FSI failed on emissions

[Evripidis]

Even the simple temperature test could be an indicator. Ruled out a faulty cat in the past but that was only an open loop pre-cat lambda system.

 

[dances-with-pies]

Set VCDS to monitor bank 034 (cat temp) which showed 340 degrees at idle and then measured cat temp with an IR thermometer.
Front end of cat 112/113 degrees and the back was 118/122.

Used an assistant to bring revs up to a constant 2,500rpm which increased VCDS cat temp to 505 degrees.
Front end of cat now reading 122/124 and back showed 124/128.

Most videos imply that the temperature at the rear of the cat should be considerably higher if the cat is working correctly.

 

[Evripidis]

I was thinking about this today as I got a P0420. Could be that the lambda sensor is 170k miles old though...

Are we talking the pre-cat or the cat?

 

[dances-with-pies]

The main cat.

 

[Evripidis]

I haven't checked yet. Got caught up with other issues. I'll try and do it quickly after a short trip. My apologies.

 

[PlasticMac]

Set VCDS to monitor bank 034 (cat temp) which showed 340 degrees at idle and then measured cat temp with an IR thermometer.
Front end of cat 112/113 degrees and the back was 118/122.

Used an assistant to bring revs up to a constant 2,500rpm which increased VCDS cat temp to 505 degrees.
Front end of cat now reading 122/124 and back showed 124/128.

Most videos imply that the temperature at the rear of the cat should be considerably higher if the cat is working correctly.

I think that's because the cat is supposed to be burning the residual hydrocarbons and carbon monoxide. This requires heat from the exhaust gases to happen, and, (guessing here), produces more heat in the process. The exhaust needs to get very hot, this is not going to happen other than on a longish run.
If any of the many sensors throughout this process gives incorrect reading, the mixture will be made richer or leaner. If it is richer, then the cat will be overwhelmed, and CO at the exhaust will increase. Same result if the cat is defunct.
VCDS can show fuelling rates, but I've never gone that deep, never needed to.
I remember someone mentioning a session on a Bosch diagnostic kit, that diagnosed such a problem. Google Bosch Injection specialist, especially mobile ones.
Mac.