Electronic fuel injection of internal combustion engines is an accurate means of preparing the proper air-to-fuel mixture for the individual cylinders under all operating conditions. The precise amount of fuel required by the engine for any given cycle depends directly upon the amount of air ingested during each stroke.
Fuel delivery is accurately regulated via a number of sensors located strategically around the engine. These sensors convert physically measurable quantities, such as engine speed and manifold absolute pressure, into proportional electrical signals which are processed by an electronic control unit (ECU). The ECU, in turn, is programmed to determine nearly instantaneously the amount of fuel necessary to ensure the highest torque, best fuel economy, and lowest exhaust emissions under the prevailing conditions represented by the input sensor signals. Fuel delivery to each cylinder is controlled by a precision electromagnetic valve (injector) whose on-time is determined by the width of the command pulse generated by the ECU.
The information required to calibrate the ECU for a given engine is obtained from characterization studies; the data thus acquired are reduced to a matrix which can be described as a three-dimensional control surface. The basic calibration can be modified to enrich the fuel mixture for cold start, warmup, hot engine restart, and transients by means of the temperature and throttle angle sensors.