I have an 89 Iroc 5.7. It will not start unless I use starting fluid.

Re-check your timing equipment set up and connect it to the #1 cylinder bank before re-checking timing. Sounds like your using the wrong cylinder spark plug for the timing light. Did you check to see if fuel is coming out if the fuel line when the engine is turning over ? When is the last time you changed the fuel filter ?

I am using the #1 cylinder. Haven't checked the fuel rail but once it starts it runs. I know there might be a couple of injectors that are not firing but is the timing the main cause for not starting?

Yes. If timing is off the engine will not start or run correctly, even if everything else is correct.

First, how many miles on the engine? If you are over about 150,000 you may well be due for a new timing chain and gear set. To check, remove the distributor cap, put a socket on the crank shaft pulley nut and rotate the engine using a breaker bar. If the engine turns before the rotor in the distributor, you need a timing chain, plain and simple. Set the timing correctly, and I would bet most of your issues will go away. Also, run fuel injector cleaner through a tank of gas every so often. It keeps the injectors spraying correctly. Lastly, if your O2 sensor is older than about 60,000 miles, change it, too. It affects air fuel mixture directly.