I am an Irish citizen as is my mother. However my father is an american citizen that lives in america. We are not in contact but I am in regular contact with my grandparents, his mother and father. I am just wondering if I am entitled to american citizenship? Can I apply to be a citizen without my father sponsoring me in?

There are many other factors involved... where were you born? Were your parents legally married? If you were born overseas, has your father reported birth of US citizen to the nearest US embassy after you were born? Etc.

I was born in ireland. My perents were not married. They were separated when I was born. And he did not report my birth. He is not on my birth certificate either but has acknowleded that he is my father.

If you are now over 18, nothing you can do. If you are under 18, you would need your father to fix this for you.

Easiest is you will travel to the US, and apply for naturalization. Your grandparents can sign the N-600 form. Since you have maintained a relationship with the grandparent then that should be the easiest way to go if the father is reluctant. One of the questions for your visa will be if you plan to immigrate. The answer is no. You are not entering the US illegally with your IRE passport with the intent to immigrate because you are not an immigrant, you are already a natural citizen and natural citizens do not immigrate. If you are outside the US, then you will be in the prove your case position to enter the US . The reason I say travel to the US, you can then apply for a passport and the N-600 will be included with the passport application and the certificate will be issued with the passport. You will have far more rights available to you once you are on american soil because once you are in the US you will be non-deportable.
It is no longer a matter of proving citizenship to enter the US, it would then become the burden of the US to prove you are not a citizen to deport you. Circumstantial evidence of your relationship to your grandparents would be sufficient to stay any order of deportation. The US simply cannot deport a US citizen by birth even if the evidence is incomplete. If you enter the US then be prepared to stay through the entire process