1993 xj v12 red hot catalytic converter
 

Marelli ignition failure, most likely

Tons of archived info

Cheers
DD

If I swap Ignition power module the problem should go to the other side, if has one per side..

The 1993 and 1994 "XJ81" (factory code for the XJ12 in that body style) used the Marelli ignition as Doug has indicated. The fault is in the distributor rotor (very common!) - it must be replaced and only aftermarket rotors are available. The catalytic converter is overheated because the fuel from one bank of the engine is continuing to be poured through but has no spark to ignite it. What you describe is the exact scenario when the rotor fails.
In any case, this is the wrong forum for this car.
This forum deals with the V12 only to (and including) 1992 (and those cars did not use the Marelli ignition).

A member of my Jag club used to have an XJS with a Marelli ignition that caught fire, which he rebuilt and renamed Phoenix.
Within a year it caught fire again, but this time the fire dept was unable to save anything and it went to the Great Jaguar Graveyard.

He now drives a Chevy HHR.
(';')

Right, if the module is the problem

Might be the coil

But check the distributor rotor, as Gregory mentioned. They are known for burning out

Cheers
DD

And it caught fire (twice) because of the failure of the rotor and the resultant ignition of the excess fuel (from one bank of the engine) in the catalytic converter. Once is a surprise; twice is a lack of preventative mainenance...but within a year is a sign that the rotor was replaced with an aftermarket rotor - and these fail even more frequently!

I agree on all counts!
Maintenance is Not his strong suit, only if it completely prevented him from finding the nearest pub.
Now that he was Forced by his own negligence to acquire another car, he's happily making his rounds again.
(';')

Tino:

The forge aka "hot cat" might have "welded" the shift cable at it's terminus on the transmission.

Go down and under and see if it is still in place with the housing fiirmly clamped and the crimp[ sound.

Jaguar shift issues often cable related.

Search the archives. I've read of a modification to the distributor to assist in avoiding this issue. Errant spark. This system is two six cylinder distributors, one stacked over the other.

Carl