🏷️ Basic Information

Make:

Porsche

Model:

928 S4-GT

Model Code:

928

Generation:

Third Generation (928 S4/GT)

Specific Variant:

S4-GT

👋 Introduction

Positioning:

The Porsche 928 represented a significant departure for Porsche, aiming to be a premium grand tourer with a front-engine, V8 configuration, a departure from their traditional rear-engine sports cars. The S4 and GT variants refined this concept with increased power and luxury.

Competitors:

Competed against high-end GT cars like the Jaguar XJS, Aston Martin Vantage, and certain BMW models of the era. Its unique transaxle design and V8 engine offered a different driving experience.

Gran Touring:

Designed for comfortable high-speed cruising over long distances, combining performance with luxury.

Transaxle Design:

Rear-mounted transaxle for optimal weight distribution, contributing to superior handling characteristics.

V8 Engine:

The powerful 32-valve V8 engine was a hallmark of the 928, offering smooth acceleration and a distinctive sound.

Aerodynamics:

Sleek, aerodynamic styling with pop-up headlights, characteristic of Porsche design language of the period.

📋 Manual Details

Primary Focus:

Electrical System Diagnostics and Repair

Secondary Focus:

Electrical Component Troubleshooting, Wiring Harness Repair, Fuse and Relay Identification

Estimated Pages:

Detailed wiring diagrams suggest a substantial page count, likely exceeding 150 pages for comprehensive coverage of the electrical system.

Type:

Wiring Diagram Manual / Electrical Troubleshooting Manual

Language:

English (implied by common workshop manuals for this era and market).

Format:

Likely a printable document or PDF. The description emphasizes diagrams and illustrations, consistent with technical manuals.

📖 Manual Coverage

Power Distribution:

Battery, Alternator, Starter, Charging System, Fuse Boxes, Power Distribution Modules.

Ignition System:

Ignition Control Unit (DME), Ignition Coils, Spark Plug Wires, Sensors related to ignition timing.

Fuel System:

Fuel Pump, Fuel Injectors, Fuel Pressure Regulator, Engine Control Unit (DME) inputs/outputs related to fuel delivery.

Engine Management:

DME control unit, sensors (e.g., MAF, TPS, Knock, O2), actuators, wiring to engine components.

Lighting:

Headlights (low/high beam), Taillights, Brake Lights, Turn Signals, Interior Lighting, Fog Lights.

Instrumentation:

Dashboard Gauges (Speedometer, Tachometer, Fuel, Temp), Warning Lights, OBC (On-Board Computer) connections.

Comfort Controls:

HVAC (Heater, Ventilation, Air Conditioning) blower, climate control panel, seat heating, power windows, mirrors, central locking.

Audio And Accessories:

Radio/Stereo system, amplifier, speakers, power antenna, cigarette lighter/power outlets, sunroof controls.

Braking System:

ABS (Anti-lock Braking System) sensors and control module, brake fluid level sensor.

Chassis Electronics:

Cruise Control System, Immobilizer/Alarm System (if applicable).

Troubleshooting:

Step-by-step diagnostic procedures for electrical faults, identifying open circuits, short circuits, and ground issues.

Repair:

Instructions for repairing damaged wiring, replacing connectors, fuses, relays, and electrical components.

Component Testing:

Guidance on testing the functionality of various electrical components using multimeters and other diagnostic tools.

Wiring Diagram Interpretation:

Detailed explanations of how to read and understand complex wiring schematics, including wire colors, pinouts, and component locations.

Depth:

Comprehensive. This manual provides the detailed schematic level information required for in-depth electrical diagnosis and repair, suitable for both professional technicians and advanced DIY enthusiasts with basic electronic knowledge.

📊 Manual Specifications

Format Type:

Likely PDF or scanned original document.

Searchability:

If PDF, may be text-searchable depending on creation method. Scanned documents may require OCR for searchability.

Quality:

Dependent on the source. Original factory manuals are typically high-quality prints. Digital reproductions may vary.

Binding:

N/A (for digital format). If printed, likely perfect bound or spiral bound for ease of use in a workshop.

Paper:

N/A (for digital format). Original manuals used durable paper stock for workshop environments.

⚙️ Engine Specifications

Type:

V8, naturally aspirated

Displacement:

4.7 Liters (4664 cc) for S4, 5.0 Liters (4957 cc) for GT

Bore X Stroke:

S4: 94.0 mm x 84.5 mm; GT: 94.0 mm x 88.0 mm

Compression Ratio:

S4: 10.0:1; GT: 10.4:1

Valvetrain:

DOHC, 4 valves per cylinder

Horsepower:

S4: ~316 hp (235 kW) at 5500 rpm; GT: ~326 hp (243 kW) at 6000 rpm

Torque:

S4: ~315 lb-ft (427 Nm) at 3000 rpm; GT: ~339 lb-ft (460 Nm) at 4500 rpm

Injection:

Bosch DME (Digital Motor Electronics) with L-Jetronic or similar sequential fuel injection

Fuel Type:

Unleaded Premium Gasoline

Fuel Pump:

Dual electric fuel pumps (common for reliability in this model)

ECU:

Porsche DME control unit

🔧 Transmission

Type:

5-speed Manual Transaxle (M28/45 for S4, M28/46 for GT)

Type:

4-speed Automatic Transaxle (Tiptronic available on later models, though not explicitly mentioned for S4/GT by this manual)

Gear Ratios:

Specific gear ratios vary by transmission and market, but are designed for strong acceleration and comfortable highway cruising.

Fluid Type:

Typically SAE 75W-90 synthetic gear oil, specific Porsche A-number may apply.

Type:

Hydraulically actuated single dry plate clutch (for manual transmission).

📐 Dimensions

Length:

Approx. 4,655 mm (183.3 in)

Width:

Approx. 1,775 mm (69.9 in)

Height:

Approx. 1,280 mm (50.4 in)

Wheelbase:

Approx. 2,500 mm (98.4 in)

Curb Weight:

Approx. 1,600 - 1,750 kg (3,527 - 3,858 lbs) depending on transmission and equipment.

Gross Weight:

Typically around 2,100 kg (4,630 lbs).

Rear Luggage Space:

The 928 featured a hatchback design, offering decent cargo space for a sports car, with rear seats that could be folded down for more utility.

🛡️ Safety Features

Crash Test Results:

While formal crash test ratings (like NHTSA or Euro NCAP) were less standardized during its production period, Porsche vehicles of this era were engineered with robust safety structures.

ABS:

Standard Anti-lock Braking System (ABS) for enhanced braking control.

Traction Control:

Limited-slip differential (LSD) was standard or optional on many models, enhancing traction.

Airbags:

Driver's side airbag was introduced during the S4/GT production run.

Seatbelts:

Three-point inertia-reel seatbelts with pretensioners.

Body Structure:

Reinforced passenger cell and crumple zones.

💡 Technology Features

Audio System:

Original Porsche branded radio/cassette decks, often with optional amplifiers and premium speaker systems. Aftermarket head units are common upgrades.

Climate Control:

Automatic climate control system with electronic sensors and actuators for precise temperature regulation.

Cruise Control:

Standard cruise control system for highway driving.

Early Electronics:

The 928 S4/GT featured early iterations of integrated electronic systems for engine management, climate control, and ABS, reflecting the technological advancements of the late 1980s and early 1990s.

🔧 Maintenance

Oil Change:

Typically every 5,000 - 7,500 miles or annually, using high-quality synthetic oil.

Timing Belt:

Crucial for the V8 engine. Replacement interval is critical, often recommended every 30,000 - 50,000 miles or every few years due to age, as failure can cause catastrophic engine damage.

Coolant Flush:

Every 2-3 years or as per manufacturer recommendation to maintain cooling efficiency.

Engine Oil:

Porsche A40 or similar API SN/SP, ACEA C3 or C4 specification synthetic oil, typically 5W-40 or 0W-40. Check manual for exact Porsche approval number (e.g., A40, C30).

Brake Fluid:

DOT 4 or DOT 5.1 high-temperature brake fluid, replaced every 2 years.

Power Steering Fluid:

Specific hydraulic fluid, typically Pentosin CHF 11S or equivalent, check manual for exact specification.

Transmission Fluid:

Manual: SAE 75W-90 Synthetic Gear Oil. Automatic: Specific ATF fluid approved by Porsche for the transmission type.

Electrical Gremlins:

Aging wiring insulation, corroded connectors, failing relays and fuses are common, making this wiring diagram manual invaluable.

Fuel System Issues:

Leaking fuel lines, worn fuel pump seals, and clogged injectors can occur.

Cooling System Issues:

Radiator leaks, hoses degradation, and water pump failures are also common with age.

Suspension Components:

Worn control arm bushings, ball joints, and rear trailing arm bushings can impact handling and ride comfort.

📚 Vehicle History

Porsche Legacy:

Porsche, renowned for its rear-engine sports cars like the 911, sought to diversify its lineup with a front-engine, V8-powered grand tourer.

928 Development:

The 928 was initially conceived in the 1970s as a potential 911 successor, evolving through various iterations including the 928 S, S2, S3, S4, and the GT. The S4 and GT represented the pinnacle of its development.

S4 Introduction:

The 928 S4 was introduced for the 1987 model year, featuring significant updates including a larger engine, improved aerodynamics, and a revised interior.

Gt Introduction:

The 928 GT was introduced in 1989 as a more performance-oriented version of the S4, featuring a larger displacement engine and sportier suspension tuning.

Production Years:

The Porsche 928 was produced from 1978 to 1995. The S4 variant ran from 1987 to 1991, and the GT from 1989 to 1991.

Manufacturing Location:

Stuttgart, Germany.

🏆 Awards & Recognition

Automotive Excellence:

While specific awards for the S4/GT model might be less documented than for earlier versions, the 928 platform was widely recognized for its engineering innovation, performance, and comfort as a premium grand tourer.

Performance Reviews:

Contemporary reviews praised its powerful V8 engine, sophisticated handling due to its transaxle layout, and luxurious interior for long-distance travel.

Engineering Accolades:

The Porsche 928 as a whole received accolades for its design and engineering, including being named Motor Trend's Car of the Year for 1978, setting a precedent for its continued development into the S4 and GT.