Cranks has fuel pressure and spark, no start just replaced ign switek for no spark problem 04 olds alero 3.4L

Do yourself a favor an have a qualified repair shop look at . Before you buy more parts the vehicle doesn't need . A qualified repair shop would have fix it for less then what you put into it. Some people just are not meant to fix their own cars .

Make sure battery has a full charge. If it cranks good but won't start, have a helper crank it while you visually check for spark at the spark plugs. If spark everywhere, use a gage and check proper fuel pressure and fuel injector pulse.
Any applicable trouble codes? Your obd1, you should be able to check some codes, yourself, if there are any.

Pull a plug wire , set the end close to the engine, crank it and watch for spark. No spark could be the cranks sensor, wires, ignition module , fuse, or PCM. Have the codes read. Could be the fuel pump too. I have had them die shortly after installs.

Did you check for spark at any ot the spark plug wires/ coils? If there is, check for fuel pressure at the fuel rail. Take the port cap off and connect a fuel pressure gauge. If one is not available, with a pocket screw driver deppress valve at port and observe if fuel pours out. If no fuel comes out at all, check your fuel pump circuit. Check for good ground and power at fuel pump connector. If power/ground are ok, replace fuel pump. If spark and good fuel pressure is present, there is the possibility of engine mechanical issues(jumped) timing chain). Also, a plugged catalitic wont let engine start but its very unlikely thats your problem. Start with your basics: spark, fuel, engine mechanical and catalitic.

If it cranks good but won't start, have a helper crank it, while you visually check for spark at the spark plugs. If spark everywhere, use a fuel pressure gage and check proper fuel pressure. Also, check for fuel injector pulse, engine cranking. Those are basic tests.

Can you check for applicable trouble codes? To check codes, yourself, at the least, you need an obd2 code reader.

Do you test the spark and the injector pulse of injectors

check fuel pressure.sound like fuel pump not working.fuel pressure should be 41 - 47 psi. if not replace fuel filter, still too low pump faulty, if you not getting fuel pressure, pump still not working check fuel pump fuse and relay.code scan car first look for fault in pcm.it controls the fuel pump relay and fuel pump.

IF YOU REPLACE CRANKSHAFT SENSOR IT HAS TO HAS TO BE RELEARNED USING TECH 2 SCANNER.FOR THE IGNITION KEY REPLACEMENT.TURN IGNITION SWITCH TO THE ON POSITION FOR 10 MINUTES WITH ENGINE OFF.WHEN SECURITY LIGHT TURNS ITSELF OFF.THEN YOU TURN OFF IGNITION SWITCH FOR 5 SECONDS.THEN START THE ENGINE.

No that would stop the spark you said you have. fuel flow anf fuel pressure are to different things. did it flow or really blast out of the line?

3.8 are known for ignition trouble but first use the fuel release valve located on top of engine under a screw cap to see if your getting fuel. It takes 4 things to make engine run fuel spark air and compression. But most likely the Ign control module or crank sensor. So try this
1) check the fuel pressure
2) check for spark
3) compression test