Can you explain just how the engine runs lean with decats. and by how much, AFR etc, as air fuel is determined by incoming airflow,and lambda feedback, so anything that increases/decreases this will be compensated for by lambda feedback,
so in order for the ECU not to be able to compensate AFRs would need to be way out of range which decats alone would not do, if this was the case a lot of Z would be in a bad state.
When i took it to Abbey, and had a run as it was before the map, i asked Mark if it was running rich or lean, and iirc, i remember being surprised when he said "lean", which was the opposite of what i thought. I may have remembered that wrong. If you think it's wrong, then just disregard what i said, but i was basing it from that memory, not from my mechanical know-how.