This workshop service manual provides comprehensive technical information for the Case 4-390, 4T-390, and 4TA390 diesel engine series. These engines, featuring a 4-cylinder configuration and approximately 3.9 liters of displacement, are designed for robust performance in demanding applications such as construction, agricultural, and industrial equipment. Their engineering emphasizes reliability and durability, making them a trusted choice for heavy-duty operations. The specific power and torque outputs vary across the different engine variants, reflecting their tailored capabilities for diverse operational needs. This manual serves as an essential resource for maintaining and repairing these Case engines. It covers critical areas including detailed maintenance procedures, diagnostic and troubleshooting guidance, and essential technical specifications. Owners, mechanics, and technicians will find the information necessary to ensure optimal engine performance, longevity, and safety. The manual is presented in English and is intended to support a wide range of model years for these engine series.