Golf 4 VR 5 AGZ Catalytic Converter inspection, Engine not running smoothly.

Hello, we have a Golf 4 VR5. When stationary, it runs like a tractor. We have replaced the spark plugs (they all looked the same!), the ignition module, and the ignition coil. But without success. The error memory always indicates a faulty lambda sensor. Now, we suspect a clogged catalytic converter, as there was a bang from the exhaust system during a highway trip, along with a cloud of smoke and more power from that moment on. What should the exhaust backpressure before the cat be?

[Translating...]

Hi,

Quote:

Wie hoch muss der Abgasgegendruck vor Kat sein?

ziemlich niedrig, denn der KAT ist nicht wie ein geschlossener DPF ein Filter, sondern einfach nur ein Röhrchenpaket, durch das die Abgase strömen.

Der Abgasgegendruck wird im irgendwo im oberen zweistelligen oder niedrigem dreistelligen mbar-Bereich liegen.

"Fehlzündungen" bzw. "Knall" aus dem Abgastrakt gibt es bei zu magerem Gemisch.
Von daher würde ich mir die Lambda-Anpassungswerte vornehmen:
/viewtopic.php?t=21836

Poste doch bitte noch den Ausschnitt aus dem Autoscan, mit dem Fehlerspeicherauszug.

Viele Grüße, Rainer

Hello,
I also have a V5 with an AGZ engine. Mine is automatic.
Problem areas are likely...

Throttle:
Although the AGZ has a Bowden cable, it still has a potentiometer (pot). The problem is that there is another spring underneath the springs, and the throttle valve no longer goes to the correct NULL position. That helps with some spray oil and re-tuning.

Final Module:
When you're standing in front of the engine, to the right of the splash guard, there's this part with aluminum flooring and two connections. Inside, a connection is lost, and then he only uses 4 burners.

Ignition module and ignition cable (have you already):
The ignition module was also faulty with me. But you already replaced it. With a spray bottle filled with water, you can quickly find sparks that jump.

Not so great: Chain of taxes
Due to a defect in the oil pump (primarily due to contamination), the chain becomes stretched. This can shift the timing so significantly that the engine may run unevenly. This repair is extremely complex, as both timing chains are located on the gearbox side, and it would be best to also replace the oil pump at the same time.

It is possible that the final stage module is faulty. This often leads to issues with the catalytic converter (KAT).

Good luck