This manual covers the Case 4-390, 4T-390, and 4TA390 models. These diesel engines, featuring a 3.9-liter displacement and four cylinders, are designed for robust performance in demanding environments. Depending on the specific variant, they offer naturally aspirated or turbocharged aspiration, making them suitable for a wide range of applications including agricultural equipment, construction machinery, and industrial equipment. Their engineering is focused on reliability and durability for heavy-duty operations. The purpose of this Full Service Repair Manual is to provide comprehensive guidance for the repair, maintenance, and rebuilding of these Case engines. It details essential procedures, technical specifications, and troubleshooting information necessary for optimal performance and longevity. This document is an indispensable resource for owners, mechanics, and technicians seeking to understand, service, and maintain their Case 4-390 series engines effectively.