came into us via 3 other garages, showing missfire cylinder 1 and cat damaging misfire cylinder 1
It will only misfire after it is hot and done around 10 - 15 miles, then the miss will continue ( ecu cutting out injector ? )and only ever on cylinder 1 and there is never any other faults to go with it.

It has previously had a set of genuine merc coil packs,and a new air mass meter ( merc again )
I have replaced the coil pack loom due to an insane amount of punctures where someone had been cutting it open to test continuity i guess.
While I was at it I swapped injector cyl 1 with injector cylinder 2 but the problem still persists.
I have scoped coil primarys , air mass and injectors and all seems well but 15 miles later ...
I'm running out of hair to pull out

Hi
have you considered mechanical fault, e.e low compression, valve sticking /lifter issue ?

Cheers Aidan

Engine type 2.4? Assuming it is a 271 engine then the following is true.

Are there, or have there been any other codes besides the misfire codes for cyl one?

There is a valve guide issue on this engine that effects cyl one but there is also a breather pipe isssue that can log a misfire code for cyl one along with trim codes.

Carry out a cylinder leakage test on all cylinders hot and cold, you will find the reason for the miss fire code. HTH

Regards Mark.