My car cranking long to start. Recently I cleaned all fuel injectors, changed fuel pressure regulator, changed battery,changed plug wire and spark plug, changed fuel pump and filter, changed air filter. Now if I stopped my car for some time , then engine cranking to start.there is no check engine light. Recently I consult with a mechanic, he told me that, fuel is going back to fuel tank when I am stopping my car.so it will take time to develop required pressure to pump fuel from tank to injector.There is no leak from fuel injector. Can I go for a computer scaning

What's the point? You stated there is not a check engine light. Why scan the computer if it's not telling you it's storing codes.

I'd rather know what's missing during this extended cranking no-start...
When you're cranking, do you hear the fuel pump prime? Can you smell fuel while cranking? Can you perform a fuel pressure test?
Has anyone checked for spark during cranking?

What happened to all the parts you took off and replaced? The money spent on all those parts could have gone a long way toward paying for actual diagnostics rather than try-agnostics!