This manual covers Mercruiser PCM 555 Big Block diagnostics for Mercury marine engines. Specifically, it addresses sterndrive models such as the 496 MAG HO and 496 MAG, as well as inboard models like the 8.1S HO and 8.1S Horizon. These engines are characterized by their V8 configuration, 8.1-liter (496 cubic inch) displacement, and Multi-Port Fuel Injection (MPI) systems. The engines offer power variants including HO (High Output), Standard, and Horizon. Transmission options for sterndrive applications include Bravo One and Bravo Three, while inboard models utilize ZF Marine Transmissions or Velvet Drive. This manual is designed for engines with serial number prefix 0M and serial numbers 0M000000 and above.

The purpose of this Diagnostics and Troubleshooting Manual, number 33, is to provide comprehensive guidance for maintaining and repairing the specified Mercruiser PCM 555 Big Block engines. It includes essential sections on General Information, Troubleshooting, and Wiring Diagrams, all presented in English. Owners, mechanics, and technicians will find detailed procedures and technical specifications necessary for effective diagnosis and repair. The manual emphasizes the use of Mercury/Mercruiser Diagnostic Software and Interface tools, crucial for proper system analysis and maintenance of these high-performance marine powerplants.