The following more general common rail info, rather than specifics of the JK engine.
The faster starter speed is probably lower compression due to any reason other than no fuel, being injected, as the injection of fuel adds to the compressed volume and the combustion resistance particularly when pre-injection or sometimes called pilot injection occurs.
It maybe an issue with a sticky shutoff solenoid valve/ pressure regulating valve not initially opening fully or maybe the high press pump is not building pressure rapidly.
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