under all load conditions, we applied the re-learn function to the DPF filter values (as if a new DPF filter had been installed). The system soot content % count started calculating the relevant values (0 %). If the value continues to rise at a similar fast rate to here, then the particulate filter will have to be removed and cleaned from the opposite direction. We will see if the cleaning procedure is going to be successful. Our experience tells us that filters clogged by chemicals are damaged permanently.

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Simple DPF saturation adaptation linearity test (17320/8)

If, in this test, with higher exhaust flow but without load, the soot saturation rises more steeply than at lower rpm. Then there is a higher risk that the engine ECU won't be able to interpret a DPF filter "cleaned" by this method.

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More in-depth test to verify DPF compatibility with ECU software (17320/9)

Because someone cleaned the filter without disassembly, we need to check with a specific Log whether the chemicals have not remained in the pores of the DPF ceramics after drying and haven't changed the resistance characteristics of the exhaust gas flow.

1) High RPM phase at low load (driving mostly downhill at higher RPM). The shift indicator shows to shift 6th gear, but we are in 3rd gear. In this mode, the soot "buildup" calculation calculates an unwanted INCREASE. The engines don't smoke in this mode (fuel consumption shows from 1 L/100 km to 3 L/100 km). And the fact that they don't smoke is demonstrated not only by city driving (3), but also by the idling phases before, during and after the test, when the value of backpressure at idle doesn't rise dramatically.

2) Low RPM phase on the highway at medium to lower load (speed of approx. 90 to 100 km in 6th gear at 1200 to 1500 rpm). Soot saturation calculations in the filter rise too steeply. The exhaust flow is higher in this mode because the turbo is boosting (showing higher airflow), and the exhaust gas flow is also more intense. The resistance recorded by the differential pressure sensor and the measured pressure is too high.

3) In the "City" phase, with numerous starts and slower driving without longer turbo engagement, the engine is often at idling or medium RPM. The load is normal to medium. The soot saturation calculation doesn't change; it even drops at low RPM after a few idle phases at the same steep slope as it increases at higher RPM or under load. So, the idling phase implies that the filter isn't saturated, while the higher RPM and load imply it is.

The downward curve of the soot saturation calculation shows that it was calculated incorrectly in the previous stages, "higher value compared to the actual". The dashed line below shows the expected soot contamination value very approximately.

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Log recording after regeneration and learning a new DPF filter (17320/13)

The soot saturation percentage calculated after 28 km of slow driving shows 10%. The back pressure is almost the same as before regeneration—from 0 to 10 bar in several test modes during idle, which must be done while driving. When accelerating with a clean (after regeneration) and newly learned filter, the differential pressure sensor gives a value of about 180 mbar, in the extreme (4700 rpm) 220 mbar. Mercedes doesn't like this and calculates the saturation level abnormally fast.

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Todays motorway test drive (downhill and mild uphill) after cold start (17320/17)

Yesterday, it seemed that the ECU wouldn't calculate the DPF soot saturation; today, the value started to increase again, although the differential pressure is not dramatic compared to other brands. This is because the DPF body is oversized for a 1.6 CDi engine. The calculation from the pressure values probably takes into account the size of the DPF body.

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The DPF filter "cleaned" by the previous workshop (17320/19)

Cleaning on the vehicle should be forbidden under a severe penalty for the mechanic.

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After cleaning using a method provided by Advanpure (17320/22)

The chemically contaminated DPF filter was cleaned by 650 °C hot low-frequency pressure shocks in the opposite direction of the exhaust gas flow. This method removed 40 g (!!!) of contaminants out of the filter and the differential backpressure at idle dropped from 11 mbar to 2 mbar. The test drive with a Log recording confirmed that the filter is now largely cleaned, and if it wasn't for the damage caused by the previous incorrect procedure, it could have continued to work on the car without any fault code activating.

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Photo from the rear side after the flter was cleaned (17320/23)

The chemicals have been removed from the filter, but there are cases where thorough cleaning is impossible.

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After cleaning by ADVANPURE – gradually increasing DPF filter saturation (17320/25)

Currently, the car can travel 500 km between regenerations.

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Log recording after thorough cleaning with ADVANPURE procedure (17320/27)

290 km = 2.7 g = 47% soot saturation (before regeneration)
The controller algorithm calculates the saturation gradually without jumping up or down.