- Is it possible that these readings are not correct from this obd2 app ? Shouldn't they drop a bit and stay for 1-2 hrs?
sure it's possible the readings are incorrect but do you know what Hyundai says they should be, it's a ecm calculation that will vary based on engine requirements, it sounds like the pump may be operating correctly but it possibly could be showing signs of wear on the piston , albeit slight and intermittent.
-What regulates pressure AFTER car is off ? Gas tank press.regulator (one that sits on top of the tank, inside vehicle under carpet/back seat) bad?
nothing regulates pressure when off - the hpp has a one way value that prevents backflow so pressure can rise upon engine shutoff as one stroke of the piston can produce high psi and once power is cut the injectors close as does the power to the hpp control solenoid, the system is designed to hold high pressure in the rail, so if the pump is leaky or an injector pressure could drop - causing longer crank cycle.
I could not reproduce longer cranking times this morning while this obd2 reader was hooked up
check this vid out on scanning/interpreting pump readings, car with long crank but also loss of power at higher rpms - if you are not expereincing that I wouldn't replace the hpp.