Ok, So I have a few problems that Im fixing with my car first off Im cheap so I don't spend money I don't have to. Since I bought my car the trunk has always been hard to close I'd have to slam the trunk closed and if it didn't grab I would have to hit the trunk release and try again servral times. Also When you open the trunk it would make a terrible grinding noise, So I decided to take it apart and see what was causing this since I knew that it was not normal even though I've seen threads that say it is. So to start off this write up you will need:
-10mm Wrench or socket
-12mm Wrench or socket
-Small tipped phillips head screw driver
-Small amount of grease
-A small screw the size of the ones you take out of the motor case I dont have measurements but any small one will do.
-Small drill bit and drill
-Small circular piece of plastic (you can improvise with this) I used a Plastic petcock drain plug for a radiator.
This fixed my problem and Im not 100% sure it will fix yours but you never know untill you take it apart and look on the inside of the motor to see what is causing the problem, in this case mine was caused because one of the rubber stoppers were missing. It looked as if someone tried to fix it before and failed. Attempt at your own risk! This was also done on a 2003 model 350Z.
Step 1. Open the trunk and remove the carpet and the spare tire plastic board out of the trunk.
Step 2. Pull the bottom of the rear panel out towards the front of the car it will release the clips then pull up on the panel towards you, this will release the four or five other clips.
Step 3. Remove all six 12mm bolts.
Step 4. Unclip the open/close sensor for the trunk.
Step 5. Unplug the motor clip.
Step 6. Pull the latch and motor assembly out and push up on the tab that connects the rod to the latch assembly.
Step 7. Unscrew the motor assembly from the metal plate using a 10mm wrench or socket.
Step 8. Remove the two big phillips head screws from the brace that holds the motor on to the assembly. I had to use vise grips as they were really tight and I almost messed up the screws.
Step 9. Remove all seven small screws from the motor then pry it open carefully so no pieces go spilling out of the motor. If you pull any of the gears out your going to be in trouble unless you know how to reset them, I do but I took no pictures of this process and is hard to explain without pictures so "DONT" spill anything out.
Step 10. Identify what is causing your problem, mine was the rubber stopped was gone I have no clue where the hell it went but it wasnt there. There was some crumpled up electrical tape that looked like some one tried to fix it but they didn't.
Step 11. If the stopper is damaged or missing on yours continue. Find a small piece of plastic that is about the same size as the stopper on the other side and cut it to fit. Take the top cover (the part without all the gears in it) and cut the small circle tab that is sticking out above where the stopper should have been (it will get in the way when installing the new plastic stopper).
Step 12. Size up the lid on the motor assembly and figure out where your plastic stopper will be sitting under the lid and drill a small hole through the cover and through the center of the plastic stopper. The reason for this is so the stopper doesn't move around in the motor assembly.
Step 13. Once this is done drill a small hole through the center of the plastic stopper. Then use the small screw and screw the plastic stopper on to the lid, It doesn't have to be pretty because nobody will be looking at it when its all sealed up it just has to work at stopping the swing gear that unlocks the trunk.
Step 14. Almost there make sure that when you put the cover on that both go together flush. If not then you made a mistake and hopefully you can do something to fix it. Also add a tad of grease if you think it needs it, I did because it was pretty dry inside. DO NOT add alot of grease the springs that return the arm to zero are not that strong and if you have alot of grease it will prevent it from returning to zero where it should be.
Step 15. Reinstall all seven screws. only tighten them snug if you over tighten them and strip the plastic your screwed.
Step 16. Plug the motor assembly back in to the power clip, Install the metal rod back onto the latch assembly bolt everything back down snug and take the phillips head screw driver and push down on the lock to simulate the trunk closing. Once its latched trigger the trunk release and see if you did it correctly if so it will release and you are a winner.
If not unbolt everything again and pull the whole assembly out without unplugging the power, hit the switch and watch the arm to see if it is moving. If it is not moving you do not have the gears inside lined up correctly and they need to be reset.
If it is moving but does not travel the whole way to unlock then the gears are not lined up correctly.
If it is moving and unlocks the trunk but doesn't return to its original position and you can manually push the rod back and forth then you used to much grease inside the motor.
If it is moving and unlocks the trunk but doesn't return to its original position and you cannot manually push the rod back and forth then something inside is not positioned correctly and should be reinspected.
Step 17. Reinstall all components and plugs. See instructions in reverse.