'02 Saturn SL2 twin cam. Turns over but won't start. Warning lingts flicker.

Here's a link to your firing order Michael,join Autozone's site,they just need your Email address then you can use their repair guides for free. Specifications Firing Order AutoZone com

Yes ,the engine is identical, just twin cam instead of a single cam set up.

Have you checked whether it is on model?,does your vehicle can communicate with the variable sensors of the new engine? are the crank and cam shaft sensors the same on serial number or are different? Does the injection system gets the correct fuel pressure or is not sufficient.

If it is a random problem, you may have to wait until it is a solid failure to find the cause.
Could be the key switch, the neutral safety switch, the starter solenoid, or a cable connection.
A mechanic would check all of these components for voltage when it will not crank.

i have the same prblm 140k. i changd plugs, pvc, fuel fltr.. the problm is in the ******. i will chng atf and filter. if this does not solve prblm, it might be ****** valve body. ****** work $$$$$$$. i'm going to run it till it won't move no more than scrap it. i rpl ****** 3 yrs ago $800 (used ******).

good luck on your ride.

Maybe anti theft system shutting the injectors off. This link explains http://vatspasslockpasskeysecurityhelp.yolasite.com/

probably the crank sensor, above the starter on the firewall side-no crank signal, no fuel pump activation.

your pistons are leting blow by get through whick means that your pisten rings are wearing out more then likly

OK I don't know if this is your problem but my 92 sl2 is kinda the same way. my sl2s ECTS went out and it dose the same this is what it looks like you will have to remove the air duct to get to it and this is were it's located keep in mind there are two of them you want to unplug the one with two wires it is lower on the block. but do not remove it.

after unpluging it try starting your car if it starts them you will have to get a new ECTS Coolant Temp Sensor. btw don't drive around with it unpluged just becouse it runs dosen't mean you should use it like that.

check your throttle positining sensor.