Is it normal for these to overfuel when you put you foot to the floor - around 4000rpm if you have the windows open it stinks.

I get no faults or anything just the stink.

The car since I’ve had it has done this but also since I’ve had it it’s had a cheap cat on one bank. I’ve got a new one to fit this month as in my head this was the cure but my buddy reckons if it’s overfuelling it will still be stinking from the genuine cat.

Any ideas? Do they just do this? Current stable:
2006 BMW M6
2007 4.2 V8 S/C FF
Gone:
2002 4.4 V8 FF

Whip the engine cover off too see if there's any obvious leaks would be a good start and see if you can get a garage too check the fuel pressure and see where it leads you too mate

Engine cover is always off got sick of the the Matt disintegrating - no obvious leaks I can get a smoke test but done this before and nothing obvious.

I do have an original iid tool can I check on there? What should I be seeing? Current stable:
2006 BMW M6
2007 4.2 V8 S/C FF
Gone:
2002 4.4 V8 FF