I replaced my fuel injector # 3 and all spark plugs on my 1991 Nissan 300zx non turbo and my engine light is still on and my car still idles really weird and it smells like gas so badly all the time now when it sit in idle at a red light or at home ? Any help with what it could be and how to fix it?

Dirty fuel injectors.

It sounds like you have a blown head gasket. (Would explain why fuel injector went bad)

It sounds like the number 2 injector is hung open.

It will dump fuel and cause all sorts off issues with the ECU.

You should ohm that injector and compare it with the others to see if it is wildly different. If so, change it out and retest.

It could be a couple of things. I first guess is to check the fuel filter. If it has not been changed out within 15-25,000 miles deposits that within the gas tank has restricted the flow and will cause a hesitation or very rough idle. Now the desposit could have surface close to the injectors restricting the flow. Second, tune-up ( distributor cap and button, spark plugs, wires, etc). Third, check all you fuel hoses leading (especially leading from the fuel filter) to and from the engine.If they have never been changed, I would do so. Hope this a start of resolving your problem.

get a pair of pointy nose pliers start the car let the engine revs settle, when they have pinch off the return line from the fuel rail and see if the revs come up if so you have a injector problem and get the m cleaned (don't pinch off the hose to long as it will make a fuel leak only do it for a couple of seconds)

its running very RICH !!!! TOO MUCH GAS!
check the air fuel mix & the air filter!
it needs a good tune up!
& get the injectors either cleaned or replaced
the fuel injectors from the factory are renound for leaking & setting fire to this model!
you can buy aftermrket injectors that eliminate the this

dude, i think you have two spark plug cables cross over. go to your local autozone and find a "firing order" if it was a blown head gasket it would show on the compression test but i'm pretty sure its a spark plug cable cross over.

300zx auto will have 4 gears. 1-3 are normal running gears 4th is said to be an "overdrive" gear.

shift points should be under 4krpm, with light driving. my 300zx non-turbo usually shifts around 2-3K.

throttle position sensor could need adjustment or replacement. trans fluid should be checked to see if it's in good shape and full.

Don't worry about the comment posted above. As long as you dont have a miss-fire or the car isnt running rough your injectors are most likely fine.

There are a ton of small and short fuel lines that run on these cars stock. Just check all the fuel lines under the hood and you should see or smell a small leak on the hose itself.

There is no means of setting the timing if you are referring to a conventional timing light. The engine is designed with sensors that sense the angle of the camshafts in relationship to the crankshaft and whether it is on the intake or exhaust stroke on the #1 cylinder. This design is actually a little more complex than that because it has variable valve timing which means that the angle in which the camshafts open and close the valves, change with RPM's This give the engine the best of both worlds. It's like have an engine with cams designed for torque at low RPM and a set of cams designed for HP with a free breathing quick revving engine you would have on a race course. The ECM is constantly changing the timing and injector pulse width based on many sources of input, from, the O2 sensor, air flow, air temp, coolant temp, fuel pressure, RPM's and a host of other inputs.
SO>>>>>>>>>>>> in a manner of speaking, unless you are making reference to setting up the timing chain, everything else is under control by the ECM and related components.