Contents: Air intake system ↓ Throttle body for 1999-2003 models. ↓ Throttle body on 2004 and later…↓ Electronic control system ↓ Fuel supply system ↓
The SFI system consists of a fuel tank, an electric fuel pump submerged in the tank, and a fuel pressure regulator (integral part of the pump), eFI main relay, disconnect relay (fuel pump relay), the fuel rail and fuel injectors. The air intake system includes the air cleaner, air intake duct, and throttle body. The throttle body on all 1999-2003 models is a conventional cable-operated unit. The throttle body on 2004 and later models is an electronic unit controlled by the PCM. On these models, the PCM monitors the angle of the accelerator pedal via a sensor in the accelerator pedal and commands the solenoid valve in the throttle body to change the angle of the throttle plate in the throttle body accordingly. Since all of these components are part of the engine management system, the SFI system and the various emission control systems used on these vehicles work together. For emission control system information, refer to chapter 6. The SFJ system is fairly easy to understand if you break it down into three subsystems: the air intake system, the electronic control system, and the fuel delivery system.
Air intake system
The air intake system consists of an air filter, an intake manifold, resonators, a throttle body, and an intake manifold. Resonators are specially shaped chambers attached to the intake manifold. They act as accumulators or receivers that help "calm" the air flow through the intake manifold. Replacement procedures for all of these components are covered in this chapter (except for intake manifolds, which are covered in Chapter 2A or 2B).
Throttle body for 1999-2003 models.
The throttle body on 2001-2003 models with a four-cylinder engine has a conventional single-channel design. The lower part of the throttle body is heated by engine coolant, which helps prevent icing of the body in cold weather. A throttle position sensor (TP) is installed on the valve axis, which allows monitoring changes in the throttle opening angle. An engine idle speed control valve (ISC) is connected to the underside of the throttle body. For information about the TP sensor and ISC valve, refer to chapter 6.
The V6-powered throttle body on the 1999-2003 medals is a two-channel design that includes a three-stage variable geometry intake system (ACIS). Similar to the single-channel throttle body used on models with a four-cylinder engine, the dual-channel throttle body used on models with a V6 engine is also equipped with a throttle position sensor (TP) and an engine speed control valve in idle mode (ISC). For more information about the ACIS system, the TP sensor, and the ISC valve, refer to chapter 6.
When the engine is idling, the air-fuel ratio is controlled by the idle speed control (ISC) system. The ISC system consists of the engine coolant temperature (ECT) sensor, intake air temperature (IAT) sensor, throttle position (TP) sensor, mass air flow (MAF) sensor, various other sensors, the powertrain control module (PCM), and the ISC valve. The ISC valve is activated by the PCM under certain conditions, such as cold cranking, power steering load at low vehicle speeds, or when the air conditioner is on. The ISC valve regulates the amount of air that bypasses the throttle plate and enters the intake manifold. For more information on the ISC valve and the ISC system, refer to chapter 6.
Throttle body on 2004 and later models
The throttle body on the 2004 and later four-cylinder and V6 models is equipped with the ETCS-i electronic accelerator control system. The single-channel throttle body on these models is an electronic unit, meaning it doesn't use an accelerator cable to open and close the throttle. Instead, a DC electric motor is installed, which opens and closes the throttle valve inside the housing in response to a command from the power unit control module (PSM). The PCM module monitors the position or angle of the accelerator pedal using the Accelerator pedal Position sensor (APP), and then commands the DC motor inside the throttle body to open or close the throttle accordingly. Such a throttle body is equipped with a throttle position sensor (TP), but, unlike earlier units, the sensor is an integral part of the throttle body and cannot be removed. These units do not have an engine idle speed control valve (ISC). The idling engine speed control function is controlled by the PCM. For more information about the ETCS-I system, APP and PCM sensors, see chapter 6.
Electronic control system
The information sensors, powertrain control module (PCM), output actuators and various emission control systems used on these vehicles are described in chapter 6.
Fuel supply system
The fuel supply system includes a fuel pump, fuel pressure regulator, fuel filter, fuel lines, pressure pulsation damper, fuel rail and fuel injectors. The fuel pump, built into the tank, is an electric linear pump. Fuel is drawn into the pump through the inlet screen filter, passes through the pressure regulator, through the fuel filter and is supplied to the injectors. The fuel pressure regulator maintains constant pressure in the injectors.
The injectors are electromagnetically driven, constant stroke, needle type. They consist of an electromagnet, plunger, needle valve and housing. When current is applied to the electromagnet, the needle valve comes out of its seat, and a jet of fuel under pressure comes out of the injector housing through the atomizer. The cyclic supply depends on the pulse duration, that is, the period of time during which the needle valve is open, during which time, in turn, is determined by the period of time during which current is supplied to the electromagnet. Since the injection advance of the injector determines the opening and closing intervals, which, in turn, determine the air-fuel ratio of the injected mixture, the injection advance of the injector must be very accurate.
The EFI main relay, located in the fuse/relay box in the engine compartment, supplies power to the fuel pump relay (opening relay) via the ignition switch. The PCM controls the ground signal suppressed to the fuel pump in response to the crank signal and the camshaft position signals at crank.