Really sorry to read of your issues... If found to be the cat, and replacing with a straight through, I wonder if it could be possible to put in a parallel jumper in to provide the reading from the good cat to the ECU, to create fuelling solutions for the side with the issue.... Yeah for sure I have no idea what I`m typing about when it comes to EFI..
As for determining if any one cylinder has an issue with the engine cold then fired up, if possible you could quickly try to check the temps of each outlet point into the exhaust manifold before heat soak has an opportunity to mask the issue..? With no temp available, spit on your fingers and quickly dab on each outlet.. (-:
Wishing you the very best of luck in resolving your issue. Having recently read of a non-Morgan that would start misfiring when only when hitting a point in the rev range after which it threw up fault codes and went into some sort of limp mode.... Apparently the fault was thought to be caused by an after market air con, water-pump, alternator drive belt...Go figure as our cousins across the water might say..?
