was it ever said what killed him? was it something like head trauma or something?

there are no detailed informations to find.

just found informations like this:

On July 7, 1983, he was returning home, from a dinner engagement at the Clearwater Bay Golf Club. He was returning to the Kowloon area in a car driven by his elder brother. The car took the bending roads to fast and crashed into a cement wall on Clearwater Bay Road. Fu Sheng was rushed to United Hospital with serious injuries, and died three hours later. He was 29.