Is this Passlock security? The bcm and ecm have a security password that requires 'marrying' each other thru a procedure. Dealers use their scantool to marry these components in 10 minutes. Diyers without GMs scantool must perform three 10 minute ignition on cycles to marry these components. The ignition switch contains an embedded resistor that's learned in this procedure before security allows normal starting. GM may disable injectors when a theft attempt or security parts are replaced without a relearn (marrying) procedure. Passlock security flashing indicates either a theft attempt or relearn not performed to turn it off. If off during starting then verify spark and removing a spark plug to smell it for gasoline. And check for blwon fuses.