Injection system test?

Hello Dear Sir
I have a Peugeot 206 16V and the yellow engine light is on about 11 mounths .
I changed wires ,plug,coil,clean service the injection system but still doesnt work .
Now the injection system doesnt work properly too, my mechanic told me i have to wait the injection system turn off (one from four piece of injection system) then will know which is not working then change that one.
I belive there is system which is for testing the injection system one by one and tell us which is damage.
Would you please tell me is there any free software available to download and test the system by myself.
Many thanks for yr help.

Best regards.
Farid