Method of operating a combustion engine

The invention relates to a method of operating a combustion engine (10), wherein an exhaust manifold pressure (p_em) within an exhaust manifold (12) is determined, characterized in that a cylinder pressure (p_c1) of at least one cylinder (13a) of said combustion engine (10) is determined (100) and in that said exhaust manifold pressure (p_em) is derived (110) from said cylinder pressure (p_c1).