# Overview

Impreza WRX and WRX STI (09/1998 — 09/2000)
Legacy B4 RSK and GT (06/1998 — 04/2001)
Forester S, S/tb, T/tb, STI (09/1998 — 01/2002)

These models use a 32-bit ECU made by Unisia Jecs Corporation. It is similar internally to the USDM 32-bit ECU made by Automotive Electronic Control Systems Inc. and shares many sensors and actuators.

Some notable features of this ECU include:

  • Hitachi MAF sensor with 300+ g/s airflow range
  • 2.8 bar MAP sensor
  • Closed-loop boost control
  • Knock detection with digital signal processing. Configurable sensitivity for odd and even cylinder banks
  • Ignition system
    • Single turbo engines have a wasted-spark coil pack with spark plug wires
    • Twin Turbo engines have 4 coils directly on the spark plugs

# Impreza

# WRX and WRX STI (09/1998 — 09/2000)

These cars come with either an EJ207 or an EJ205 if you have the WRX GF8.

The STI EJ207 is an 8.0:1 compression engine. WRX EJ207's are mechanically the same as the STI model but the ECU is de-tuned to deliver lower boost and torque than the STI.

The EJ205 is the same 9.0:1 compression engine used in the JDM SF5 Forester turbo models.

# Legacy

# B4 RSK and GT (06/1998 — 04/2001)

These cars come with either the twin-turbo EJ206 (GT) or EJ208 (RSK) engine. EJ206s come with a 4-speed automatic transmission and are tuned for lower boost and power than the EJ208 with a lower rev limit. The Revision A and B models of the EJ206 had a 8.5:1 compression ratio vs 9.0:1 for all other models of EJ206 and EJ208.

The sequential turbo system usually operates in primary mode, relying on the primary turbo to supply boost. Above 4000 rpm, the ECU will use both turbos simultaneously when conditions are right. This allows for a larger combined exhaust housing cross-sectionally area without giving up lower RPM turbo response. However, the transition from primary to secondary mode causes a momentary drop in torque. The magnitude and duration of this drop can be reduced with engine modifications and ECU tuning.

# Forester

# S, S/tb, T/tb, STI (09/1998 — 01/2002)

The JDM Forester comes with a 9.0:1 compression EJ205. Contrary to popular belief, the EJ205 in the STI model is exactly the same as the other SF5 turbo models. It also shares the same ECU part number and tune.

# Reliabilty and Common Issues

# ECU Tuning

The main cause of problems for these cars is fuel octane. The JDM ECU is tuned for JDM fuel, which has a 98-100 RON octane rating vs Canadian 91/94 AKI (~95 - 98 RON). The lower octane range and engine condition usually result in detonation, which sounds like a crackle or metallic rattle from the engine bay under medium to heavy throttle.

projectLAMBDA has tunes for these ECUs to work properly on either 91 or 94 octane Canadian gas. Our tune will also increase the knock sensitivity of the ECU so that it can respond quickly to detonation before any damage occurs.

# Ignition System

# Single Turbo - EJ205, EJ207

A very high percentage of these JDM engines have misfire issues under boost caused by old spark plug wires. If you still have the original wires, replacement is mandatory before tuning.

# Twin Turbo - EJ206, EJ208

The twin turbo engines received a coil-on-plug ignition system. This is a reliable configuration which needs little maintenance.

Revision C engines received upgraded coils which can be identified by their grey plastic housing. These coils can handle higher dwell times than the earlier black coils and can be retrofitted to Revisions A and B along with increasing dwell time in the tune.


Recommended spark plug is NGK BKR7EIX at 0.8mm gap.

# MAF sensor

A high percentage of these cars still have the original 20+ year old MAF sensor. They usually fail at higher airflow first by reading 10%+ too lean, which causes the ECU to run leaner fuel mixtures and higher spark timing. This leads to detonation and is the 2nd leading cause of damaged engine bearings on these cars.


MAF sensor failure will not trigger the engine light but can be detected manually by data logging.

# Oxygen Sensor

These ECUs do not have any OBD2 capability and cannot reliably detect a failing O2 sensor unless the circuit itself has failed. The ECU will overcompensate for a bad O2 sensor by adding up to 25% extra fuel, resulting in poor fuel economy. This can be checked easily by datalogging the ECU.

# Upgrades

# Fuel Pump

OEM 440cc injectors will max out the fuel pump above 85% duty cycle. Upgrading the fuel pump will allow you to run higher boost at high RPM without running out of fuel.

# 3-port wastegate solenoid

The stock 2-port solenoid limits how fast the turbo can spool. Using a 3-port solenoid in interrupt mode will help the turbo spool faster and reach higher peak boost.

# Exhaust Upgrades

Exhaust upgrades can include: catback exhaust, high flow downpipe(s), aftermarket header. Lower exhaust back-pressure gives you faster spool, higher peak power potential and lower EGT. Tuning may be required to maintain stable boost.

# Cold Air Intake

Aftermarket cone filters that bolt directly onto the MAF are not recommended. This sucks hot air from the engine bay reducing the engine’s knock resistance and reduces the max airflow that the MAF can read. MAF sensors also don’t seem to last as long with the cone filter.


Changes to the air intake will change the MAF sensor's calibration. Remember to update the tune and verify fuel ratio before applying heavy loads to the engine.

# Turbo

Larger aftermarket turbos are also available and will require bigger injectors. Intercooler and turbo inlet upgrades are also recommended to handle the higher boost.

# Twin-Turbo Upgrades

# Hose 10 Mod

The factory turbo control system has the wastegate solenoid bleed tied to the bypass valve pressure signal. This gives the turbo a smooth but laggy boost response and limits maximum boost to around 1.0 bar of boost.

The hose 10 mod removes this coupling and allows boost to exceed this mechanical 1.0 bar boost limit and allows faster turbo spool (recommended only with tuned ECU).


Do not use this mod without a tune! The engine load created by higher boost will be outside the range of the stock fuel and spark maps.

# Single Turbo Swap

Later spool, but smoother and increased torque/boost curve. Depending on turbo size, power can also be increased. The Legacy ECU should be re-used and reflashed with a single turbo tune to avoid having to make changes to the wiring harness.

# Specifications

# Chassis Codes

Model Revision Production Dates Changes
Impreza GC8F/GF8F 09/1998 — 09/1999 Initial release
Impreza GC8G/GF8G 09/1999 — 09/2000 Turbo changed to VF29
Legacy BE5A/BH5A 06/1998 — 04/1999 Initial release
Legacy BE5B/BH5B 05/1999 — 04/2000 No change
Legacy BE5C/BH5C 05/2000 — 04/2001 Upgraded ignition coils, VF31/VF32 turbos
Forester SF5B 09/1998 — 12/1999 Initial release
Forester SF5C 01/2000 — 12/2000 No change
Forester SF5D 01/2001 — 01/2002 No change

# Engine Specifications

Chassis Code Body Trim Engine Power* Torque* Rev Limit
GC8 Sedan WRX EJ207 276 bhp @ 6500 rpm 250 lb-ft @ 4000 rpm 7600
GC8 Sedan, Coupe WRX STI EJ207 276 bhp @ 6500 rpm 260 lb-ft @ 4000 rpm 8000
GF8 Wagon WRX EJ205 237 bhp @ 6500 rpm 228 lb-ft @ 4000 rpm 7200
GF8 Wagon WRX STI EJ207 276 bhp @ 6500 rpm 260 lb-ft @ 4000 rpm 8000
BE5 Sedan GT EJ206 256 bhp @ 6000 rpm 235 lb-ft @ 5000 rpm 7000
BE5 Sedan RSK EJ208 276 bhp @ 6400 rpm 253 lb-ft @ 5000 rpm 7500
BH5 Wagon GT EJ206 256 bhp @ 6000 rpm 235 lb-ft @ 5000 rpm 7000
BH5 Wagon RSK EJ208 276 bhp @ 6400 rpm 253 lb-ft @ 5000 rpm 7500
SF5 SUV S, S/tb, T/tb, STI EJ205 237 bhp @ 6500 rpm 228 lb-ft @ 4000 rpm 7200

*OEM published rating

# Turbo Specifications

# Single Turbo

Engine Turbo Peak Boost (bar) Max Airflow (g/s)
EJ205 TD04HL-(15T?) 0.74 215
EJ207 Rev.F VF28 1.08 (WRX 1.0) 255
EJ207 Rev.G VF29 1.08 (WRX 1.0) 255

# Twin Turbo

Engine Turbo (Primary / Secondary) Peak Boost (Primary / Secondary, bar) Max Airflow (g/s)
EJ206 Rev.A,B VF25 / VF27 0.70 / 0.85 245
EJ206 Rev.C VF31 / VF32 0.94 / 0.94 245
EJ208 Rev.A,B VF26 / VF27 0.78 / 0.98 245
EJ208 Rev.C VF31 / VF32 0.94 / 1.00 245
Last Updated: 11/13/2019, 9:54:00 PM