I have a 1991 z28 5.7 TPI, it randomly shut off on me a few days ago while driving and refused to start. got it home and the next day it started but would not idle, my IAC was bad so i replaced it and boom she roared back to life. on the test drive she shut off again. which takes me to where I am today. I can get her to fire over and run for 15 to 30 seconds then she cuts off with authority, no if ands or buts, no amount of mashing the throttle to try and save her she just dies. Sometimes she will fire up again and I can keep her running by giving her high throttle. but when the rpms drop she dies again. Other times she just spins over and wont crank. I know she is getting spark(force start with starting fluid.) and I know she has fuel (43 psi). Im at a loss guys, she is my DD and I cant afford to keep throwing parts at her.

Is it possible my ecm is wigging out and shutting off my injectors for some reason. The only code is a code 42 which i have been battling for a year, i have replaced everything but the ecm. I have a video of the car.

 

Code 42 is the electronic spark timing error code. Sounds like a faulty ignition module.

 

It's already been replaced

 

The Closed Loop Warm Timer is set to 30 seconds stock in the factory bin, meaning that when you restart the engine when warm, the engine will be in Open Loop for 30 seconds then switch to Closed Loop. When you start the engine when its' cold, the the Closed Loop Cold Timer is set 120 seconds, not to mention other criteria needs to be met as well, so it will take longer to reach Closed Loop. This is why your engine runs better (longer) in the morning, or when sitting for awhile. Judging from your video, your engine is warmed up, and exactly 30 seconds subsides when you start the engine to when it stalls, twice, so it is stalling the moment it reaches Closed Loop. Make sure your O2 sensor is connected, not to mention functional...

 

I noticed that as well I swapped my o2 for a good one and nothing changed. Anything else that could cause immediate closed loop shutdown