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

Upgrades that can be done with Lambda Tuning:

  • Live Tuning
  • Speed Density fueling mode (Single turbo firmware only for now)
  • 2-step launch rev limiter
  • Boost Control improvements
    • Tunable wastegate solenoid output frequency
    • Boost target map interpolation
    • Wastegate duty map interpolation
    • Proportional wastegate duty control
  • Wideband Lambda 5V input O2 sensor upgrade
  • Faster knock sensor logging speed

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.

Tips

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.

Warning

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.

The narrowband O2 can also be upgraded to a Wideband Lambda sensor with a 5V output.

Upgrades

Fuel Pump

OEM 480cc 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.

Tips

After upgrading, check the fuel pressure as some pumps can exceed the fuel pressure regulators flow capacity. Static fuel pressure should be 300 kpa / 43.5 psi.

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. Wastegate solenoid output frequency can be increased to an appropriate setting for the solenoid installed.

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.

Warning

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).

Warning

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

ModelRevisionProduction DatesChanges
ImprezaGC8F/GF8F09/1998 — 09/1999Initial release
ImprezaGC8G/GF8G09/1999 — 09/2000Turbo changed to VF29
LegacyBE5A/BH5A06/1998 — 04/1999Initial release
LegacyBE5B/BH5B05/1999 — 04/2000No change
LegacyBE5C/BH5C05/2000 — 04/2001Upgraded ignition coils, VF31/VF32 turbos
ForesterSF5B09/1998 — 12/1999Initial release
ForesterSF5C01/2000 — 12/2000No change
ForesterSF5D01/2001 — 01/2002No change

Engine Specifications

Chassis CodeBodyTrimEnginePower*Torque*Rev Limit
GC8SedanWRXEJ207276 bhp @ 6500 rpm250 lb-ft @ 4000 rpm7600
GC8Sedan, CoupeWRX STIEJ207276 bhp @ 6500 rpm260 lb-ft @ 4000 rpm8000
GF8WagonWRXEJ205237 bhp @ 6500 rpm228 lb-ft @ 4000 rpm7200
GF8WagonWRX STIEJ207276 bhp @ 6500 rpm260 lb-ft @ 4000 rpm8000
BE5SedanGTEJ206256 bhp @ 6000 rpm235 lb-ft @ 5000 rpm7000
BE5SedanRSKEJ208276 bhp @ 6400 rpm253 lb-ft @ 5000 rpm7500
BH5WagonGTEJ206256 bhp @ 6000 rpm235 lb-ft @ 5000 rpm7000
BH5WagonRSKEJ208276 bhp @ 6400 rpm253 lb-ft @ 5000 rpm7500
SF5SUVS, S/tb, T/tb, STIEJ205237 bhp @ 6500 rpm228 lb-ft @ 4000 rpm7200

*OEM published rating

Turbo Specifications

Single Turbo

EngineTurboPeak Boost (bar)Max Airflow (g/s)
EJ205 EU SF5TF035HM-14T0.54190
EJ205 EU GC8TD04HL-13T/60.94215
EJ205 JDMTD04HL-13T/60.74215
EJ207 WRXVF28 or VF291.00255
EJ207 STIVF28 or VF291.08255

Twin Turbo

EngineTurbo (Primary / Secondary)Peak Boost (Primary / Secondary, bar)Max Airflow (g/s)
EJ206 Rev.A,BVF25 / VF270.70 / 0.85245
EJ206 Rev.CVF31 / VF320.94 / 0.94245
EJ208 Rev.A,BVF26 / VF270.78 / 0.98245
EJ208 Rev.CVF31 / VF320.94 / 1.00245
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