Audi Repair Questions? Ask a Mechanic for Answers ASAP
The first thing I would ask is have you ever had the Spark Plugs replaced? I know it may sound starnge but if these havn't been replaced they may have been deteriorating for some time and thereofre it wouldn't be unusual to see multiple misfires.
If these have been replaced and are all ok then I would suggest that the coil pack would require checking. From memory it is one coil pack on these for all 6 cylinders and HT leads off it using the wasted spark principle. I would suggest that either the coil pack or the HT leads could be your problem.
Hope this helps
Has this only happened since you replaced these items? If it has I would suggest you recheck these items for damage (i.e. are plug gaps right / no arcing up side of plug etc).
If these check out ok then you have to be looking at Coil Pack / Engine Control Module Issues (i.e. is the coild pack performing as it should, is the Control Module sending the right signal.
You night be able to check the coil pack by measuring resistance across each pair of HV Terminals.
It strikes me then that Cylinder 4, 5 and 6 aren't firing at all hence the wet plugs and the heat in the exhaust is causing the popping noise.
I would start with the Coil Pack. Maybe install the HT lead checker such as these https://www.ebay.co.uk/itm/Spark-Plug-Tester-HT-Lead-Ignition-Test-Tool-Checker-4-PACK/121621717971?hash=item1c513823d3:g:oMoAAOSwp-RahI3l
They will flash each time a spark is present. If it doesn't flash then you know you have lost the HT Voltage. This would suggest the Coil Pack is faulty.
A Catalytic Converter doesn't usually prevent the vehicle from starting unless it is totally blocked! Before spending money on this drop the downpipes off the manifold and see if it starts!
If it starts then potentially it has got a blocked CAT. If it still doesn't start then it is probably ok and would have to look elsewhere. Are you getting a spark at each plug now?
If it starts and runs for 4 minutes I would suspect that potentially it is something that is getting hot and breaking down causing it to cut out. Maybe fuel pump or something like that.
Does the vehicle restart straight away or do you have to wait a while before it will restart?
I don't think it will be the CAT as if they are blocked it will be a constant thing. I wouldn't think heat will affect it causing it block up.
That sounds like a good place to start.
If you require any further advice after this then let me know.