Fuel Injection System

The Sequential Multiport Fuel Injection (SFI) system is classified as a multi-point, pulse time, mass air flow, 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 in conjunction 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 and computes the timing and the duration that the electrically operated fuel injectors are energized.

The basic fuel requirement of the engine is determined from the data supplied to the PCM by the Mass Air Flow (MAF) sensor, which measures the amount of air being drawn into the engine. Other sensors and switches are used to measure:

- Intake air temperature
- Coolant temperature
- Engine speed
- Exhaust oxygen content

The various sensors and switches detect any changes in the operating conditions and send signals to the PCM. This permits the PCM to control the opening duration (pulse width) of the fuel injectors and maintain optimum exhaust emission control and engine performance for all operating conditions.

FUEL INJECTION TIMING
During engine cranking with a PCM malfunction or where no camshaft sensor signal is detected, fuel is supplied by providing two injections for every crankshaft rotation (four injections per cycle) to all cylinders.

An electrical signal from the PCM activates the injector solenoid, causing the plunger to move inward off the seat, allowing fuel to flow.

Between idle and 6,500 rpm the fuel is injected to each cylinder independently by giving one injection per two crankshaft rotations to all cylinders.

When engine speed exceeds 6,500 rpm, fuel is cut to prevent engine over-speeding and possible engine damage.

Injection Timing:

Major components of the fuel system include:
- Fuel pump
- Fuel filter
- Fuel injection supply manifold
- Fuel pressure regulator
- Fuel injector
- Fuel pump relay

The fuel pump supplies filtered, pressurized fuel to each fuel injector through the fuel injection supply manifold. The fuel pump is mounted in the fuel tank to minimize operating noise. The fuel pressure is regulated by a fuel pressure regulator, which is located at the return line side of the fuel injection supply manifold. The fuel injectors are directly supplied with battery voltage through the PCM.

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