Well it is not the injectors all they way. Mechanics would say ti install low CC injectors to save fuel same like installing honda 125 carburetor to save fuel.
Get scanner hooked up to your system and tell us what is Short term fuel trim and long term fuel trim values. Is your O2 sensor giving correct readings etc. there is no way someone can tell you just like that here goes the problem. its not that simple. remember you live in world where they check your car fuel pressure by blocking fuel pipe with thumb and volume test by seeing speed of petrol flow.
Mechanics tend to be precise tools but they are not so you better dig it out your self instead of spending money on changing things.
if you have working O2 sensor good MAF/MAP sensor. Short term fuel trim within + and - 5 % range your car is at ideal situation. other than that you need to dig things out