This manual covers the Case 4-390, 4T-390, and 4TA390 engine series. These diesel engines are characterized by their 4-cylinder configuration and 3.9-liter displacement, offering robust performance suitable for various industrial and agricultural applications. Engineered for reliability and durability, these engines are designed to deliver consistent power output, typically ranging from 70 to 120 horsepower and 180 to 300 lb-ft of torque, depending on specific configurations and turbocharging. Their liquid-cooled systems and direct injection fuel systems contribute to efficient operation and longevity. This professional-quality Workshop Service Manual provides in-depth repair and service information in English. It details essential maintenance procedures, including lubrication, filter replacement, and coolant specifications, along with recommended service intervals. The manual also covers technical specifications and troubleshooting guidance to assist owners, mechanics, and technicians in maintaining the optimal performance and extending the service life of the Case 4-390, 4T-390, and 4TA390 engine series.