ECU in a modern vehicle makes it possible to control many aspects of
the engine's operation, such as spark timing and fuel injection. The
ECU may also control electronic throttle control (drive-by-wire), valve
timing, boost control (in turbocharged engines), ABS, the automatic
transmission, speed governor (if equipped), and the electronic
stability control system.
Performance increases are achieved by
adjusting the ignition timing advance. Higher timing may result in
higher performance. However, to cope with advanced timing, one must run
high-octane petrol to avoid pre-ignition detonation or pinging.
Manufacturers design for a specific timing and this may limit
In addition, changing fuel maps to
coincide with the stoichiometric ratio for fuel combustion may also
achieve performance increases. Most manufacturers tune for optimum
emissions and fuel economy purposes which often limit performance.
with a turbo fitted can have the requested and allowable boost levels
raised, these applications usually have the most effect if the turbo
fitted is a low pressure turbo which leaves the most room for
Another reason to change the ECU map is if there
are engine, intake, or exhaust modifications to the car. These
"bolt-on" modifications alter the way that the engine flows, often
causing the air to fuel ratio to change. Without re-mapping the fuel
tables, some of the performance gains from the modifications may not be
A poorly tuned ECU can result in decreased performance, driveability, and may even cause engine damage.
most common way to 'upgrade' the ECU is using an OBD Flash tool. These
devices plug into the diagnostic port although in some cases the
reprogramming is done directly on the circuit board. Maps are supplied
by expert tuners like Revo and Oscarli.
An alternative to
modifying the on-board chip is adding an external device, often known
as a tuning box e.g. Steinbauer. The abilities of the external devices
generally reflect on-board chip modifications, with the advantage that
they can be easily removed to restore the vehicle to standard. Adding
an external tuning box is generally only possible on modern engines
with external management ports.
(With thanks to Wikipedia for some of the content)