1991 1999 ford explorer chilton User Manual

							
SPECIFICATION CHARTS
IAT and ECT sensor specifications chartClick to enlarge
Chilton® Automotive Information Systems. © 2004 Thomson Delmar Learning.
SPECIFICATION CHARTS 599 
						

							
BASIC FUEL SYSTEM DIAGNOSIS
When there is a problem starting or driving a vehicle, two of the most important checks involve the ignition
and the fuel systems. The questions most mechanics attempt to answer first, is there spark? and is there
fuel? will often lead to solving most basic problems. For ignition system diagnosis and testing, please refer to
the information on engine electrical components and ignition systems found earlier in this manual. If the
ignition system checks out (there is spark), then you must determine if the fuel system is operating properly
(is there fuel?).
Chilton® Automotive Information Systems. © 2004 Thomson Delmar Learning.
BASIC FUEL SYSTEM DIAGNOSIS 601 
						

							
FUEL LINES AND FITTINGS
General Information
Quick-connect (push type) fuel line fittings must be disconnected using proper procedure or the fitting
may be damaged. There are two types of retainers used on the push connect fittings. Line sizes of  3
/8
and  5
/16  in. diameter use a hairpin clip retainer. The  1
/4  in. diameter line connectors use a duck-bill clip
retainer. In addition, some engines use spring-lock connections, secured by a garter spring, which
require Ford Tool T81P-19623-G (or equivalent) for removal.
Hairpin Clip Fitting
REMOVAL & INSTALLATION Clean all dirt and grease from the fitting. Spread the two clip legs about  1
/8  in. (3mm) each to
disengage from the fitting and pull the clip outward from the fitting. Use finger pressure only; do not
use any tools.
1. 
Grasp the fitting and hose assembly and pull away from the steel line. Twist the fitting and hose
assembly slightly while pulling, if the assembly sticks.
2. 
Inspect the hairpin clip for damage, replacing the clip if necessary. Reinstall the clip in position on the
fitting.
3. 
Inspect the fitting and inside of the connector to ensure freedom from dirt or obstruction. Install the
fitting into the connector and push together. A click will be heard when the hairpin snaps into the
proper connection. Pull on the line to insure full engagement.
4. 
FUEL LINES AND FITTINGS 603 
						

							Hairpin clip fuel fitting installation
Click to enlarge
HOW TO USE THIS BOOK
604 REMOVAL & INSTALLATION 
						

							Exploded views of the hairpin and duckbill clip type fuel fittings
Click to enlarge
Duckbill Clip Fitting
REMOVAL & INSTALLATION A special tool is available from Ford and other manufacturers for removing the retaining clips. Use
Ford Tool T82L-9300-AH or equivalent. If the tool is not on hand, go onto step 2. Align the slot on
the push connector disconnect tool with either tab on the retaining clip. Pull the line from the
connector.
1. 
If the special clip tool is not available, use a pair of narrow 6-inch slip-jaw pliers with a jaw width of
0.2 in (3mm) or less. Align the jaws of the pliers with the openings of the fitting case and compress
the part of the retaining clip that engages the case. Compressing the retaining clip will release the
fitting, which may be pulled from the connector. Both sides of the clip must be compressed at the
same time to disengage.
2. 
Inspect the retaining clip, fitting end and connector. Replace the clip if any damage is apparent.
3. 
Push the line into the steel connector until a click is heard, indicating the clip is in place. Pull on the
line to check engagement.
4.  HOW TO USE THIS BOOK
Duckbill Clip Fitting 605 
						

							Duckbill clip fuel fitting installation
Click to enlarge
Spring Lock Coupling HOW TO USE THIS BOOK
606 REMOVAL & INSTALLATION 
						

							
REMOVAL & INSTALLATION
The spring lock coupling is held together by a garter spring inside a circular cage. When the coupling is
connected together, the flared end of the female fitting slips behind the garter spring inside the cage of the
male fitting. The garter spring and cage then prevent the flared end of the female fitting from pulling out of
the cage. As an additional locking feature, most vehicles have a horseshoe-shaped retaining clip that
improves the retaining reliability of the spring lock coupling.
Spring lock fitting removal and installation proceduresClick to enlarge
HOW TO USE THIS BOOK
REMOVAL & INSTALLATION 607 
						

							Spring lock horseshoe-shaped retaining clip installation
Click to enlarge
Chilton® Automotive Information Systems. © 2004 Thomson Delmar Learning. HOW TO USE THIS BOOK
608 REMOVAL & INSTALLATION 
						

							
SEQUENTIAL FUEL INJECTION (SFI) SYSTEM
General Information
The Sequential Fuel Injection (SFI) system includes a high pressure, inline electric fuel pump mounted in the
fuel tank, a fuel supply manifold, a throttle body (meters the incoming air charge for the correct mixture with
the fuel), a pressure regulator, fuel filters and both solid and flexible fuel lines. The fuel supply manifold
includes 4, 6 or 8 electronically-controlled fuel injectors, each mounted directly above an intake port in the
lower intake manifold. Each injector fires once every other crankshaft revolution, in sequence with the engine
firing order.
The fuel pressure regulator maintains a constant pressure drop across the injector nozzles. The regulator is
referenced to intake manifold vacuum and is connected in parallel to the fuel injectors; it is positioned on the
far end of the fuel rail. Any excess fuel supplied by the fuel pump passes through the regulator and is returned
to the fuel tank via a return line.
The pressure regulator reduces fuel pressure to 39-40 psi under normal operating conditions. At idle or
high manifold vacuum condition, fuel pressure is further reduced to approximately 30 psi.
The fuel pressure regulator is a diaphragm-operated relief valve, in which the inside 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 Powertrain Control
Module (PCM), although electrical power is routed through the fuel pump relay and an inertia switch. The
fuel pump relay is normally located in the power distribution box, under the hood, and the inertia switch is
located on the toe-board, to the right of the transmission hump, in the passenger-side footwell. The inline
fuel pump is usually mounted in the fuel tank. Tank-mounted pumps can be either high- or low-pressure,
depending on the model.
The inertia switch opens the power circuit to the fuel pump in the event of a collision. Once tripped, the
switch must be reset manually by pushing the reset button on the assembly.
Check that the inertia switch is reset before diagnosing power supply problems to the fuel pump.
The fuel injectors used with SFI system are electro-mechanical (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 and allow 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
always replace O-rings to assure a tight seal. Never apply direct battery voltage to test a fuel injector.
The injectors receive high-pressure fuel from the fuel supply manifold (fuel rail) assembly. The complete
assembly includes a single, pre-formed tube with four, six or eight connectors, the mounting flange for the
pressure regulator, mounting attachments to locate the manifold and provide the fuel injector retainers and a
Schrader® quick-disconnect fitting used to perform fuel pressure tests.
The fuel manifold is normally removed with the fuel injectors and pressure regulator attached. Fuel injector
electrical connectors are plastic and have locking tabs that must be released when disconnecting the wiring
SEQUENTIAL FUEL INJECTION (SFI) SYSTEM 609 
						

							
harness.
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 vehicles fuel system components can be accomplished safely and effectively by
adhering to the following rules and guidelines.
To avoid the possibility of fire and personal injury, always disconnect the negative battery cable
unless the repair or test procedure requires that battery voltage by applied.
· 
Always relieve the fuel system pressure prior to disconnecting any fuel system component (injector,
fuel rail, pressure regulator, etc.) fitting or fuel line connection. Exercise extreme caution whenever
relieving fuel system pressure to avoid exposing skin, face and eyes to fuel spray. Please be advised
that fuel under pressure may penetrate the skin or any part of the body that it contacts.
· 
Always place a shop towel or cloth around the fitting or connection prior to loosening to absorb any
excess fuel due to spillage. Ensure that all fuel spillage is quickly remove from engine surfaces.
Ensure that all fuel-soaked cloths or towels are deposited into a flame-proof waste container with a
lid.
· 
Always keep a dry chemical (Class B) fire extinguisher near the work area.
· 
Do not allow fuel spray or fuel vapors to come into contact with a spark or open flame.
· 
Always use a second wrench when loosening or tightening fuel line connections fittings. This will
prevent unnecessary stress and torsion to fuel piping. Always follow the proper torque specifications.
· 
Always replace worn fuel fitting O-rings with new ones. Do not substitute fuel hose where rigid pipe
is installed.
· 
Relieving Fuel System Pressure
All SFI fuel injected engines are equipped with a pressure relief valve located on the fuel supply manifold.
Remove the fuel tank cap and attach fuel pressure gauge T80L-9974-B, or equivalent, to the valve to release
the fuel pressure. Be sure to drain the fuel into a suitable container and to avoid gasoline spillage. If a pressure
gauge is not available, disconnect the vacuum hose from the fuel pressure regulator and attach a hand-held
vacuum pump. Apply about 25 in. Hg (84 kPa) of vacuum to the regulator to vent the fuel system pressure
into the fuel tank through the fuel return hose. Note that this procedure will remove the fuel pressure from the
lines, but not the fuel. Take precautions to avoid the risk of fire and use clean rags to soak up any spilled fuel
when the lines are disconnected.
An alternate method of relieving the fuel system pressure involves disconnecting the inertia switch. Follow
the procedures outlined later in this Section. HOW TO USE THIS BOOK
610 General Information