1996 Jaguar XJS #5 port not firing

With out the actual code I can't tell you what is causing it to come on. But a miss in number 5 cylinder are usually caused by a bad plug or plug wire. However there can be other problems that will cause this too. So what I would like you to do is call around to your local parts stores and find one that will do a free scan and have them scan you car. Now write down the code so we can find out what it is trying to tell us and have them clear the codes when done. Get back to me with the code number and we will go from there.