How a car Fuel Injection System Works
A fuel injection system is used to inject fuel with an injector, under pressure into an internal combustion engine.
A fuel injection system is more efficient than its predecessor thecarburetor and can better operate at extreme temperatures while becoming more dependable at start up. A fuel injection system reacts better to situations such as high altitudes, extreme temperatures and variable fuel quality.
The fuel injection system is an integral part of a modern cars engine management system. Afuel pump, usually located inside of the fuel tank, supplies pressurized fuel for the system. The fuel pressure is controlled by apressure regulator according to demand on the vehicle. Ultimately the amount of fuel that goes into the engine is determined by the engine management system according to information (feedback data) gathered by the sensors.
Typical Fuel Injection System
A fuel injection system is more efficient than its predecessor the carburetor and can better operate at extreme temperatures while becoming more dependable at start up. A fuel injection system reacts better to situations such as high altitudes, extreme temperatures and variable fuel quality.
Fuel metering is determined by a combination of the engine air charge, vacuum and speed. Some vehicle utilize amass airflow sensor to determine engine air intake, other systems use a MAP sensor (manifold absolute pressure). Both utilize oxygen sensors to monitor emissions in the exhaust to help control mixture.
Mass Air Flow Sensor
A throttle position sensor located on the throttle body, is used to measure the load on the engine according to engine speed/vehicle speed/throttle position and other information gathered by the computer.
The fuel injector nozzle directs liquid fuel into the engine intake air stream. The fuel system is controlled by a computer called a Powertrain Control Module (PCM). The PCM controls the fuel injection system by gathering and processing information from numerous sensors mounted into the system. There are basic sensors used to determine the amount of fuel used, such as:coolant temperature sensor, oxygen sensor, air intake temperature,knock sensor,crankshaft angle sensor, camshaft angle sensor and a mass air flow sensor. A fuel injector is normally closed and only opens when the injector driver inside the PCM commands it to. The duration of this opening is called the pulse width.
Common Problems and Fixes
Since most injection systems are computer based a simple hook up to adiagnostic scanner will generally let you know what the problem is. Simply replace the shorted sensor or repair thevacuum leak. Then clear the trouble codes and recheck system. One hazard while servicing a fuel injection system is the pressure involved. Use caution and slowly loosen the fuel line to bleed off pressure.