Well I've been having this problem with my 2003 g35 coupe 138k miles. When I first got it. It had a miss fire amongst other problems I didn't take to notice. When I fix that one kiss fire it was running very powerful like it was suppose to. Then it went bad in 3 days. He fixed that one spark plug and it wasn't missing anymore but I have a major power loss.i initially ended up changing the spark plugs with auto lite double platinum. No change. Then I checked the codes. It went and it had a knock sensor and camshaft sensor code.
Changed them with ones I bought from Napa and still had a knock sensor code and the other went away. So i read more into it and it mentioned the harness. So I bought it from z1 and nothing changed. Changed the o2 sensor. 2 from eBay . I bought 2 down stream by accident and install them. I later bought up stream then changed it. The mechanic convinced me it was maybe the crank shaft and then we changed that. Still experiencing power loss. So in all I changed

Auto lite double plat spark plugs. Autozone
Knock sensor from Napa
Knock sensor harness z1
Camshaft Napa
Crank shaft auto zone
O2 down stream eBay oem
02 up stream Amazon oem

I don't know what else I need to do or what's wrong. Plz I need sum feed back. Last code I have was knock sensor P0327 and o2 sensor P0031

 

What about coil packs?

 

Coil packs? Sorry don't know what there suppose to do let alone change them

 

they sit on top of the spark plug and up the voltage high enough to get the plugs to spark.
if one goes out you won't get spark from that cylinder and it will give you a misfire.

 

b.
My question is. Would that cause a code to pop up . I changed a lot of parts already and my car been running like **** for months now.

 

If you open the bonnet with the car running and unplug one coil pack at a time to test them.
If you unplug one and the idle doesn't change, it means it wasn't doing anything (dead)

 

Okay is it possible that there probably dying? Or just very week because if I do that. I would just get a miss fire. And I currently don't have a miss fire

 

Oh I misread and thought you still have a misfire.
What about MAF sensor? I'm sure someone on here can help you with the codes

 

Rather than throwing parts and $$ at your G that haven't done much to change how it runs, find a mechanic that has the knowledge to fix it right the first time! Look at all the time and $$ you could have saved.
Gary

 

yep like gary said a good mechanic is def worth his weight in gold. get it done right the first time and you dont have to do it over again.

 

I've actually tried and either the mechanic is telling me the car drives "fine" or it's a part that I already changed and don't take me seriously like I have no idea what I'm talking about ( I'm 19)

 

Well as an update I believe the mechanic changed the wrong sensor. So I want to know how many o2 sensor does the car have. I read one place there's 4 & another place 3. Which is it?

 

i see 4

 

Also how many knock sensor does this car have ? Cause he trying to tell me the car has 2

 

The car has 4 o2 sensors cause it is V6 engine 2 each cylinder pack, 1 before cat. conv. and 1 after cat conv. same other side.It is very easy see it under the car. No science.