This service repair manual covers Mercury Mercruiser GM 4 Cylinder Marine Engines manufactured between 1989 and 1993. Specifically, it addresses MCM 3.0L (Serial Number OC856451 & Above) and MCM 3.0L / 3.0LX (Serial Number OC868143 & Above) models. These engines are known for their reliable GM In-Line 4-Cylinder design, featuring a 3.0L (181 C.I.D.) displacement and typically producing around 130-145 HP. They utilize a MerCarb 2-Barrel carburetor and are available in seawater or closed-cooled configurations, equipped with a standard ignition system. This comprehensive 348-page manual provides essential information for maintaining and repairing your Mercury Mercruiser engine. It includes detailed, step-by-step procedures, clear instructions, helpful illustrations, diagrams, and photos. The manual covers general maintenance, troubleshooting, and specific service tasks for critical systems such as the power steering, fuel pump, exhaust manifolds, and electrical components including starting, ignition, and charging systems. This resource is designed to assist owners, mechanics, and technicians in ensuring optimal performance and longevity of their marine engines.