🏷️ Basic Information

Make:

BMW

Model:

850i

Year:

1991

Chassis Code:

E31

Engine Code:

M70B50

👋 Introduction

Market Position:

The 1991 BMW 850i (E31) represented the pinnacle of BMW's luxury grand touring coupe offerings, positioned as a high-performance, technologically advanced, and exclusive vehicle. It competed against established luxury coupes from Mercedes-Benz (e.g., SEC models), Porsche (928), and Aston Martin.

Competitive Analysis:

The 850i stood out with its V12 engine, sleek aerodynamic design, and sophisticated chassis. While competitors offered powerful engines and luxurious interiors, the 850i was lauded for its engineering prowess, particularly its advanced electronics for the era and its unique styling that prioritized smooth airflow.

Key Features:

V12 engine, retractable headlamps, advanced electronic systems (e.g., automatic climate control, electronic throttle control), sophisticated suspension and braking, luxurious interior appointments, coupe body style.

📋 Manual Details

Coverage Areas:

Engine, Transmission, Drivetrain, Suspension, Steering, Brakes, Electrical System, Bodywork, HVAC, Fuel System, Cooling System, Exhaust System, Emissions Control, Maintenance, Diagnostics, Troubleshooting, Repair Procedures, Specifications

Page Count:

Extensive (Software format, likely containing thousands of pages equivalent)

Manual Type:

Service and Repair Manual Software

Language:

English

Format:

Software (Digital)

📖 Manual Coverage

Systems Covered:

Engine mechanical and electrical diagnostics, V12 engine specifics, automatic transmission (4HP24), SMG (optional for later models, but manual covers base), ABS, ASC+T (traction control), power steering, independent suspension (front and rear), disc brakes, electrical schematics, lighting, interior electronics, climate control, fuel injection, engine management (DME), emission controls, cooling system, lubrication, chassis and body repair, interior trim, SRS airbag system (if applicable to 1991 model year)

Procedures Included:

Scheduled maintenance, routine inspections, oil changes, filter replacements, tune-ups, engine component diagnostics and repair (e.g., ignition system, fuel system, valve adjustments), transmission service and repair, brake system overhaul, suspension and steering component replacement, electrical troubleshooting using schematics, climate control system servicing, body panel repair and adjustment, diagnostic trouble code (DTC) retrieval and interpretation, component testing procedures, torque specifications for all fasteners, alignment procedures, wiring diagram interpretation

Technical Depth:

Comprehensive from basic maintenance to complete engine and transmission rebuilds, advanced electrical diagnostics, and bodywork repair. Covers all aspects necessary for professional-level servicing and repairs.

📊 Manual Specifications

File Format:

Digital Software (Likely PDF or proprietary software for access)

Print Quality:

N/A (Digital format; content is clear and sharp)

Binding Type:

N/A (Digital format)

Paper Type:

N/A (Digital format)

⚙️ Engine Specifications

Engine:

M70B50

Engine Type:

60-degree V12

Displacement:

4988 cc (5.0 Liters)

Bore X Stroke:

84.0 mm x 75.0 mm

Compression Ratio:

8.8:1

Horsepower:

296 hp @ 5200 rpm (approx.)

Torque:

332 lb-ft @ 3900 rpm (approx.)

Fuel System:

Bosch Motronic M-1.3 Electronic Fuel Injection (EFI) with 12 individual throttle bodies

Fuel Type:

Premium Unleaded Gasoline (91 Octane or higher)

Spark Plugs:

12 x NGK BKR6EKPB (example, check manual for exact spec)

Oil Capacity:

7.9 Liters (8.4 US Quarts) - check manual for exact capacity and oil type

Coolant Capacity:

13.0 Liters (approx.)

Emission Systems:

Catalytic converters, EGR (Exhaust Gas Recirculation), secondary air injection system

🔧 Transmission

Transmission Type:

4-speed Automatic (ZF 4HP24)

Transmission Type:

6-speed Manual (Getrag 630G)

Transmission Features:

Electronic control for automatic transmission, lock-up torque converter, sport mode

Automatic Transmission Fluid Type:

BMW ATF LT 71141 or equivalent (e.g., Dexron III specification)

Automatic Transmission Fluid Capacity:

Approximately 8.0 Liters (check manual for exact capacity and refill procedure)

Manual Transmission Fluid Type:

BMW Synchromesh Fluid (e.g., SAE 75W-90 GL-4)

Manual Transmission Fluid Capacity:

Approximately 1.8 Liters (check manual for exact capacity)

📐 Dimensions

Length:

4,774 mm (187.9 inches)

Width:

1,855 mm (73.0 inches)

Height:

1,370 mm (53.9 inches)

Wheelbase:

2,672 mm (105.2 inches)

Curb Weight:

1,850 kg (4,079 lbs) approx. for automatic

Gross Vehicle Weight Rating:

2,300 kg (approx.)

Trunk Volume:

340 Liters (12.0 cu ft)

🛡️ Safety Features

Safety Ratings:

No specific NHTSA/Euro NCAP ratings available for this era, but designed to high BMW safety standards.

Active Safety Features:

Anti-lock Braking System (ABS), Automatic Stability Control and Traction (ASC+T), power-assisted steering, advanced chassis dynamics

Passive Safety Features:

Reinforced safety cell, crumple zones, driver and passenger airbags (standard for 1991 model year), 3-point seatbelts with pretensioners, impact-absorbing steering column

💡 Technology Features

Infotainment System:

Early BMW Business or Professional CD radios, potentially with optional CD changer. Analog climate control with digital display for temperature.

Driver Assistance Features:

ASC+T (Automatic Stability Control and Traction), cruise control, power tilt/telescope steering wheel with memory.

Connectivity Features:

Limited by era; primarily internal vehicle diagnostics and audio system.

Lighting Technology:

Aerodynamic retractable halogen headlights, rear fog lamps, integrated turn signals.

Engine Management System:

Bosch Motronic M-1.3 DME, featuring dual ECUs (one for each bank of cylinders) for precise V12 management.

🔧 Maintenance

Oil Change Interval:

Typically every 7,500-10,000 miles or 12 months (refer to manual for specific conditions and BMW's Condition Based Service system, if applicable).

Transmission Service Interval:

Automatic transmission fluid and filter replacement: typically every 30,000-60,000 miles (refer to manual for specific recommendations, as lifetime fluid was sometimes advertised but often benefits from periodic changes).

Coolant Flush Interval:

Every 2-4 years or 30,000-60,000 miles.

Brake Fluid Flush Interval:

Every 2 years, regardless of mileage.

Engine Oil Specification:

BMW Longlife-98 (LL-98) or equivalent synthetic oil, e.g., 5W-30 or 5W-40 (check manual for precise viscosity and API/ACEA ratings).

Coolant Specification:

BMW Antifreeze/Coolant (G48 ethylene glycol based) or equivalent (50/50 mix with distilled water).

Common Issues:

Cooling system leaks (radiator, hoses, water pump), VANOS (Variable Valve Timing) issues on later models (though M70 does not have VANOS), EML (Electronic Motor Control) issues, ignition coil failure, ABS/ASC sensor failures, dashboard pixelation (LCD displays), headlight motor failure, window regulator issues, general aging of rubber and plastic components, fuel pump failures, transmission control unit problems.

Preventative Maintenance:

Regular inspection of cooling system, proactive replacement of aging hoses and belts, ensuring proper ventilation for electronics, regular battery maintenance, attention to any warning lights.

📚 Vehicle History

Brand Heritage:

BMW (Bayerische Motoren Werke AG) has a long-standing reputation for building performance-oriented luxury vehicles with a focus on driving dynamics and engineering excellence.

Model Evolution:

The 8 Series (E31) was a completely new platform for BMW, representing a departure from previous coupe designs. It was intended to be a flagship model, showcasing BMW's technological capabilities. The 850i was the initial V12 model, later joined by the V8-powered 840i.

Production Years:

1989-1999

Manufacturing Location:

Dingolfing, Germany

🏆 Awards & Recognition

Recognitions:

While specific awards for the 1991 model year might be scarce, the E31 8 Series was widely praised for its design and engineering upon release, often cited as a benchmark for automotive styling and V12 performance.

Ratings:

Consistently rated highly by automotive journalists for its performance, comfort, and luxurious grand touring capabilities.

📄 Wheels And Tires

Standard Wheel Size:

17 x 7.5J (front), 17 x 8.0J (rear) - Style 32 alloy wheels

Standard Tire Size:

235/45 ZR17 (front), 255/40 ZR17 (rear)

Wheel Bolt Pattern:

5x120

📄 Brakes

Front Brake Type:

Vented Discs

Front Brake Diameter:

302 mm (approx.)

Rear Brake Type:

Solid Discs

Rear Brake Diameter:

300 mm (approx.)

Brake System:

Hydraulic, power-assisted with ABS

📄 Steering

Steering Type:

Recirculating ball, hydraulic power assisted

Steering Features:

Speed-sensitive power assistance, tilt and telescoping steering column