Mercury Mariner 135/150 Optimax Service Manual (P/N 90-855347R1)

• Document identity and coverage: A 490-page PDF of official Mercury Marine Service Manual P/N 90-855347R1, January 1999, covering Mercury and Mariner 135/150 OptiMax DFI outboards with S/N 0G590000 and above.
• DFI fuel, air, and oil systems: Includes crankcase pulse fuel-pump testing and repair, vapor-separator service, low- and high-pressure pump tests, fuel-rail and injector work, regulator and tracker-valve service, air-compressor overhaul, and oil-pump priming and troubleshooting.
• ECM, ignition, and starting diagnosis: Covers troubleshooting with and without the Digital Diagnostic Terminal, sensor and injector checks, TPS adjustment, charging-system circuit tests, alternator repair, starter overhaul, warning signals, and multi-function gauge testing.
• Powerhead and cooling repair: Details powerhead removal, disassembly, cleaning and inspection, crankshaft/piston/connecting-rod work, reed-block and cylinder-head service, reassembly, break-in, thermostat testing, water-pressure checks, and cooling-system fault diagnosis.
• Midsection, trim, and gearcase work: Provides clamp/swivel and driveshaft-housing procedures, power-trim hydraulic and electrical testing, pump and motor repair, fill/purge work, plus separate overhauls for right-hand standard-rotation and left-hand counterrotation non-ratcheting gear housings.
• Factory diagrams and test aids: Includes labeled powerhead views and component illustrations, the 1998 and 1999 135/150 DFI Wiring Diagrams, Starter Circuit Troubleshooting Flow Chart, Air Compressor Flow Diagram, and separate 1998/1999 and 1999½ Water Flow Diagrams.

The manual is built around the 153 cu. in. (2.5L), 60-degree V-6 two-cycle direct-injected powerhead. It is not a generic OptiMax reference: its repair coverage is tied to the listed 135/150 DFI platform, the specified serial range, and the standard- and counterrotation gearcases shown in the publication. Mercury wrote it for dealer mechanics and company service personnel, assuming familiarity with similar outboards, trained service procedures, and access to common and specified special tools.

Early OptiMax Systems and Factory Procedures

Model-specific differences matter on these engines. The oil-injection chapter covers check-valve kit 21-858945A2 for 1998 135/150 DFI outboards through S/N 0G886266, while the cooling chapter distinguishes the original 1998/1999 flow path from the 1999½ arrangement. The electrical section likewise separates the 1998 and 1999 engine wiring.

DDT material goes well beyond basic fault lookup. It covers live sensor and ECM data, status switches, fault and run history, cylinder-misfire isolation, component output-load tests, oil-pump prime, and break-in status. A symptom-based DFI troubleshooting guide and non-DDT checks support no-start, rough-running, pressure, ignition, and injector diagnosis.

Installation coverage addresses lifting, transom mounting, single- and dual-engine rigging, remote harnesses, gauges, and shift/throttle cable setup. It also documents fuel-system filling, oil-system priming and air purging, trim-in and trim-tab adjustment, plus Ride Guide steering arrangements for single- and dual-outboard installations. Routine-service material covers scheduled maintenance, cooling-system flushing, component inspections, gearcase lubrication, storage preparation, and post-submersion service.

Specifications, Tools, and Repair Cautions

Factory reference data identifies the NGK PZFR5F-11 and listed alternative spark-plug applications, along with model-specific RPM and charging specifications. The tables also supply component torque sequences, fuel/air and cooling pressure checks, fluid capacities, electrical test values, cylinder and piston inspection limits, gear-depth and backlash data, and adjustment specifications.

Named tools include the Digital Diagnostic Terminal 91-823686A2, dual fuel/air pressure gauge 91-852087A1/A2, power-trim test gauge kit 91-52915A6, and pinion locating gear tool 91-12349A2. These requirements are important when judging whether a repair can be completed with the equipment already in the shop.

The DFI air and fuel circuits retain pressure, so the manual’s bleed-down and component-handling precautions must be followed before rails, hoses, injectors, or the vapor separator are opened. It also warns that blocked exhaust-cooling dump holes can melt the tuner pipe and damage the bearing-carrier prop-shaft seals. During lower-unit repair, lost shim locations or incorrect gear depth and backlash can cause noisy operation and premature gear failure.