I've realized over the past few weeks my xj has been having trouble starting in the morning and when I leave work in the afternoon. When she's warm she starts right up though...

I've heard it could be a check valve problem but have no idea how to fix my problem. By any chance could it be a crank sensor?

 

Well, when you say trouble starting, does it just crank for an abnormally long time before it catches, but once it catches it's fine. Or, does it repeatedly try to catch and seem like its stumbling, misfiring, or missing before it finally starts up?

If it's yes to the first question, I'd suspect fuel pressure issues.

If yes to the second question, it could be CPS. Or a weak coil. Bad ground. Lots of things. But yes, the CPS is historically the slowest gazelle in the herd and tends to die at alarming rates.