||using a long wood dowl or long screw driver and touch one end on the injector cap and the other end at your ear. If clicks present the injector is firing, if no click could be dead or no ground signal from the ECU. However it could also fire and be out of ohm spec (10 to 14 ohms) and on it's way out. Also check the coil by switching to a good coil from a firing cylindere.
Do these simple tests before spending $$ on injectors.
Not saying your guy is not a good mechanic but be carefull of guys that work cheap and maybe do not know the Z) because a 6 injector replace + rail involves a plenum pull and a lot of hoses and checking for fuel leaks and air leaks before reassembly of the plenum.
ZUL8TR in Orlando,FL