So after the shop put the engine back together, the problem started, and he didn't take it back to the shop?
Cause of injectors not firing if the injectors aren't bad- insufficient signal. Check the wires from the injectors all the way to the ECU. Use a multimeter to check resistance between the injector plugs and the ECU end of the wires.
How to check if an injector works: Connect a 9V battery to the injector and if it clicks, or you can feel it click, it's good. Do not connect it to a 12V car battery. a 1.5V battery won't be enough. Use only a 9V battery.