Getting an ECU upgrade for your Subaru WRX or STi is as easy today as taking your car to your local Subaru tuner but the importance of this single component often gets overlooked.  An ECU upgrade will ensure that all parts of your Subaru WRX are working in harmony together and is one of the best know ways to get increased power from your car.

The Subaru WRX ECU (Engine Control Unit) is an extremely sophisticated and powerful piece of equipment included pretty much from Version VII Subaru WRX and onwards. The Subaru WRX ECU chip operates like any other computer, taking information from a wide variety of sensors, processing the collected data, and based on this, generates a number of output functions.

It is these output functions that determine actual engine operating parameters such as the amount of fuel injected, ignition advance and turbo boost pressure to name but a few.

These are complex calculations, with the input/process/output routine repeating on a continuous basis over and over again. In addition the ECU continually error checks the validity of inputted data, and its own internal calculations compared against the actual operation and performance of your Subaru in order to keep the engine operating safely.

Memory chips that can be erased and reprogrammed on the fly countless times have been used in wide variety of electronic consumer goods for years. The attraction for vehicle manufactures is obvious, an ECU chip can be standardised for use across a wide range of cars with only a calibration data change required. More importantly, it is exceptionally easy to perform an ECU upgrade or apply a “patch” throughout the life of the car in response to possible engine management or emissions issues.  Talk to your local performance workshop to find out if you need an ECU upgrade for your Subaru WRX ECU.

In typical form, the aftermarket has wasted no time latching onto this feature, with companies such as EcuTeK, Cobb and Techtom exploiting this new found functionality, marketing engine calibration software of varying sophistication. So much so, craggy grease-stained blokey type mechanics are no longer the real horsepower heroes, as this title has shifted across to pointyheaded software programmers. It is revenge of the nerds, real-time and in your car! But they have managed to turn the Subaru WRX ECU upgrade into a very simple exercise.

The evolutionary process of the WRX engine management systems can be described in four broad steps, with the advent of flash re-tuning of the OE ECU being the defining factor. Flash tuning is something of a revolution in the aftermarket performance industry, and is discussed in more detail in the Subaru Performance Handbook.
OE Subaru ECU’s are divided into the following:

  • Pre-flash – The Version I-IV ECU  was very much the dark ages when it came of performance tuning. Early models could be modified with the addition of a plug-in ECU chip, but with limited results.
  • Flash 99-00 – first Subaru ECU upgrade to allow commercially viable flash re-tuning, in addition to a sophisticated ECU generated data stream, accessible via the OBDII data port. Fuel and ignition timing are calculated by referencing grams per second of air mass against RPM.
  • Flash 02 – current generation ECU upgrade, as fitted to Subaru WRX models and the Australian spec Subaru STi. Supports active variable camshaft system (AVCS) but not drive by wire (DBW). Uses a much more sophisticated fuel and ignition calculation, expressed in grams per cylinder charge, determined by a combination of mass air flow, manifold pressure and throttle position.
  • Flash 04 – the very latest ECU upgrade used by Subaru, continuing on with the control architecture of Flash 02, with the addition of key features such as DBW throttle control and CAN bus communication protocols. Used by range topping Subaru XT Forester and USDM Subaru STi variants as well as the MY06 onwards Impreza WRX and STi. Liberty/Legacy GT models feature double AVCS (both intake and exhaust cam control).

In the past, even relatively simple performance parts exceeded the capacity of the OE ECU, to the point of becoming somewhat of a liability in terms of power and reliability. The advent of EcuTeK has changed this, as now the OE ECU can be sent back to school for some elocution lessons. Seasoned engine tuners that previously have had no experience with flash ECU tuning, can often be heard to exclaim “I see the light” over and over when using EcuTeK for the first time. In terms of sophistication and functionality, none of the aftermarket engine management products currently available come close to matching that of the OE ECU.

Reprogramming the OE ECU is by and far the best method of undertaking an ECU upgrade and ensuring you correctly compensating for the effects of mechanical tuning on engine operation. It is simply the quickest, easiest and safest way to come up with a tune to suit most modifications that are ever likely to be performed. Advantages of reprogramming the OE ECU include;

  • No need for risky electronic boost clamps, bleed valves, add-on interceptors or boost controllers that otherwise dilute the functional simplicity of the OE management system.
  • No modifications to wiring or sensors are required, eliminating the potential for system failures caused by badly cut or spliced wiring.
  • Repair and diagnosis of a re-flashed ECU remains exactly the same as before. System fault tracing and diagnosis is unchanged simplifying maintenance operations, especially in remote areas away from “specialist” tuners.
  • All the inbuilt refinements of the OE system are retained during the ECU upgrade, such as civilised hot and cold starting, throttle response and idle quality.
  • Tuning the engine does not have to start from scratch, as the process of optimising performance starts with a set of fuel and ignition maps that are very good to start with. Additionally, only areas of the OE mapping that need to be changed are adjusted, instead of having to start from a clean sheet of paper.
  • All adaptive functions of the Subaru WRX ECU are retained during the ECU upgrade and can be improved in their operation to harmonise completely with mechanical tuning modifications. Closed loop to open loop fuel control transition points are adjusted to improve engine durability and driveability. Active ignition timing control parameters are modified to increase both engine power and driveability. While reliability is maintained by adjusting the system to react more appropriately in response to the increased intensity at which a modified engine will detonate at.
  • Sophisticated safety features built into the OE ECU are maintained, such as sensor error checking, boost and RPM limiting. The latest ECU upgrade also has the ability to dynamically intervene in the event of detectable problems, and as it is still in full control of the boost control system, it can command boost reductions in an attempt to protect the engine from damage.

The adjustable parameters via EcuTeK include:

  • Base ignition mapping, active ignition parameters and compensations for temperature and pressures.
  • Base fuel mapping, closed loop operational parameters and compensations for temperature and pressures.
  • Desired boost pressure, overboost safety cut limit, turbo dynamics (to suit different turbos and exhaust characteristics), minimum and maximum wastegate duty cycles and boost pressure based speed limiting.
  • Engine idle speed.
  • Fuel injector scaling.
  • Air mass sensor input scaling.
  • And a whole lot more!

What does this mean? In the hands of a skilled engine tuner, substantial improvements to power and driveability are easily within reach without sacrificing any of good features that set the OE ECU apart from anything else available in the aftermarket. Power gains of up to 20kW can be made on otherwise un-modified late model WRX with a simple ECU reflash. When combined with parts such as an exhaust and intake, power increases of 40kW and more can be made over standard. In practice there seems to be really no effective power level at which the OE ECU cannot achieve, although it takes a very skilled operator and a lot more than just a passing familiarity with EcuTeK to extract really big power outputs.

Understanding how the Subaru WRX ECU works and how much better your WRX can run after an ECU upgrade will make it far easier to get top performance from all parts of your car.

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