'97 Jaguar xj6 stays in open loop. emission sensors never ready. Drive Cycle fails

I understand that the dealership wasn't able to find the issue, but you need to take the vehicle to someone who specializes in electrical diagnosis. The PCM needs to see proper signal readings on all its emission control devices before it can go into closed loop. A PCM in 1997 is far worse at self diagnosis than current computers, so if a sensor isn't reading correctly but still reading and sending a value back to the computer, the computer may determine that there is no issue with the sensor, the car just isn't yet in the right conditions for closed loop. I've seen it a good number of times before.