This Service Workshop Manual covers the Case 4-390, 4T-390, and 4TA-390 internal combustion diesel engines. These engines, featuring a 3.9 L displacement and equipped with aftercoolers and turbochargers (HX25W, HX30W models), are engineered for robust performance and reliability in demanding applications. The manual details various fuel system components, including fuel injectors and CAV, Bosch model VE, and Bosch model A fuel injection pumps, underscoring the advanced design and intended use for service and repair. This comprehensive 342-page English-language manual provides essential information for maintaining and repairing these Case engines. It includes detailed procedures for critical components such as the cylinder head and valve train, cylinder block, balancer, cooling system, and fuel system and filters. The manual serves as an indispensable resource for owners, mechanics, and technicians, offering the technical specifications and guidance necessary to ensure optimal engine performance and longevity.