This Service Repair Manual covers Mercury/Mariner Outboard engines manufactured between 1998 and 2001. These 4-stroke engines, featuring DOHC design and multi-point sequential electronic fuel injection (EFI), are available in 40, 45, and 50 HP variants. Engineered for reliability and performance, these outboards are suitable for a wide range of boating applications. The water-cooled system and electric starting ensure consistent operation, while the Forward-Neutral-Reverse transmission with optional counter-rotation provides versatile control. This manual provides comprehensive guidance for maintaining and repairing your Mercury/Mariner Outboard. It details essential procedures including oil filter, fuel filter, and water pump impeller replacement, along with ignition timing and idle speed adjustments. The manual also covers fuel line replacement and battery charging system tests. By following the instructions and specifications within this document, owners and technicians can ensure the optimal performance and longevity of their engine.