2006 350z base model. So I had a problem about a year ago. I was having a misfire so I replaced the spark plugs thinking that was it, they needed replaced for sure, but that wasn't it. I then ran the codes and found out it was one of the coil packs, and not having enough money to replace them all I replaced it, but with one of a different brand, 5 bosch and now 1 Duralast, since I was having a misfire for a few weeks I didn't get on it at all, but now that I had it fixed I was gonna take for a spin. I then noticed that if the car is in gear and I try to give it more than 50% throttle it seems to almost rev limit me at 3k rpms. I could drive relatively normally so I just left it be and was gonna trouble shoot another day. Though I thought it might be the fuel pump.
I now have a new problem though, that I'm not sure is related. I got out of work one day and tried to start my car and it was dead. I jumped it and drove home, 45min drive, the next day it wouldn't start again so I tried to jump it again. No dice. It was getting power but not starting. After I tried to jump it a second time though the car still had power and my battery indicater reads above 12volts. About 4 days later I decided to check the fuel pump, and found nothing. The filter was fine and when I turn the ignition to "ON" and it pumps.
The only thing that I can think at this point is that coil pack but I was told, by a better mechanic than me, that it doesn't usually matter. Any info will help!
Thanks for reading!

 

Pull codes

 

I would check the voltage coming off the alternator and check the battery with a voltmeter, that gauge seems kinda pointless to me. Another thing to check would be all the grounds in the engine bay. I had an odd misfire issue because of a ground strap that was barely hanging on by a thread.

 

As trav said, pull the codes. If this is a high mileage Z, it's probably time to replace CAM and Crank sensors. Avoid aftermarket cam/crank sensors like the plague. These vehicles are notoriously picky about the engine sensors. You might even have caused more issues using the aftermarket coil pack (I would start here and go back to an OEM unit). OEM are more expensive for sure, but you avoid chasing your own tail and get that peace of mind. Beg or borrow if cash is tight, just use OEM when it comes to these issues. It's way better than purchasing aftermarket only to wind up having to use OEM in the end. Another option is used OEM parts, still a gamble and I wouldn't install used cam/crank sensors, but used coil packs are usually a safe gamble.
Good Luck!
-Icer