What are the common causes for fuel injectors not spraying or driping on a 1987 Chevy Blazer 2.8 L tbi?

I'm getting fire to the injectors when I use a test light. I can crank the vehicle when I pour fuel into the TBI, but it will only run as long as it takes to burn off the fuel. Ive checked the fuses for the ECM and they appear to be fine.