i have 1.8 liter engine in my car, injectors were installed by previous owner. How can i make sure they are of right capacity ? is there any identification code ?

 

injector flow rates are more so matched to the expected HP rating of the engine rather than the displacement. a quick web search should provide you with some chart or rule of thumb for matching them.

I'm sure there must be some identifying mark or model number on the injectors to tell you what they are. look closely and post pictures if you're not having any luck figuring them out.