FEKO solver method

Jey

What would be equivalent method in FEKO for a HFSS FEM – IE simulation, Antenna using FEM with FEBI boundary & other car model solved using IE solver

Mel

That would be FEM/MoM or FEM/MLFMM. 
So if you have a car with an antenna with much geometric details and dielectrics, the antenna part it is often solved more efficiently with FEM. 

The car body is solved with MoM, or if the car body is electrically large, MLFMM.

 

The following videos (two parts) demonstrates using the FEM/MoM efficiently.
https://altairuniversity.com/learning-library/stacked-dielectric-resonator-antenna-2/
https://altairuniversity.com/learning-library/23068-2/

 

In the video, the ground plane is the MoM part. For your application, the car body and other surrounding geometry would be the MoM part.