The Jaguar XJS from 1994 typically features a 4.0L inline-six or a 6.0L V12 engine, depending on the specific model variant. The "FF34" engine code generally refers to the 4.0L AJ16 engine, which is known for its smooth performance and reliability. This engine was part of Jaguar's efforts to modernize their lineup during the 1990s, offering improved fuel efficiency and emissions compared to earlier models. If you require more specific details about this engine, such as specifications or common issues, please provide additional context.