Emissions light is on and blinking i jus did a complete tune up?

my van emission light is on and blinking i jus did a complete tune up. new injectors ,plugs, coils, gasket. new crankshaft position sensor and camshaft position sensor on bank 2.. fixed the problem i was having stalling out so it ran okay ,, i drove around for a day now broke down again with flashing emission light ... getting codes saying misfire cylinder 3 and multiple misfire , lost communications/w com and poor voltage .... tested my alternator and is fine ... dont know why im getting misfire when i jus replaced with all new parts ... thinkink im having a faulty o2 sensor but no codes pop up for that ... any suggestions and help to figuring out the issue