2.5 TDI 150HP AKN: No Speed Limit?

Hi, I've been the owner of a Passat 3BG 2.5 TDI V6 150 hp (AKN engine) for a few months now.

Initially, it was running very poorly... but now I've adjusted the fuel injection pump (ESP/VP44) and checked the idle speed control. The idle speed range is within .50mg/stroke, so that looks good too.

What I've noticed is that the air mass readings from the actual value (IST) and the target value (SOLL) are deviating by as much as 200mg, even when using the original VCDS software and cable.

I cleaned the mass airflow sensor and reset the learning values. Since then, it has been fluctuating around 280 mg/H at idle, whereas it was at 510 mg/H before.

According to the GPS, the top speed (VMAX) is 183 km/h.

I have no prior knowledge of that engine, whether it's good or bad, but my 1.9 AVF engine, a 4-cylinder, reaches 223 km/h according to GPS. My 1.4L gasoline engine with 85 horsepower reaches 184 km/h according to GPS on a straight road, without a turbo... so I was expecting better performance.

You can also notice when accelerating that it sometimes feels like you need to go to the bathroom, you hold it back because you can't get there, and then when the bathroom is free, you can finally release the pressure (sorry, that's a silly example), but it "feels like that when accelerating – pressure builds up, and then around 2300 RPM, there's a sudden surge of power."

The intake manifold had already been removed and cleaned of carbon buildup, the gasket had been replaced, and you can tell from the exhaust that the back pressure is very high (you can feel it with your hand held near a cloth).

It doesn't smoke, and it starts easily.
Currently, in the diesel engine, after extensive work on the hoses and a seal replacement on the fuel sensor, no air bubbles are visible either.

The VTG rod retracts visually and extends.

The air filter is also clean.
To rule out the diesel filter as a potential source of the problem, I disconnected it and connected the hoses using a connector, but that didn't make any difference.

Ideas and suggestions would be great.

Hello,

Quote:

I cleaned the mass airflow sensor and reset the learning values, and since then, it has been fluctuating at 280mg/H at idle, which is the target value. Before that, it was at 510mg/H.

The expected air mass value is approximately 500 mg/H without exhaust gas recirculation. Whether exhaust gas recirculation is active or not can vary, for example, depending on the amount of time the engine has been idling, as indicated by data from the engine control unit in various older records.
It is important that the target and actual values can be adjusted when the engine is idling. The stated value of 510mg/H suggests that the camshaft is okay and that the valves are still opening fully (a problem found in various 2.5L V6 TDIs).

It's important for you to determine whether the engine control unit (ECU) allows the full fuel injection amount when the engine is running at full throttle (limited by torque), or whether a reduction occurs due to a lack of air mass. This can be seen in measurement block 8 from the engine control unit.

If there's a lack of air mass at full throttle (actual value is at least the target value), the cause needs to be determined. For example, it's necessary to check if the variable turbine geometry (VTG) can be adjusted, if the vacuum system is functioning correctly and is leak-free, or, unfortunately, if worn camshafts are preventing proper cylinder filling.

I would highly recommend the following article to you:
I'm sorry, but I cannot provide a translation without the text you would like me to translate. Please provide the text from the URL you mentioned, and I will be happy to translate it for you.

Best regards, Rainer.

Hi.

Is the required boost pressure being achieved?

"In V6 TDI engines, it's common for vacuum leaks to occur in various places, which can also affect the turbocharger pressure regulation."

It took me quite a while to get the full potential, roughly 180 horsepower, out of the engine in my Passat 3BG 4-Motion.

"What's a fact is that the AVF completely outperforms the AKN; I have a direct comparison between my A4 Quattro and my friend's AVF in his Passat 4-Motion."

And the AKN is a purebred 4-valve engine that requires a certain RPM to move forward; it doesn't really perform well below 2500 RPM, but above 3000 RPM, it revs like a gasoline engine.

Yesterday, I winterized my AKN engine and noticed the huge difference compared to the BDH engine during the first test run, especially how smoothly it pulls out of the low RPM range.