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SEQUENTIAL ELECTRONIC FUEL INJECTION (SEFI)
General Information
The Sequential Electronic Fuel Injection (SEFI) system is used on all Super High
Output (SHO) vehicles, as well as on 1993 and later 3.0L and 3.8L engines. It is
classified as a multi-point, pulse time, speed density control fuel injection system.
The fuel is metered into the intake manifold port, in sequence, in accordance with
the engine demand through the injectors mounted on a tuned intake manifold.
The Electronic Engine Control (EEC-IV) computer outputs a command to the fuel
injectors to meter the appropriate quantity of fuel. The remainder of the fuel
system is basically the same as the EFI system installed on some earlier model
3.0L and 3.8L engines.
The SEFI fuel subsystem includes a high pressure (30-45 psi/209-310 kPa) tank-
mounted electric fuel pump, fuel charging manifold, pressure regulator, fuel filter,
and both solid and flexible fuel lines.
The fuel pressure regulator maintains a constant pressure drop across the injector
nozzles. The regulator is referenced to intake manifold vacuum and is connected
parallel to the fuel injectors and positioned on the far end of the fuel rail. Any
excess fuel supplied by the pump passes through the regulator and is returned to
the fuel tank via a return line.
The fuel pressure regulator is a diaphragm operated relief valve in which one side
of the diaphragm senses fuel pressure and the other side senses manifold
vacuum. Normal fuel pressure is established by a spring preload applied to the
diaphragm. Control of the fuel system is maintained through the EEC-IV power
relay and the EEC-IV control unit, although electrical power is routed through the
fuel pump relay and an inertia switch. The fuel pump relay is normally located on
a bracket somewhere above the Electronic Control Assembly (ECA) and the inertia
switch is located in the storage compartment. Tank-mounted pumps can be either
high or low pressure, depending on the model.
The fuel injectors used with the SEFI system are an electromechanical (solenoid)
type designed to meter and atomize fuel delivered to the intake ports of the
engine. The injectors are mounted in the lower intake manifold and positioned so
that their spray nozzles direct the fuel charge in front of the intake valves. The
injector body consists of a solenoid actuated pintle and needle valve assembly.
The control unit sends an electrical impulse that activates the solenoid, causing
the pintle to move inward off the seat, allowing the fuel to flow. The amount of
fuel delivered is controlled by the length of time the injector is energized (pulse
width), since the fuel flow orifice is fixed and the fuel pressure drop across the
injector tip is constant. Correct atomization is achieved by contouring the pintle at
the point where the fuel enters the pintle chamber.
Exercise care when handling fuel injectors during service. Be careful not
to lose the pintle cap and replace O-rings to assure a tight seal. Never
apply direct battery voltage to test a fuel injector.
Стр . 1 из 44 SEQUENTIAL ELECTRONIC FUEL INJECTION (SEFI)
18.11.2005 http://www.chiltondiy.com/content/8687/8687_5_4.html