too close, cant tell what it is

 

 

That's the Ignition Coil Capacitor. Common to the 2001 XJ and some 2000 XJ's.



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Thanks Ken, was wondering about that myself.
What's its purpose? Eliminating radio or pcm ignition noise from the coil pack?

 

Eliminating ignition noise from the PCM/radio. The ignition system can function without that capacitor. Don't know why the German engineers stuck their nose in this but it looks like they did when Daimler bought Chrysler

 

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when coils are switched on/off they generate high reverse voltages. that cap is an open for dc but acts like a short for the spikes that might be made.
the batt is like a giant cap but a long piece of wire can let spikes develope.

 

Haha did he seriously just resize the same pic? That's a good one.

 

Indeed he did.