This comprehensive Mercury/Mariner Outboard Marine Service Manual covers 135 HP and 150 HP Optimax Direct Fuel Injection (DFI) models from 1998 and 1999. This manual is your essential guide to servicing and repairing your outboard engine. It provides detailed step-by-step instructions for all aspects of maintenance and repair, ensuring you have everything you need to keep your engine running smoothly. The manual begins with a detailed specifications section, outlining key engine dimensions, operating parameters, and essential component information. This section covers everything from overall length and weight to recommended fuel types, engine oil specifications, and gearcase oil capacity. The maintenance section provides a meticulous breakdown of scheduled maintenance procedures, along with recommended intervals. This section covers essential tasks such as spark plug replacement, fuel line inspection, engine oil changes, gear oil changes, lubrication point maintenance, and much more. It also includes detailed instructions for adjusting idle speed, checking ignition timing, and inspecting essential components like the water pump, timing belt, and balancer chain. The general information section provides essential identification numbers, tightening torque values, service data, and cylinder numbering. It also covers propeller recommendations, recommended fuel types, and warm-up procedures. The electrical section includes detailed instructions for inspecting, removing, installing, and troubleshooting essential electrical components like the starter motor, battery charging system, and tachometer. It also provides guidance on testing procedures for key electrical components, ensuring you can diagnose and repair electrical issues effectively. The ignition system section dives into the intricacies of your outboard's ignition system. It provides specifications, special tools, and troubleshooting guidance for components like the crank position sensor, ignition coil, and ECM. This section allows you to understand the workings of the ignition system and address issues related to starting, idling, and performance. The carburetor section, applicable to models equipped with carburetors, provides comprehensive guidance on carburetor adjustment, rebuilding, and inspection. It includes detailed instructions for removing, disassembling, cleaning, and reassembling the carburetor, ensuring you can restore it to factory specifications. The EFI system section, applicable to fuel-injected models, offers detailed information about the electronic fuel injection system. It covers key components like the fuel injection pump, fuel pump, throttle body, fuel lines, fuel rail, and fuel pressure regulator. This section provides valuable insights into the operation of the EFI system and guides you through troubleshooting and repair procedures. The powerhead section delves into the heart of your outboard engine. It provides detailed instructions for dismantling, inspecting, and reassembling the powerhead, including the cylinder head, crankshaft, pistons, and other essential components. This comprehensive section allows you to perform full engine rebuilds or address specific powerhead problems. The mid-section section covers the critical components that connect the powerhead to the lower unit. It provides detailed instructions for inspecting, removing, installing, and cleaning components like the engine side cover, driveshaft housing, oil pan, swivel bracket, steering bracket, and water pressure valve. The lower unit section focuses on the vital components that propel your outboard. It includes detailed instructions for inspecting, removing, installing, and repairing components like the gearcase, propeller, lower unit gears, water pump, shift guide housing, and propeller shaft components. This section is crucial for addressing issues related to gear noise, water pump malfunctions, and propeller performance. The manual also includes sections on attachments, control linkage, throttle/shift linkage, tiller handle, manual starter, diagnostic troubleshooting, and wiring diagrams. These sections provide valuable information for understanding the overall operation of your outboard and diagnosing and resolving complex problems.

This comprehensive service manual provides detailed instructions and specifications for servicing and repairing 1998 and 1999 Mercury/Mariner 135HP and 150HP Optimax outboard motors. It covers both the 1998 models, as well as the 1999 135HP and 150HP models, ensuring comprehensive support for your specific engine. The manual features detailed step-by-step procedures for each component, ensuring a clear understanding of every process. It includes detailed illustrations, diagrams, exploded parts views, pictures, service information, and troubleshooting tips for each section, making it easy to navigate and understand even for novice mechanics. This digital manual is conveniently delivered in PDF format, allowing you to download and access it instantly on any computer. The manual covers a wide range of topics, from basic maintenance tasks like spark plug replacement and oil changes to more complex repairs like rebuilding the powerhead or replacing the lower unit. It includes specifications for each component, maintenance schedules, and recommendations for troubleshooting common issues. You'll find sections dedicated to electrical systems, ignition systems, fuel injection systems, powerhead components, mid-section components, lower unit components, and more. Additionally, the manual provides information on attachments, control linkage, throttle/shift linkage, tiller handle, manual starter, diagnostic troubleshooting, and wiring diagrams. With this manual, you will have all the resources you need to confidently perform maintenance and repairs on your Mercury/Mariner 135HP or 150HP Optimax outboard motor.