Hard staring after sitting a while

Connect a fuel pressure gauge and see if it drops over an hour or longer. Pressure is supposed to hold for weeks. If it drops over time, suspect a leaking injector.

To verify fuel pressure is causing the problem, turn the ignition switch to "run", wait a few seconds or until you hear the hum of the fuel pump stop. Turn the switch off, wait a few seconds, then turn it on again. Do that perhaps a third time, then try to start the engine. Each time you turn the ignition switch on, the fuel pump will run for one second. Two or three seconds should be enough time to build fuel pressure high enough for the engine to start.