OMC Cobra Sterndrive 1990 Service Manual (P/N 507878)

The 1990 OMC Cobra Stern Drive Service Manual from Outboard Marine Corporation (P/N 507878) covers the 2.3L, 3.0L, 3.0L HO, 4.3L, 4.3L HO, 5.0L, 5.0L HO, 5.7L, and 5.8L engine packages. Use the package identification chart to match the engine model to its vertical drive and transom mount before choosing a repair procedure.

Printable Manual and Wiring PDFs

Finding procedures and reading diagrams: Both PDFs have fixed page images, so use the printed section contents and page numbers to navigate. Neither file has text search or PDF bookmarks. Zoom in to read small connector labels and wire callouts in the color wiring diagrams. Some callout numbers in the workshop PDF's electrical legends are faint.

The ZIP download contains two printable PDFs with 618 pages total: the 608-page service manual and a 10-page wiring file containing four color diagrams, their accompanying reference pages, two repeated pages, and one blank reverse side. The repeated and blank pages are included in the total.

Cobra Sterndrive, Engine, and Control Repairs

These selected service topics illustrate the manual's coverage. The service information also includes submerged-engine procedures and break-in checks.

• Transom and gimbal: Exhaust and U-joint bellows, gimbal and pivot bearings, water passages, hydraulic manifolds, and shift-cable installation.
• Upper and lower drive: U-joint and water-pump service, standard- and counter-rotation gearcases, bearing carriers, gear shimming, backlash, rolling torque, and leak testing.
• Engine service: Model-specific internal repairs, engine and drive removal and installation, coupler and rear mount service, and engine-to-drive alignment.
• Electrical diagnosis: Battery, charging, and cranking circuits, ignition and Electronic Shift Assist (ESA) testing, and model-specific wiring diagrams.
• Fuel and cooling: Carburetor overhaul and adjustment, fuel-pump pressure and vacuum tests, cooling fault isolation, and engine-specific water-flow diagrams.
• Trim, steering, and controls: Trim/tilt hydraulic testing and bleeding, power-steering pump and cylinder service, remote-control repair, and shift-cable adjustment.

The manual is suited to marine technicians and owners experienced in sterndrive repair. Its package chart links the installed drive to the applicable service information, and its diagnostic charts help narrow a fault before teardown.

Engine Repair Scope

3.0L, 4.3L, 4.3L HO, and 5.7L: The engine sections cover cylinder heads and valves, camshafts and bearings, crankshafts, main and connecting rod bearings, block inspection, pistons and rings, oil pumps, and timing components. The 4.3L, 4.3L HO, and 5.7L section refers to the applicable Chevrolet Engine Service Manual for additional operations.

2.3L: Coverage includes timing belt and timing checks, manifolds, oil pan and pump, rear seal, rocker arms and lash adjusters, valve clearance, water pump, compression and cam-lobe checks, and PCV service. For procedures outside this section, OMC refers to the separate Ford Power Products Service Manual, P/N 194-216.

5.0L, 5.0L HO, and 5.8L: Marine service covers core plugs, rear seal, manifolds and exhaust, mounts, oil pan and pump, valve train, water pump, and compression checks. For a full block overhaul, additional engine documentation is needed.

Ignition, Wiring, and Carburetor Diagnosis

The electrical section covers circuit protection, sending units, firing order, and ignition-specific tests. The 4.3L HO Spitfire coverage identifies the timing and knock sensors, coil pack, and ignition module. The color wiring file shows engine harnesses for the 2.3L/5.0L/5.0L HO/5.8L group, the 3.0L/3.0L HO PWS group, and the 4.3L HO, plus the instrument harness shared by all models.

The fuel section separates Rochester two-barrel service for 3.0L PWC packages from Holley two-barrel service for 2.3L, 3.0L, 3.0L HO, 4.3L, 5.0L, and 5.0L HO PWS packages. Holley four-barrel coverage is divided between 5.7L PWS and 4.3L HO/5.8L PWS applications. Diagnostic charts distinguish boat-side fuel delivery faults from engine and carburetor problems.

Drive Setup, Propellers, and Shift Faults

The drive chapters distinguish standard- and counter-rotation lower units and cover pinion and driveshaft shimming, shift-rod setup, propeller shaft and gear service, and pressure and vacuum checks. Assembly cautions address bearing-carrier orientation, damage to retainer threads, and the risk of forward engagement failure from a reversed counter-rotation clutch dog. Propeller coverage includes application charts, test wheels, removal and installation, and hub replacement.

The trim/tilt schematics show circuit behavior in normal trim and tilt, shallow-water and reverse operation, and relief, impact, manual-release, and thermal-expansion conditions. The steering section includes hose and cable service, leak checks, and air purging. The controls section distinguishes hard shifting, ignition interruption, and jumping out of gear, with tests for the ESA interrupter and overstroke switches.

Named shop tools include the OMC Vacuum Tester P/N 390954, Trim/Tilt In-Line Pressure Tester P/N 983977, Shift Rod Height Gauge P/N 912277, Bellcrank Alignment Plate P/N 914017, and Shim Gauge Kit P/N 984329. The manual opens with a marine service safety section.

Drive Ratios and Compression Test Limits

The drive identification chart lists overall ratios of 2.00:1 for 2.3L, 1.86:1 for 3.0L and 3.0L HO, 1.68:1 for 4.3L and 4.3L HO, 1.59:1 for 5.0L and 5.0L HO, and 1.41:1 for 5.7L and 5.8L.

For the warm-engine compression test at wide-open throttle, the manual uses 75% of the highest cylinder reading as the lower limit. Its quick-reference chart gives the corresponding minimum readings for comparison across cylinders.