So, after helping diagnose some of the issue with my friend's 2004 XJ8 (4.2L), after driving it for some time after you shut it down and attempt to restart, it is very hard to start, or stumbles, or refuses to start. It almost seems like vapor lock to me.

I know the older convertibles had fuel pump issues as I have replaced them, but they would just fail outright. According to my scan the car was getting 55.5 psi of fuel pressure when running, so not sure...

Anyone experienced this kind of behavior?

 

Maybe a temp sensor (probably IAT if it has it) that's wrong or a dribbly injector.

 

I was also thinking the dribbly injector route. Going to hook up my fuel pressure gauge and see what I get when shut off.

For the certified tech/those that know, the '04 XJ8s have a returnless system I've read right? So I'm assuming it should be holding 55 psi if the check valve/injectors are good?

Thank you!

 

The system pressure bleeds off in my experience. Might stay up a short while after starting or turning on the ignition. Definitely won't hold overnight. An air leak can appear as vapor lock. At least on 04 XJR, there is a resonator under the plastic intake elbow that will crack at the base/joint. Had it happen to me and just JB Welded it back in place. Chased the hard start for 2 months before I found it. I'll attach a picture thanks to a post from @Lagonia.


Air leak point

 

+1 on checking the temp sensor. I had a Jetta which had issues with the coolant temp sensor sporadically failing and sending out a default value of 170F, causing many of the same starting issues, but only when the sensor errored out to the default value on my scanner.

 

I had similar problem on my 2004 XJ8. It occured there was a poor connection on the starter, it was enough to make impression that the starter is cranking fast enough however when engine was warm it had difficultues starting. Then after fixing the connection problem went away.