Help before I go crazy. 99 suburban 5.7 vortec wont start.

[rickpilgrim]

I would first dump a cup of fuel down the throttle body and try to fire it up. That will either make it start and quit, make it start and run, or do absolutely nothing. Doing that will tell you if your problem is or isn't fuel related, nothiing more or less. Please keep in mind here I'm talking about a shot glass sized cup here, nothing more that would flood the motor.
Now if it starts and quits then you have to look futher. That cspi system is a sealed assembly, meaning you can unplug the fuel lines, unhook the main wiring harness, replace the fuel pressure regulator and that's it. There are no individual injectors per say, it is a spider assembly that has fuel lines that plug into the intake and the main wiring hookup and fuel line hookups and beyond the regulator is non serviceable.
So if you dont have the GM service plug to hook up a diagnostic meter to that main plug the next best way I know to test it is to pull off the upper (plastic) intake, pull the little hoses out of the lower(aluminum) intake and leave them out where you can see them. Hook the main fuel lines up, the wiring back up,unplug the coil wire from the distributor so it doesn't start and crank it over to see if it is spraying fuel out of the 8 little lines. If nothing then you have to replace that cspi spider assembly with a known good unit and repeat the test to see if it sprays fuel.
If you still have no fuel spray the problem is in the wiring or pcm and the way we find that is to hook up our Modus and test the system from the diagnostic port first and if thats good it's a wire by wire test from the PCM to the system and very time consuming, not to mention very unlikely unless the wiring got damaged in the engine swap. Do keep in mind here this is a 5 volt system on the computer system, DO NOT apply 12 volts to any part of the PCM system as that ruins parts fast.