If the vehicle has an anti-theft system (VATS), it mi8ght be worth looking into that.
You should also measure the resistance of all the injector coils. If any are less than 11 ohms, they are suspect. Unplug those with lower resistance and see if the engine will start on the remaining injectors. The Multec injectors used in that vintage car are highly prone to insulation failure of the solenoid coils.