TERMS AND DEFINITIONS OF FUEL INJECTION MANAGEMENT SYSTEMS

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.

• 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.

MULTI-POINT FUEL INJECTION (MPFI) - In the multi point fuel injection system an injector is located in the intake manifold passage. The fuel is supplied to the injectors via a fuel rail in the case of top fed fuel injectors and via a fuel gallery in the intake manifold in the case of bottom fed fuel injectors. MPFI systems provide better performance and fuel economy as compared to TBI. Most of the MPFI systems use one injector per cylinder but in certain applications up to two injectors per cylinder are used to supply the required fuel for the engine.

CENTRAL MULTI-PORT FUEL INJECTION (CMFI) - This is a variation of MPFI system but in this case the injectors (usually one per cylinder) are located in a plastic molded pod and the fuel is distributed to the intake ports via a polymeric hose. To avoid fuel distribution variations a fuel pressure activated poppet valve is installed at the end of the hose. The injectors are activated via the ECU in a similar fashion as in the MPFI fuel systems.

TUNED PORT INJECTION (TPI) - A TPI is a fuel/air management system that has a tuned induction system to optimize air flow to each cylinder. This system was developed to obtain the broadest possible torque curve. A single throttle body and one injector per cylinder are used in this configuration. The intake manifold incorporates long runners whose length is tuned to the desired torque curve. For low and mid range torque longer runners are utilized in this application.

DIRECT FUEL INJECTION (DFI) - In a direct fuel injection system one injector is located in the cylinder head for each cylinder. The high-pressure fuel (single fluid) or low-pressure air/fuel mixture (dual fluid) is metered directly into the combustion chamber when the electromagnetic valve is activated by the ECU. This fuel injection system offers the latest in engine management systems and offers the best in engine performance, low exhaust emissions and fuel economy.