Check Golf 4 VR 5 AGZ catalytic converter, engine running rough.

Hello, we have a Golf 4 VR5 here. When it's stationary, it runs like a tractor. We've already replaced the spark plugs (they all looked fine!), the ignition module, and the ignition coil, but without success. The error memory keeps showing a fault with the oxygen sensor. Now we suspect a clogged catalytic converter, as there was a loud bang from the exhaust system during a highway drive, accompanied by a cloud of black smoke and a noticeable increase in power from that moment on. What should the back pressure be before the catalytic converter?

Hi,

Quote:

What should the exhaust back pressure be before the catalytic converter?

It's relatively low because the CAT isn't like a closed DPF; it's simply a bundle of tubes through which the exhaust gases flow.

The exhaust back pressure will be somewhere in the upper double-digit or low triple-digit mbar range.

"Misfires" or "pops" coming from the exhaust system can occur with an overly lean fuel mixture.
Therefore, I would focus on adjusting the lambda parameters.
Okay, I'm ready. Please provide the German text you want me to translate.

Please also post the excerpt from the Autoscan, including the error memory dump.

Best regards, Rainer.

Hello,
I also have a V5 with an AGZ engine. Mine has an automatic transmission.
Problem areas are likely to be...

Throttle valve:
While the AGZ unit includes a Bowden cable, it still has a potentiometer. The problem is that there's another spring underneath the existing spring, which prevents the throttle valve from returning properly to the zero position. A little spray lubricant and recalibration should do the trick.

Power amplifier module:
When you're standing in front of the engine, on the right side of the splash guard, you'll find this part with an aluminum base and two connectors. Inside, a connection comes loose, and then it only runs on 4 cylinders.

Ignition module and spark plug wires (do you already have these)?
The ignition module was also broken in my car, but I see that you've already replaced it. You can quickly locate sparks that are jumping with a spray bottle of water.

Not great: Timing chain.
Due to a defect in the oil pump (mainly due to contamination), the timing chain stretches. This can shift the valve timing to such an extreme extent that the engine runs unevenly. This repair is extremely complex because both timing chains are located on the transmission side, and it's best to replace the oil pump at the same time.

It's possible that the power amplifier module is broken. In such cases, misfires or problems with the ignition system often also lead to damage to the catalytic converter.

Good luck.