Fuel Charging System

The Sequential Multiport Fuel Injection (SFI) system is a multi-point, pulse fuel injection system. This system supplies the engine with the air/fuel mixture necessary for combustion. An air induction system and fuel injection system work with an electronic engine control system which consists of various sensors, switches, and a Powertrain Control Module (PCM). All sensors and switches are connected to the PCM, which interprets the data it receives and computes when and for what period of time the electrically-operated fuel injectors are energized. The PCM increases, decreases, or cuts off fuel delivery to the fuel injectors based on engine demands and driving conditions.

The fuel charging system consists of:
- Fuel pump
- Fuel filter
- Fuel injection supply manifold
- Fuel pressure regulator
- Fuel injectors
- Fuel pump relay
- Fuel tank
- Inertia fuel shutoff switch (IFS switch)

When the ignition is ON, the Powertrain Control Module Relay (PCM Relay) turns ON, providing power to the PCM, fuel pump relay, and the fuel injectors. Power to the fuel pump is supplied through the fuel pump relay. The IFS switch is a safety device used to shut off the fuel pump in the event of a collision. It is connected between the fuel pump and the fuel pump relay. If the IFS switch is "tripped", it must be reset by depressing the button on top of the switch. During engine cranking, the fuel pump circuit is completed by the PCM closing the contacts in the fuel pump relay, energizing the fuel pump.

The basic fuel requirement of the engine is determined from the data supplied to the PCM by the Mass Air Flow Sensor (MAF Sensor). The MAF sensor measures the amount of air being drawn into the engine. Other sensors and switches are used to measure:
- Air temperature
- Atmospheric pressure
- Coolant temperature
- Engine crankshaft and camshaft speeds
- Exhaust oxygen content

An electric fuel pump is mounted in the fuel tank and supplies filtered, pressurized fuel to each fuel injector through the fuel injection supply manifold. Fuel is filtered by an in-line fuel filter. The fuel pressure is regulated by a fuel pressure regulator which is located at the return line side of the fuel injection supply manifold.

Typical Injection Timing:

Fuel is metered and injected into the intake ports according to the fuel injector signals received from the PCM. When these injection signals are applied to the coil of the fuel injector, the needle valve is pulled off its seat. Fuel is then injected around the back face of the intake valve. The amount of fuel supplied to the engine depends on the length of time that the fuel injectors stay open.

Between idle and 6,500 rpm, fuel is injected to each cylinder independently, providing one injection per two crankshaft rotations (one injection per cycle) to all cylinders. When engine speed reaches 6,500 rpm, fuel injection is shut off in order to prevent the engine from over-speeding.