02sensors codes
 

I have a 1990 300zx automatic Na , that has me spending a lot of money on gas, I'm only getting 10 mpg, I've changed all injectors, timing belt, fuel pump, alternator, and many more parts, I didn't change these parts because of the mpg, I just changed them because it was time, computer is giving is giving oxygen sensor codes but my z specialist mechanic says that he doesn't believe that the 02sensors is the reason why I'm getting bad gas mialeage? The works on a lot of z's I mean a lot he dynos the cars and everything but can't find the reason why such bad mpg, am I missing anything here withe the sensors, I have always believed that bad sensors = running rich= burning too much fuel. He says that not necessarily that's the case? Now what's your opinion, should I just change them anyways and please advise which ones I should buy, or other wise. The guy is good but this is just not jiving with me, I need some others advise, thanks

Does the car feel sluggish at all or anything?
So regardless of the fact that the mechanic thinks its not O2's...They are still throwing you a code...I would say you can try cleaning the connections first (and to add you can test them with a multimeter), and see if you get a code again, or just plain outright change them. I would recommend stock bosch sensors.

Injectors
 

You stated that you changed all the injectors, did you replace them with stock injectors ?