🏷️ Basic Information

Make:

Jeep

Model:

Wrangler

Year:

1991

Chassis Code:

YJ

👋 Introduction

Segment:

Compact, body-on-frame SUV / Off-road vehicle.

Target Audience:

Enthusiasts, off-roaders, DIY mechanics, and professional technicians needing in-depth repair information for the 1991 Jeep Wrangler.

Competitors 1991:

Ford Bronco II, Chevrolet S-10 Blazer, GMC S-15 Jimmy, Toyota 4Runner, Nissan Pathfinder.

Vehicle Characteristics:

Renowned off-road capability, rugged design, removable doors and top, solid front axle (until 1986, but YJ era is leaf-sprung live axles), simple mechanicals.

Value:

Provides vehicle-specific, dealer-level repair and maintenance information, differentiating it from generic guides. Essential for accurate diagnostics and repairs, ensuring longevity and proper function of the vehicle.

📋 Manual Details

Coverage:

All Models & All Repairs A-Z

Pages:

Extensive (specific page count not provided in product info, but implied to be comprehensive)

Type:

Service and Repair Manual

Language:

English

Format:

Likely printed physical manual, potentially available in digital format (PDF) for sales purposes. The description emphasizes dealer technician use, suggesting a comprehensive print version.

📖 Manual Coverage

Engine Systems:

Engine mechanical (including cylinder head, block, pistons, crankshaft, camshaft), lubrication system, cooling system, fuel system (injection/carburetion), ignition system, exhaust system, emissions control systems.

Transmission Drivetrain:

Manual transmission, automatic transmission (if applicable), transfer case, drive axles, driveshafts, differentials, CV joints, U-joints.

Suspension Steering:

Front suspension (leaf springs, shocks, steering knuckles, ball joints), rear suspension (leaf springs, shocks, axle housing), steering system (steering gear, steering column, power steering pump and system if equipped), wheel alignment.

Brakes:

Front brake system (disc brakes, calipers, pads, rotors), rear brake system (drum brakes, wheel cylinders, brake shoes, drums), parking brake system, hydraulic system, ABS (if equipped).

Electrical Electronics:

12-volt battery system, charging system (alternator), starting system (starter motor), lighting system (headlights, taillights, interior lights), ignition system, instrument cluster, wiring diagrams, fuses, relays, power windows/locks (if equipped), radio/audio system.

Body Chassis:

Body construction, chassis frame, doors, hood, tailgate, interior trim, seats, convertible top mechanism, bumpers, exterior trim, corrosion protection.

HVAC:

Heating, Ventilation, and Air Conditioning (HVAC) system components, operation, diagnosis, and repair.

Maintenance Routine:

Oil changes, fluid checks and top-offs, filter replacements, lubrication, tire rotation, battery maintenance, spark plug replacement, belt inspection and replacement.

Diagnostics Troubleshooting:

Systematic diagnostic procedures for common and uncommon issues, symptom-based troubleshooting guides, diagnostic trouble codes (DTCs) and their meanings (if applicable to the OBD system of the era).

Repair Rebuild:

Detailed step-by-step instructions for component removal, disassembly, inspection, repair, reassembly, and installation for virtually all vehicle systems. Includes engine rebuilds, transmission overhauls, brake system repairs, etc.

Specifications Tolerances:

Precise torque specifications for fasteners, critical clearances, diagnostic data, fluid capacities, and dimensional tolerances required for proper assembly and operation.

Wiring Diagrams:

Comprehensive electrical wiring diagrams for all vehicle circuits, facilitating troubleshooting and repair of electrical issues.

Depth:

Comprehensive: Covers everything from basic scheduled maintenance to complete engine and transmission rebuilds, advanced electrical diagnostics, and body panel repair. Designed for professional technicians.

📊 Manual Specifications

Digital Format:

If sold digitally, typically PDF with searchable text and high-resolution images/diagrams.

Quality:

High quality, designed for frequent use in a workshop environment. Typically features clear diagrams, legible text, and durable printing.

Binding:

Likely a sturdy bound format (e.g., spiral bound, perfect bound) suitable for lying flat on a workbench.

Paper:

Durable paper stock to withstand workshop conditions and frequent handling.

⚙️ Engine Specifications

Engine Code 1:

4.0L Inline 6-Cylinder (242 ci)

Engine Description 1:

AMC 242, known for its torque and durability.

Displacement 1:

3956 cc (242 cubic inches)

Bore X Stroke 1:

3.875 in x 3.414 in (98.4 mm x 86.7 mm)

Compression Ratio 1:

8.8:1

Horsepower 1:

Approx. 177 hp @ 4700 rpm

Torque 1:

Approx. 220 lb-ft @ 3200 rpm

Engine Code 2:

2.5L Inline 4-Cylinder (150 ci)

Engine Description 2:

AMC 150, less common in later YJ models but available.

Displacement 2:

2466 cc (150 cubic inches)

Horsepower 2:

Approx. 121 hp @ 4800 rpm

Torque 2:

Approx. 170 lb-ft @ 2400 rpm

Fuel Delivery 4.0L:

Electronic Fuel Injection (EFI) - Renix or Chrysler MPI depending on specific production date within 1991, typically multipoint.

Fuel Delivery 2.5L:

Electronic Fuel Injection (EFI) - Renix or Chrysler MPI.

Ignition Type:

Distributorless Ignition System (DIS) or distributor-based ignition system, depending on specific engine and year updates.

Engine Oil Type:

API SG or higher; SAE 10W-30 is common for general use, consult manual for temperature-specific recommendations.

Coolant Type:

Conventional green ethylene glycol based antifreeze (50/50 mix with distilled water).

🔧 Transmission

Manual Transmission:

AX-5 5-speed manual (common with 2.5L and some 4.0L models)

Automatic Transmission:

AX-15 5-speed manual (common with 4.0L models)

Automatic Transmission Option:

TorqueFlite A999 3-speed automatic (less common in YJ era, more prevalent in earlier CJ models or specific export markets, but possible depending on build).

Transfer Case:

NP231 Command-Trac 2-speed part-time 4WD system with neutral position.

Manual Transmission Fluid:

GL-4 gear oil, SAE 75W-90 or 80W-90 recommended. Consult manual for exact specification.

Automatic Transmission Fluid:

ATF+3 or equivalent (if A999) or ATF+4 (later spec, but consult manual for specific 1991 requirement). AX-15 typically uses gear oil, not ATF.

📐 Dimensions

Wheelbase:

93.4 inches (2372 mm)

Length:

150.0 inches (3810 mm)

Width:

66.4 inches (1687 mm)

Height:

63.5 inches (1613 mm) (without options)

Curb Weight:

Approx. 3000-3400 lbs (1361-1542 kg), depending on engine and options.

Gross Vehicle Weight Rating Gvwr:

Approx. 4500-4700 lbs (2041-2132 kg)

🛡️ Safety Features

NHTSA Crash Test Ratings:

Information for 1991 models is not readily available for NHTSA 5-star ratings as testing protocols were different. Early YJs generally did not perform well in modern crash tests due to their design philosophy focused on off-road durability.

ABS:

Rear Anti-lock Braking System (RABS) was optional or standard on some models.

Seatbelts:

Three-point front seat belts, lap belts for rear passengers.

Roll Cage:

Integral roll cage structure for occupant protection, especially with the convertible top removed.

💡 Technology Features

Audio System:

Basic AM/FM radio, optional cassette player. Limited technological features by modern standards.

Cruise Control:

Optional on some models.

Onboard Diagnostics:

OBD-I (On-Board Diagnostics, First Generation) system with limited diagnostic codes accessible via specific procedures or diagnostic tools of the era.

🔧 Maintenance

Oil Change Interval:

Typically every 3,000 miles or 3 months, or as recommended by the manual based on driving conditions.

Tune Up Interval:

Spark plugs and air filter replacement typically around 30,000 miles, but consult manual for specific recommendations.

Transmission Fluid Change:

Manual: Every 60,000 miles. Automatic: Every 30,000-50,000 miles. Always consult the manual.

Transfer Case Fluid:

NP231 typically uses ATF+4 (or equivalent). Verify with manual.

Differential Fluid:

API GL-5 gear oil, SAE 80W-90 is common. Verify weight and type for front and rear differentials.

Brake Fluid Type:

DOT 3 or DOT 4 brake fluid.

Common Problems:

Leaf spring perches cracking, front sway bar disconnect (common modification), exhaust manifold cracks (4.0L), heater core leaks, rust (body and frame), radiator leaks, distributor drive gear wear (if applicable), C.U.P. system issues (if equipped).

Oil Filter Part Number:

Chrysler Part Number: 53007176 (for 4.0L engine), common aftermarket equivalents include Fram PH8A, Wix 51515, K&N HP-3001.

Air Filter Part Number:

Common aftermarket part number: Fram CA151, Wix WA10085.

📚 Vehicle History

Jeep Legacy:

Jeep has a long and storied history dating back to WWII, known for its ruggedness and off-road prowess. The Wrangler is the direct successor to the iconic CJ (Civilian Jeep) series.

Yj Generation:

The YJ generation (1987-1995) was a significant departure from the CJ-7, featuring rectangular headlights (a point of contention among purists), coil springs were replaced with leaf springs for both front and rear suspension, and a wider track.

Manufacturing Location:

Toledo, Ohio, USA.

Production Years Yj:

1987-1995.

🏆 Awards & Recognition

Off Road Accolades:

The Jeep Wrangler (YJ) is consistently recognized for its off-road capability and remains a popular choice for off-road enthusiasts and modifiers, even decades after its production.