Positioning:
The 2006 Impreza WRX STi represents the pinnacle of Subaru's rally-bred performance sedan for that era, offering a blend of everyday usability and track-ready capability.
Competitors:
Competed against performance variants of the Mitsubishi Lancer Evolution, Subaru Legacy GT, Ford Focus RS, and Volkswagen Golf R.
Performance Focus:
Iconic symmetrical all-wheel drive system, turbocharged Boxer engine, DCCD (Driver Controlled Center Differential), performance braking system.
Handling:
Tuned suspension for aggressive driving, responsive steering, and balanced chassis dynamics.
Engine:
2.5L EJ257 Turbocharged Boxer Engine, including maintenance, diagnosis, disassembly, and assembly procedures.
Transmission:
6-speed manual transmission (TY856WB2CA), including clutch system, driveline, differentials (front, center, rear).
Brakes:
Front Brembo 4-piston calipers, rear 2-piston calipers, ABS, EBD, and brake system diagnostics.
Suspension:
Front MacPherson struts, rear double wishbone, adjustable ride height and damping systems, alignment specifications.
Electrical:
Full wiring diagrams, ECU pinouts, sensor testing, charging system, starting system, lighting, comfort systems, power accessories.
Chassis Body:
Body and frame structure, doors, hood, trunk, glass, exterior trim, interior trim, HVAC, SRS (airbag) system.
Fuel System:
Fuel tank, fuel pump, injectors, fuel pressure regulation, emissions control system (EVAP).
Cooling System:
Radiator, thermostat, water pump, cooling fan operation, coolant specifications.
Exhaust System:
Exhaust manifold, catalytic converter, mufflers, performance considerations.
Maintenance:
Routine service checks, oil and filter changes, spark plug replacement, fluid checks and top-offs, belt inspections and replacement.
Troubleshooting:
Diagnostic trouble codes (DTCs), symptom-based diagnostics for engine, transmission, electrical, and HVAC systems.
Repair:
Engine component replacement (pistons, rods, bearings, valves), turbocharger overhaul, transmission rebuilds, brake caliper replacement, suspension component replacement.
Diagnostics:
OBD-II diagnostic procedures, live data analysis, specialized Subaru diagnostic tools (e.g., Subaru Select Monitor).
Timing:
Timing belt replacement (on earlier EJ20/EJ25, though EJ257 often uses a timing chain/belt hybrid system depending on variant, manual clarifies specific setup), camshaft and crankshaft timing.
Calibration:
ECU reprogramming, idle air control valve (IACV) learning, throttle position sensor (TPS) calibration.
Depth:
Comprehensive from basic maintenance to full engine and transmission overhaul, including detailed torque specifications and assembly sequences.
Engine Type:
2.5L (2457cc) DOHC 16-valve turbocharged horizontally-opposed (Boxer) 4-cylinder engine.
Horsepower:
300 hp @ 6000 rpm (SAE Net)
Torque:
290 lb-ft @ 4000 rpm (SAE Net)
Injection Type:
Multi-point fuel injection (MPI) with Denso side-feed fuel injectors.
Turbocharger:
IHI VF37 twin-scroll turbocharger.
Intercooler:
Top-mounted air-to-air intercooler.
Fuel Requirement:
Premium Unleaded Gasoline (91 octane or higher recommended).
Oil Change:
Every 3,000-5,000 miles or 6 months, whichever comes first, especially under hard driving conditions. Synthetic oil recommended.
Spark Plugs:
Typically 30,000 miles for Iridium spark plugs (check manual for specific PN).
Timing Belt:
For EJ257 engines that utilize a belt, typically 105,000 miles or 7 years. Critical item; manual provides exact procedure and tensioning specs.
Brake Fluid:
Every 2 years or 30,000 miles.
Engine Oil:
SAE 5W-30 Synthetic (API SN/SP or ILSAC GF-6) - Check manual for exact PN and capacity (approx. 5.0 quarts).
Transmission Fluid:
Subaru Genuine Manual Transmission Fluid (API GL-5) or equivalent. Capacity approx. 2.7 liters.
Differential Fluid Front:
Subaru Genuine Differential Gear Oil (API GL-5) or equivalent. Capacity approx. 1.0 liter.
Differential Fluid Rear:
Subaru Genuine Differential Gear Oil (API GL-5) or equivalent. Capacity approx. 1.2 liters.
Coolant:
Subaru Super Coolant (Blue) or equivalent. Capacity approx. 7.7 liters.
Piston Slap:
Some EJ257 engines may exhibit piston slap, particularly on cold starts. Manual provides diagnostics for this.
Ring Land Failure:
Can occur due to detonation/pre-ignition. Proper fuel, tuning, and maintenance are crucial. Manual details engine build and component tolerances.
Clutch Wear:
High-performance nature can lead to accelerated clutch wear with aggressive driving. Manual outlines clutch inspection and replacement.
Turbocharger Failure:
Can be caused by oil starvation or debris. Manual provides maintenance procedures and troubleshooting for the IHI VF37 turbo.
