i have a very weird question. i have talk to every tech i know and even talk with the z expert at the dealership and nobody knows what is wrong with m car. i problem is i have very low oil pressure. the specs for the car is 9psi at idle and between 53 and 65psi at 3200rpm. my oil pressure have never went over 35psi and drops to 0 or close to it sometimes. so because my oil pressure is so low it is causing my lifter to tap but not all the time. the tapping noise comes and goes at random. i have replace the engine(long block) twice and both engine have less than 20k miles on it. i also replace the oil pump, oil cooler, oil pressure regulator valves, new turbos, new vtc solenoid's, new vtc springs(the ones in front of the intake cams). also i always use full synthetic 5w-30 or 5w-40 oil and always use Nissan filter. so far we have rule out some of the possibilities like the bearings, lifter, all the new parts i have replaced. i am completely out of ideas and so is the shop and all the techs i have talked to. please help, thank you