What is an ECU and why do I need one?

 

What is an ECU?

An ECU, or Engine Control Unit, is a small computer which controls an engine. Usually "ECU" refers to an ECU on a electronically fuel injected (EFI) petrol engine. ECUs also go by several other names, such as EMS (Engine Management System), ECM (Engine Control Module), or even "chip" (derived from the practice of replacing the ROM chip in the factory ECU to retune it).

The ECU usually controls the fuel injection amount and the ignition timing of the engine, along with several other functions. Because the ECU controls the fuel injection amount, it must be set up correctly, otherwise poor fuel economy, poor power and excess pollution may result.

Most people don't. Every EFI car comes with one from the factory, and that ECU is tuned for that engine. Manufacturers spend lots of time making sure the ECU is tuned correctly for that engine, and that drivability, fuel economy, power and emissions targets are all met. Unless you've got a good reason, there's usually not any benefit to be gained by replacing the factory ECU.

On the other hand, if you have modified your engine (eg larger exhaust, ported head or increased boost), it's possible that your factory ECU will not be correctly tuned for the engine. This is because the modifications to the engine make it behave differently (otherwise, people wouldn't do them), and many factory ECUs will not adapt to the different behaviour of the engine.

How does an Aftermarket/Programmable ECU differ from the factory ECU?

To enable people to set up their ECU for their modified engine, aftermarket ECUs are "programmable". This means that the installer can connect some form of controller (often a laptop PC) to the ECU, to enable its settings to be configured. A factory ECU does not (usually) allow this behaviour. If it did, one would just reprogram the factory ECU (this practice is sometimes done by replacing a ROM chip in the factory ECU, although this is not as flexible as a replacement ECU).

What's so special about the Adaptronic?

Because the amount of fuel required by engines differs under different conditions (eg throttle position) and between different engines, the ECU must be tuned for the particular engine. This process must be repeated when other modifications to the engine are made. This can often take a lot of time to perform, even for an experienced tuner, because the tuner has to manually adjust the fuel mixture on the ECU, and retest the engine, for hundreds of different conditions. Time on a dynamometer can be quite expensive, leading to a very expensive engine modification.

There is another method, which is where the ECU automatically adjusts the mixture strength to the user's specification. This greatly speeds up the tuning procedure. This technology has been employed by MoTec (Quick Lambda) and Autronic (Autotune), however their use appears limited to tuning on a dynamometer.

The Adaptronic has been designed from the ground up to run continuously in adaptive mode. This means that after performing changes such as a new exhaust system, the user merely needs to continue to drive the car on the street, and the ECU will automatically adapt to the changes made.

This makes life easier for vehicle modifiers and the end user, while encouraging responsible car tuning, leading to less pollution from modified cars generally.