98 XJR, 130,000 miles -- I'm having trouble starting when the engine is hot, after running it for a while. It fires up no problem from cold start. My engine is a probably Nikasil victim - I suspect my starting difficulties are from lost compression; however, why does it fire up right away when cold, but has a long crank, or trouble starting at all when hot?

 

You probably have leaky injectors. Try performing a fuel pressure test while blocking off the return line. If you can get one with a valve on the feed side of the gauge, even better. Then you can only test pressure on injectors. The cold start being normal kind of rules out the check valve in pump as fires right up.
You may be able to fix with a fuel injector cleaning, but experience says normally you need injectors replaced.
what state are you in out of curiousity. Southern states have big injector problems because of sulphur in fuel.

 

Thanks FJT. I'm in Indiana - fuel is BP 93 octane - hopefully not sulphur high, but who knows. I might try cleaning injectors, as you suggest. I was also going to replace the fuel pump relay (only 10 bux) - I've heard that in other cars, a bad fp relay can lead to hard starting when hot - not sure if this is true in jaguars or not.