Filed Under (Tips and Review) by admin on 19-11-2010

Throttle Body Assembly (TBA) — The throttle body assembly (also called air valve), controls the airflow to the engine through one, two or four butterfly valves and provides valve position feedback via the throttle position sensor. Rotating the throttle lever to open or close the passage into the intake manifold controls the airflow to the engine. The accelerator pedal controls the throttle lever position. Other functions of the throttle body are idle bypass air control via the idle air control valve, coolant heat for avoiding icing conditions, vacuum signals for the ancillaries and the sensors. FUEL INJECTOR — There are basically three approaches in delivering the fuel to the engine: • Above the throttle plate as in throttle body injection • In the intake port toward the intake valves as in multi-port injection or central multi-port injection. • Directly into the combustion chamber as in gasoline direct injection systems (GDI). The fuel injector is continuously supplied with pressurized fuel from the electric fuel pump. The pressure across the metering orifice of the injector is maintained constant by the fuel pressure regulator. The fuel injector is an electromagnetic valve that when driven by the ECU delivers a metered quantity of fuel into the intake manifold (or combustion chamber in the GDI system). The ECU controls the fuel flow by pulse width modulation. The time the injector is driven into an open condition is determined by the following sensor inputs: • Engine RPM • Throttle position (TPS) • Manifold absolute pressure or mass air flow • Engine coolant temperature • Oxygen sensor feedback voltage • Intake air charge temperature • Battery voltage CENTRAL POINT INJECTION SYSTEM (CPI) — Electronic fuel Injection system consisting on a single fuel injector mounted in the throttle body. DIGITAL FUEL INJECTION (DEFI OR DFI) — Electronic fuel injection system controlled by digital microprocessors as opposed to earlier systems that were of analog design. The analog input signals to the microprocessor are converted from analog to digital before being processed.

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