All vehicles with the 4.6L and 5.0L engines are equipped with a Sequential Electronic Fuel Injection (SEFI) system. In this system, fuel is metered into each intake port in sequence with the engine firing order, according to engine demand, through fuel injectors mounted on a tuned intake manifold.
The SEFI system consists of two subsystems, the fuel delivery system and the electronic control system. The fuel delivery system supplies fuel to the fuel injectors at a specified pressure. The electronic control system regulates the flow of fuel from the injectors into the engine.
The fuel delivery system consists of an electric fuel pump, fuel filters, fuel supply manifold (fuel rail), fuel pressure regulator and fuel injectors. The electric fuel pump, mounted in the fuel tank, draws fuel through a filter screen attached to the fuel pump/sending unit assembly. Fuel is pumped through a frame mounted fuel filter, to the engine compartment, and into the fuel supply manifold. The fuel supply manifold supplies fuel directly to the injectors. A constant fuel pressure to the injectors is maintained by the fuel pressure regulator. The fuel pressure regulator is mounted on the fuel supply manifold, downstream from the fuel injectors. The excess fuel supplied by the fuel pump but not required by the engine, passes through the regulator and returns to the fuel tank through the fuel return line. The fuel injectors spray a metered quantity of fuel into the intake air stream when they are energized. The quantity of fuel is determined by the electronic control system.
Air entering the engine is monitored by speed, pressure and temperature sensors. The outputs of these sensors are processed by the Powertrain Control Module (PCM). The PCM computes the required fuel flow rate and determines the needed injector pulse width (injector "on" time) and sends a signal to the injector to meter the exact quantity of fuel. Each fuel injector is energized once every other crankshaft revolution, in sequence with the ignition firing order.
For description and testing of electronic control system components, see Emission Controls .
See Figure 1
FUEL SYSTEM SERVICE PRECAUTIONS
Safety is the most important factor when performing not only fuel system maintenance, but any type of maintenance. Failure to conduct maintenance and repairs in a safe manner may result in serious personal injury or death. Work on a vehicle's fuel system components can be accomplished safely and effectively by adhering to the following rules and guidelines.