This manual covers the Mercury Mercruiser 8.1 PCM 555, a marine engine diagnostic and wiring system designed for reliability and performance. Engineered for the demands of marine environments, the Mercruiser 8.1 PCM 555 represents a commitment to quality and advanced technology. This product category focuses on providing comprehensive support for the engine control module, ensuring optimal operation and longevity for your vessel. The purpose of this manual is to provide detailed information for the repair, parts lookup, and routine maintenance of the Mercury Mercruiser 8.1 engines, specifically those utilizing the 8.1 PCM 555 system. It includes extensive coverage of routine maintenance, engine removal and installation, fuel systems, lubrication and cooling, electrical systems, and advanced troubleshooting. This resource is invaluable for owners, mechanics, and technicians seeking to maintain, diagnose, and repair their Mercury Mercruiser engines effectively.