Let's keep this simple.
TBI, ECU will prime fuel pump for 2-3 seconds when you turn the key to on or ignition. After it primes it will shut the pump off.
ECU, when ECU senses that the engine is turning over, signal from CPS, it will run the pump and send a pulse signal to the injector and allow spark.
CPS, if no signal to ECU, ECU will shut down pump and end pulse signal to injector and end spark.
If your injector is not pulsating- no signal from CPS to ECU. Or you have a wiring issue or you have a bad ECU.
It's that simple.
What ECU did you get to replace the original and why did you replace it?