Why G35 coupe fuel pump does not fit to sedan? What is the issue with it, basically same car.

 

For the same reason the coupe has dual exhausts and the sedan does not. Different configurations.

 

But if you take the OEM coupe fuel pump off from the frame and put it on sedan would it work? The pump I asume is the same and dimensions also?

 

I would assume no because of different locations. Look at the part numbers and cross reference between the coupe and sedan. If they're different, then they are not interchangeable.

 

Only matter is the size, are you sure that coupse fuel pump size is different. If I look the photos of coupe pump and sedan pump to me seem they exactly identical nevertheless pump ref.nr. is different. I think the location does not matter cause the white frame is outside looking bit different but the size(lenghth and witdth should be same and also the holes)