Engine knocking, 140hp 2.0 TDI with DPF (BMM)

Hello to all the diesel experts here!

First of all, here's the story about my 2009 Touran with a 140hp 2.0 TDI engine and DPF (BMM). SPOILER: It's going to be a long one! Sorry!

A few years ago, I suddenly experienced a jerky feeling while driving. My then-mechanic diagnosed a worn camshaft. After spending 1300 EUR, it was running again. Four weeks later, I broke down on the highway with engine damage. There was a large hole in the piston, and the camshaft was worn again. The mechanic suddenly claimed to have nothing to do with the damage. I couldn't afford a lawyer, so I just had to accept the situation.
I then bought an engine from a seller online, supposedly with 66,000 km. I had it installed at a different workshop. However, they couldn't get the engine running and they lied to me about it, claiming that the engine would work perfectly, etc. It was only the third workshop, which I still use today, that found the problem, and the engine finally started working. Unfortunately, it turned out that the engine actually had around 366,000 km, not the promised mileage. Unfortunately, the seller had already gone back to Poland and was unreachable.

Last fall, I decided to fix the leaks on the engine, specifically by replacing the oil pan gasket, head gasket, and valve cover gasket. We had planned one weekend for the job. After removing the oil pan, I found a piece of a piston ring in the oil intake screen. That was a complete disaster! Furthermore, the block wasn't a BMM, but a BMP, which means it had the unfortunate oil pump with the hexagonal shape.

Due to the issue with the piston ring, we decided to completely disassemble the engine. While all the piston rings were complete, the cylinder walls showed significant signs of wear.
Don't ask me why, but I decided to have the engine rebuilt by a specialist. The block and cylinder head were overhauled, the injectors were sent in for cleaning and repair, a new camshaft and crankshaft were polished, new bearings were installed, new oversized pistons were fitted, and new valves were installed. The intake manifold is new, the DPF (Diesel Particulate Filter) is new, the EGR (Exhaust Gas Recirculation) valve is new, the injector bridge is from 07 Eins, the turbocharger is new, the auxiliary heater is new, etc. Five weeks later, the car came off the lift. The cost of the parts with the new suspension was a whopping 8,000 EUR. The labor costs were offset in the following year by my work there. The engine runs perfectly. Fuel consumption is good, and there is no oil consumption.

The only thing that bothers me personally is that the engine has been making a relatively loud knocking noise since it was rebuilt. Does anyone have any ideas about what might be causing it, and more importantly, how to fix it? I got a VCDS yesterday.

Greetings.
Sascha.

Hello Sascha,

Is the engine control unit's fault memory empty?

Besides mechanical causes for the knocking sound, I would suggest first ruling out the "minor" things that could be causing it.

First and foremost, it's the coolant temperature. The EDC16 primarily controls the injection timing based on the coolant temperature. The injection timing significantly affects the noise level.

So, if your engine's temperature sensor is giving you incorrect readings (too low), or if the engine's thermostat is faulty (and the engine isn't actually warming up), you've already found the cause.

You can find the coolant temperature directly in the measurement data of the engine control unit.

If you have the opportunity to create a mobile video (that can be uploaded here) where the sound of the engine can be clearly heard, please do so.

Best regards, Rainer.