Those are not the only things that can cause a misfire. Incorrect compression in that cylinder (4 I assume since they said Injector number 4) can cause a misfire as well as dirty valves or a bad ignition coil. Incorrect fuel pressure can also cause a misfire, but that would not likely be isolated to one cylinder. The O2 simulator wouldn't have an effect on a misfire code because that gets installed after the cat and is used to measure cat efficiency. I'm not sure which motor is in the 97 Z34, but if you can swap coils, I would do that and see if the misfire code changes to a different cylinder.

 

the plugs, wires, and coils are all good.

 

i got the O2 in today and marked another sensor off the list but still have so many left. IAT, IAC, etc etc. or even the PCM idk i might just sell it and buy and older camaro, im tired of OBII cars they suck.[:@]