4-12
Chapter
4
Fuel and exhaust systems
1 1 Fuel injection system
-
general information
QUICK-CONNECT FITTINGS
Fuel-injected vehicles are equipped with either a Throttle Body In-
jection
system (four-cylinder engine) or a Multi-Point lnjection
system
six-cylinder engine). Both systems use an Elec-
tronic Control Unit
to control pulse width.
The pulse width is the period of time during which the injector is
energized (squirts fuel). The Electronic Control Unit
opens and
closes the injector's ground path to control fuel injector pulse width
and thus meter the amount of fuel available to the engine. By continually
altering the pulse width, the ECU adjusts the air-fuel ratio for varying
operating conditions. For more information about the ECU, see Chap-
ter 6.
Throttle body injection
is a single-point system that injects fuel
through one electrically operated fuel injector into the throttle body
above the throttle plate.
Multi-Point lnjection
is a multi-injector, sequential system: Fuel
is iniected into the intake manifold
of each intake valve in
metered amounts through electrically operated injectors. The
injectors are energized in a specific sequence by the Electronic Control
Unit
There is no injector in the throttle body itself, as in a TBI
system; the six injectors are installed in the intake manifold. They
receive pressurized fuel from a fuel rail attached to their upper ends.
System fuel pressure on both systems is provided by an in-tank elec-
tric fuel pump and is controlled by a spring and vacuum-assisted fuel
pressure regulator.
12 Fuel lines and fittings
-
inspection and replacement
Warning: Gasoline is extremely flammable, so extra precautions must
be taken when working on any part of the fuel system. Don't smoke
or allow open flames or bare light bulbs in or near the work area. Also,
don't work in a garage where a natural gas appliance such as a water
heater or clothes dryer is present.
Inspection and replacement
Refer to illustration 12.6
1
Check the fuel lines and all fittings and connections for cracks,
leakage and deformation.
2
Check the fuel tank vapor vent system hoses and connections for
looseness, sharp bends and damage.
3
Check the fuel tank for deformation, cracks, fuel leakage and tank
band looseness.
4
Check the filler neck for damage and fuel leakage.
5
Repair or replace any damaged or deteriorated hoses or lines. If
your vehicle is equipped with fuel injection, see below for information
on replacing fuel line fittings.
6
When attaching hoses t o metal lines, overlap them as shown (see
illustration).
HOSE
I
12.6 When attaching
a
section of rubber fuel hose t o
a
metal
fuel line, be sure t o overlap the hose as shown and secure
it
t o
the line w i t h
a
new hose clamp of the proper type
Typical under body quick-connect fittings
equipped vehicle)
Quick-connect fitting locations (MPI-equipped vehicle)
Fuel line fitting replacement
injected vehicles)
Refer to illustrations
12. 10, 12.13 and 12. 14
7
Remove the fuel tank filler cap t o relieve fuel tank pressure.
8
If the vehicle is equipped with Multi Point lnjection
relieve
the system pressure before proceeding (see Section
2).
If the vehicle
is equipped with Throttle Body lnjection
system pressure is bled
off when the fuel pump is not operating
you can disconnect fuel
hoses and lines as soon as you have turned off the engine.
9
All fuel injected engines use special quick-connect fuel line fittings.
On TBI-equipped vehicles, the fittings are located at the throttle body
ends of the nylon reinforced hoses which connect the throttle body
to the fuel supply and return lines and under the vehicle along the left
frame rail (see illustration). On MPI-equipped engines, they're located
at the fuel rail inlet port and at the connection between the fuel return
line and the fuel return hose (see illustration).
10 The fittings consist of t w o O-rings, a spacer between the t w o
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