1987–1993 Mercury Mariner 70hp, 75hp, 80hp, 90hp Marathon Outboard Service Manual (P/N 90-13645-2)

• Mercury Marine factory service manual P/N 90-13645-2, printed in 1995: covers 1987–1993 three-cylinder 70, 75, 75 Marathon, 75XD, 75 Seapro, 80, and 90 models, plus 1988–1993 four-cylinder 100 and 115 models.
• Electrical and ignition diagnosis: includes the DVA sequence and test chart, plus stator, trigger, coil, switch-box, key-switch, charging-system, starter, solenoid, and armature testing.
• Fuel, carburetion, and oil-injection service: addresses crankcase-pressure fuel-pump Designs 1 and 2, WME carburetor repair and rejetting, enrichener and accelerator circuits, oil-pump synchronization, bleeding, output testing, and warning-system faults.
• Three-cylinder powerhead repair: covers removal, disassembly, cylinder inspection and honing, piston/rod and crankshaft work, check-valve Designs 1–3, reed blocks, thermostat service, torque sequences, and reassembly for bottom- and top-guided builds.
• Gear housing, midsection, and installation work: includes both water-pump designs, bearing-carrier and propeller-shaft service, pinion-depth and backlash setup, pressure testing, shock-absorber repair, Ride-Guide steering, cable adjustment, transom mounting, tiller-handle service, and Co-Pilot installation.
• Power-trim variants: separates Design I side-fill, Design II aft-fill, and single-ram systems, with electrical-versus-hydraulic diagnosis, flowcharts, pressure and leak-down tests, hydraulic repair, motor/pump service, purging, and sender/gauge checks.

Exact model and serial coverage

The three-cylinder group is identified as 1987–1993 production within U.S. serial numbers 0A996142 through 0D283221, Belgium 09502135 through 09793576, and Canada 0A722297 and above. The four-cylinder 100/115 group begins with 1988 production and covers U.S. 0B209468 through 0D283221, Belgium 09523034 through 09793576, and Canada 0A731673 and above.

The timing chapter separates 70/75/80 calibration data at the U.S. B239241/B239242, Belgium 9502134/9502135, and Canada A730006/A730007 serial breaks; the 75 Marathon/75XD and Model 90 have separate specification blocks. Three- and four-cylinder procedures are divided for timing-pointer alignment, carburetor and oil-pump synchronization, timing, throttle travel, and cable adjustment.

The opening section supplies model-specific engine weights, gear ratios, fuel/oil ratios, tank and gear-housing capacities, spark plugs, and firing orders. It also covers salt- and freshwater submersion recovery, an engine submerged while running, seasonal storage, detonation, and compression checks.

Diagnosis, specifications, and repair depth

The ignition section supplies primary-voltage readings at 300–1000 RPM and 1000–4000 RPM, resistance specifications for stators, triggers, and coils, and a test order for isolating the major ADI components. Charging coverage distinguishes rectifier-only and regulated arrangements, large-finned and small regulator/rectifier units, and 9-, 16-, and optional 24-amp systems. Starter repair runs from removal and armature testing through brush replacement, solenoid testing, reassembly, and installation.

Fuel-system material covers anti-siphon restriction checks, pump testing, check-valve service, and both pump designs. The WME carburetor chapter adds float and low-speed adjustment, setting tables, jet-orifice part-number charts, overhaul, variant-specific enrichener routing, and the four-cylinder acceleration-pump circuit. Oil-injection coverage includes hose routing, pump-drive inspection, bleeding, output and sensor tests, test-button and non-test-button warning systems, a wiring diagram, and troubleshooting charts.

The included three-cylinder powerhead section is equally specific. It documents flywheel and powerhead removal, internal disassembly, bore and piston inspection, honing, crankshaft and connecting-rod work, piston-ring installation, matched crankcase-cover assembly, torque patterns, and final installation. Several cautions matter during real repair work: the cylinder block and crankcase cover are a matched line-bored pair, and connecting-rod caps must return to the same rod in their original direction. During gear-housing installation, lubricant must not be left on top of the driveshaft; trapped grease can prevent full engagement, and tightening the housing can damage both the powerhead and gear housing. The oil-pump drive gears and O-rings also have to engage and seat correctly, since an assembly error can interrupt oil delivery and damage the powerhead.

Diagrams, tools, and PDF organization

Section 2D contains 12 wiring diagrams plus one Commander 2000 key/choke continuity test. Examples include the three-cylinder engine circuit with low-oil module, four-cylinder circuit with small regulator/rectifier, three-cylinder Commander 2000 power-trim circuit, tachometer/trim-indicator diagram, Commander 2000 start/trim/warning-horn circuit, and Commander side-mount remote-control diagram. Other illustrated references cover the oil-warning circuit, single-ram trim flowchart, powerhead assemblies, gear-housing components, swivel/transom brackets, and tiller/Co-Pilot hardware.

Named tool references include the Multi-Meter/DVA Tester 91-99750, Direct Voltage Adapter 91-89045, Dial Indicator Gauge Kit 91-58222A1, and Power Trim Test Gauge Kit 91-52915A3, plus model-specific gear-depth and backlash tooling. Factory data categories include component torque tables and sequences, carburetor settings and jet references, gear depth and backlash specifications, gear-housing pressure checks, trim-system pressure and leak-down tests, electrical resistance and voltage charts, capacities, lubricants, sealants, and inspection limits.

The 391-page set is divided into 17 PDF files: front matter, 3 pages; General Information and Specifications, 14; Electrical and Ignition, 68; Fuel System and Oil Injection, 41; three-cylinder Powerhead, 41; Lower Unit, 55; Power Trim, 117; and Installation/Attachments, 52.

Scope and safety note: electrical, fuel, oil-injection, timing, charging, wiring, power-trim, and installation sections support both three- and four-cylinder configurations. This PDF set contains Section 4A for internal three-cylinder powerhead repair; the separately listed factory Section 4B for four-cylinder powerhead repair is not included. Disconnect the battery before exposed-terminal work, ground ignition leads as directed, support the outboard before trim or midsection service, and isolate the spark-plug leads before propeller or gear-housing work.