1986 Mercedes Benz 420SEL Repair Manual

The 1986 Mercedes Benz 420SEL is a luxury sedan featuring a 4.2L V8 engine, advanced suspension system, and comprehensive electronic controls. This repair manual covers essential maintenance procedures, troubleshooting guides, and technical specifications for proper servicing and repair of all major components including engine, transmission, brakes, electrical systems, and bodywork.

1. Vehicle Specifications 2. Engine System 3. Transmission & Drivetrain 4. Braking System 5. Suspension & Steering 6. Electrical System 7. Fuel System 8. Cooling System 9. Body & Interior 10. Maintenance Schedule 11. Troubleshooting

Vehicle Specifications

Technical data and general information for the 1986 Mercedes Benz 420SEL.

Specification	Description
Engine Type	4.2L V8 M116/M117 gasoline engine
Displacement	4196 cc
Power Output	201 hp @ 5200 rpm
Torque	228 lb-ft @ 3500 rpm
Transmission	4-speed automatic
Fuel System	CIS-E electronic fuel injection
Brakes	Four-wheel disc brakes with ABS
Suspension	Independent front and rear with self-leveling
Wheelbase	121.1 inches
Curb Weight	3,880 lbs

Engine System

Comprehensive engine maintenance and repair procedures.

Engine removal and installation: Disconnect battery, drain fluids, remove accessories.
Valve adjustment: Set clearances to 0.006-0.008 inches cold.
Timing chain replacement: Align timing marks during installation.
Ignition system: Distributor cap, rotor, spark plugs (gap 0.028 inches).

WARNING! Engine components are heavy; use proper lifting equipment. Allow engine to cool before servicing.

Transmission & Drivetrain

Automatic transmission service and drivetrain components.

Transmission fluid change: Use Dexron II ATF, capacity 7.5 quarts.
Transmission removal: Support engine, disconnect driveshaft and linkages.
Differential service: Check fluid level and condition regularly.
Driveshaft inspection: Check U-joints for wear and proper lubrication.

CAUTION! Use proper transmission jack for removal. Secure vehicle on lift stands.

Braking System

Brake Pads: Front and rear pad replacement procedures.
Rotors: Minimum thickness specifications and resurfacing limits.
Brake Fluid: DOT 4 fluid, bleeding procedure for ABS system.
Calipers: Inspection and rebuilding guidelines.
Parking Brake: Cable adjustment and shoe replacement.
ABS Components: Sensor testing and control module diagnostics.
Master Cylinder: Bench bleeding and installation.
Brake Lines: Inspection for corrosion and proper routing.

Suspension & Steering

Front and rear suspension components with self-leveling system.

Front Suspension: Control arms, ball joints, struts, sway bar links. Rear Suspension: Trailing arms, self-leveling shocks, springs. Steering: Power steering pump, gearbox, tie rods. Self-leveling system: Hydraulic pump, accumulators, height control valve.

Electrical System

Wiring diagrams, component locations, and electrical troubleshooting.

Battery: 12V 80Ah, located in engine compartment.
Alternator: 90A output, voltage regulator testing procedures.
Starter: Solenoid testing and replacement guidelines.
Fuses & Relays: Location and amperage specifications.

Tip: Disconnect battery before electrical work to prevent short circuits.

Fuel System

CIS-E continuous injection system maintenance and repair.

Fuel pump: Electric in-tank pump, pressure testing (65-75 psi).
Fuel filter: Replace every 30,000 miles.
Injectors: Cleaning and flow testing procedures.
Air flow sensor: Plate movement and control pressure adjustments.
Cold start valve: Operation testing and replacement.
Fuel accumulator: Maintains system pressure after shutdown.
Warm-up regulator: Electronic control for mixture enrichment.
Fuel lines: Inspection for leaks and proper routing.

WARNING! Relieve fuel pressure before servicing. No smoking or open flames near fuel system.

Cooling System

Radiator, thermostat, water pump, and cooling fan maintenance.

Body & Interior

Body panel alignment, door adjustments, interior trim, and electrical accessories.

CAUTION! Use proper trim removal tools to avoid damage to plastic components.

Maintenance Schedule

Recommended service intervals and procedures.

Service Interval	Maintenance Items	Notes
Every 3,000 miles	Oil and filter change	Use 10W-40 motor oil
Every 7,500 miles	Tire rotation	Check alignment
Every 15,000 miles	Air filter replacement	Check fuel filter
Every 30,000 miles	Spark plugs	Gap 0.028 inches
Every 60,000 miles	Timing chain	Inspect for wear
Every 2 years	Brake fluid flush	DOT 4 fluid
Every 3 years	Coolant replacement	50/50 mixture

Troubleshooting

Symptom	Possible Cause	Corrective Action
Engine won't start	Fuel pump, ignition, battery	Check fuel pressure, spark, battery voltage.
Rough idle	Vacuum leaks, dirty injectors	Inspect vacuum hoses, clean injectors.
Transmission slipping	Low fluid, worn bands	Check fluid level and condition.
Brake pulsation	Warped rotors	Resurface or replace rotors.
Electrical issues	Bad grounds, alternator	Check ground connections, test alternator output.

Reset: Clear fault codes using appropriate diagnostic tools.

Service: Contact authorized Mercedes-Benz service center for complex diagnostics.