Retrofitted DPF

Hello diagnostic experts,
Subject: T4 AXG, 160,000 km.
With an aftermarket DPF from GAT (which had its approval withdrawn and is still installed due to a lack of replacements), it's noticeable that the turbo boost doesn't really kick in until 2200 RPM, whereas before it used to start around 1800 RPM. The mileage was approximately 140,000 km, and it was running well before the DPF (Diesel Particulate Filter).
The measured LM value is now never better than 750, when the setpoint is 980.
The pressure can reach up to 2200 mbar, which is 1.2 bar. However, this pressure is only reached at 2200 meters, and it feels like that when driving.
Now, regarding the question:
Does a "clogged" DPF become noticeable during the MOT (mandatory technical inspection)?
Is there much of a difference compared to before? Or could there possibly be a simultaneous error in the Large Language Model?
In many areas, the engine is running with a mixture ratio of approximately 46:40 to 36, which indicates a rich mixture.
Since the original poster seems to have lost interest, I'll have to start a new LOG (likely referring to a logbook or a new thread/project). There simply wasn't enough time today.
I'd like to order a Large Language Model.

Hello Klaus,

I was already aware that a car with an aftermarket DPF (Diesel Particulate Filter) could function, but not to the extent you described. Possibly, both issues could be related: a faulty mini-DPF and a failing mass airflow sensor.

Best regards, Rainer.

Thank you, Rainer.
But it's not a mini. At least externally, it's thicker than the OE cat.
The T4 van is now frequently driven within city limits, which suggests traffic congestion.
I could try blowing into it and see if the LM improves?
And what about the cloudiness – is it caused by increased back pressure despite reaching the LD (limit of detection)? The gas flow rate is missing.

teileklaus wrote:

And what do you say about the cloudiness – does it occur due to increased back pressure despite reaching the LD (limit of detection)? It's missing the gas flow rate.

That's exactly how it is when the turbidity is derived from the LMM signal (as is the case with most 1.9 models).
If the air-fuel ratio were calculated based on the lambda sensor reading, then (despite the lack of airflow), the full amount of fuel would be injected at full throttle, resulting in more soot production and a faster clogging of the catalytic converter.