Good afternoon Robin.
Thank you for your reply.
Its a 1989 xjs v12 5.3 sports convertible.
This morning I Started the car no problem, it ran well for about 5mins after which time the engine began to falter & cutout altogether.
It seems when the engine is running up to temperature it starts to lose power.
The engine cooling system if fine, no leaks, temp gauge reads normal.
Kind Regards.