I had my 87 XJS V12 starting and running all week from Monday to Friday. Come today Saturday and engine won't start at all. Added fuel even though it was half full. Cranks strong but won"t start at all. Don't really know what to look for. Any input from you guys is most appreciated.

 

Does the fuel pump run? If you turn the key to on, but don’t try to start it, you should hear it run for a few seconds.

I had a fuel pump relay fail randomly on me. If you don’t hear the pump, check the relay. If you do hear the pump, the relay is fine.

 

If Gareth's point checks out OK, I suggest:
Ignition on, floor the throttle pedal while someone listens to the injectors, they should click once as you floor the throttle (a Grant Francis diagnostic tip)
Check for spark. If no spark:
Check that there is 12v to the coil, ignition on.
Check that all the leads to the coil are intact, the copper can break inside the connector insulation
Clean the resistor pack plug connector
Check the plug, lead and mid-point connector on the twin wires from the coil bottom to the Lucas amplifier
Check the (dreaded) white wire from the amplifier that goes rearward into the engine loom to ensure connector OK and wire intact and not shorting out to the shielding

 

Thanks all for your recommendations. I shall follow through on Monday and come back with updates as soon as problem is solved.