What Exactly is ECU Remapping ?

Modern cars are equipped with electronic engine management systems, whether it be a carburetor like central injection, the much more effective multiport injection or a direct injection with common rail technology with electronic charge pressure control.
The most important development in engine efficiency was the ECU (engine control unit). This device consists of one or more small microcomputers which are responsible for the regulation of the engine settings. The microcomputers run a program which is stored in a Memory (Eprom/Flash) device. The ECU is responsible for the whole engine management & controls, verifies, navigates & adjusts all of the important functions of the car and engine. This all happens under consideration of the current load condition of the engine in conjunction of the RPM & environment variables such as outside temperature, air density & engine temperature. This is possible with the information from many sensors which measure fuel pressure, temperature, rpm, vehicle speed, & air mass with very high precision. Then the ECU reads the stored values out of the predefined maps for the injection, ignition, charge pressure & lambda. This way, the best possible ignition timing & the optimal amount of fuel in combination with the correct charge pressure is calculated out of the maps in conjunction with the sensor values.
All of this data is optimized at the chip-tuning (remapping) process. This means that the maps for injection (for petrol cars also ignition) & charge pressure, are measured in conjunction to each other in the whole rpm band, recalculating & optimised in relation to load & RPM. This happens in a way that the maximum possible power & torque is gained, while the tolerances for the long life time of the engine is still kept, & the maximum possible fuel economy is reached. Keeping this in mind, a noticeable power increase & also a stronger torque of the engine is gained. Power & torque improvement of 20-40% with Turbo charged engines, & 10-20% for normal aspirated engines are achievable, giving great improvements for acceleration, agility & a small gain on top speed.
The engine becomes much more agile & stronger, while the lifetime, & the every day use of the engine is at normal use & regular service intervals the same as for the stock settings.
The main purpose at normal gasoline cars is the regulation of the requested & maximal possible amount of injection. Since the air to fuel ratio needs to be very precise to let the catalytic converter work flawlessly, the injected amount of fuel depends on the amount of air that is available. In addition the optimal ignition point needs to be determined, when the compressed air/fuel mixture is fired. If the ignition point is to late, the consumption will raise, if it is to early the car will start pinking (knocking). In addition the ECU has many other purposes, which will not be changed. With modern diesel engines the amount of injection is calculated from the amount of air volume, air pressure, outside temperature, rpm & load. This is needed to keep the emission restrictions within limits. With turbo diesel engines, beside this the charge pressure & charge volume of the Turbochargers needs to be defined load & rpm dependent. All of this information is stored in the Eprom flash of a modern ECU. From these values (maps) the ECU calculates the special RPM & load condition possible for the needed amount of fuel injection.
After 1996 almost all cars were fitted with an ECU & from the year 2.0 all petrol engined cars have a standard OBD (OnBoard Diagnostics) port for diagnostics & ECU control, for diesel engined cars the standard was introduced in 2004. Remapping involves copying the program from the ECU & making fine adjustments to increase performance, improve fuel economy or both.