Pontiac Fiero 1988 Service Manual page 373

6C-2 FUEL SYSTEM
Any time fuel system is being worked on,
always
keep
a
dry
chemical
(Class
B)
fire
extinguisher near the work area.
FUEL SYSTEM
All gasoline engines are designed to use only
unleaded gasoline. Unleaded gasoline must be used for
proper emission control system operation. Its use will
also minimize spark plug fouling and extend engine oil
life. Using leaded gasoline can damage the emission
control system and could result in loss of emission
warranty coverage.
FUEL METERING
Throttle Body Injection (TBI)
With Throttle Body Injection (TBI), an injection
unit is placed on the intake manifold where the
carburetor is normally mounted. The TBI unit is
computer controlled and supplies the correct amount
of fuel during all engine operating conditions. See
Section 6E for information relative to operation and
diagnosis of TBI units.
Multi Port Fuel Injection (MPFI)
The ECM is in complete control of this fuel
delivery system during all driving conditions,
The intake manifold function, like that of a diesel,
is used only to let air into the engine. The fuel is
injected by separate injectors that are mounted near the
intake valve.
The ECM monitors all the vehicle functions, as
in the carbureted or TBI system.
With Multi Port Injection System, there is no
need for a thermae, EFE, barosensor, A.I.R. system or
dual bed converter. This sytem provides better cold
driveability, less exhaust emissions and a better throttle
response.
Two interchangeable O rings are used on the
injector that must be inspected when the injectors are
removed. Check O rings for cuts or other types of
damage and replace as necessary.
The air cleaner is remotely mounted. It is
connected to the throttle body by air intake ducting.
The intake manifold is of a totally new design, as
it is only used to pass air. It is tuned and offers vehicle
performance improvement.
The throttle body design is very simple as it
handles only air. It also utilizes an integral idle air
control unit to govern idle speed and a throttle position
sensor (TPS). The I AC and TPS are both controlled by
the ECM.
See Figure 1
Electric Fuel Pump
The electric fuel pump is attached to the bottom
of the fuel sending unit.
See Figure 2
From the pump, fuel passes through an in-line
fuel filter to the TBI or fuel rail. To control fuel pump
operation, a fuel pump relay is used.
When the ignition switch is turned to the "ON"
position, the fuel pump relay activates the electric fuel
pump for 1.5 to 2.0 seconds to prime the injector(s). If
the ECM does not receive reference pulses from the
distributor after this time, the ECM signals the relay
to turn the fuel pump off. The relay will once again
activate the fuel pump when the ECM receives
distributor reference pulses.
FUEL PUMP RELAY
All Electronic Fuel Injection (EFI) engines use a
fuel pump relay. The EFI system relays are located on
left upper panel in the engine compartment as shown
in Figure 3.
FUEL FILLER CAP
The fuel tank filler neck is equipped with a screw
type cap. The threaded part of the cap requires several
turns counterclockwise to remove. The long threaded
area was designed to allow any remaining fuel tank
pressure to escape during the cap removal operation.
A built-in torque limiting device prevents over-
tightening. To install, turn the cap clockwise until a
clicking noise is heard. This signals that the correct
torque has been reached and the cap is fully seated.
N O T I C E :
If a fuel filler cap requires replacement,
only a cap with the same features should be used.
Failure to use the correct cap can result in a serious
malfunction of the system.
FUEL TANK
The fuel tank is located under the middle of the
vehicle.
The tank is held in place by two metal straps,
hinged (with a bolt through the hinge) and secured at
the opposite end with a nut and bolt assembly.
See Figure 4
Anti-squeak pieces are used on top of the tank to
reduce rattles and other annoying noises.
FUEL GAGE SENDER
The fuel gage sending unit is attached to the top
of the fuel tank. It is held in place with a cam lock ring
and a gasket is used between the tank and sending unit.
Some sending units have two and others have
three places to attach hoses. One line is for the fuel feed
line. The second line is connected to the vapor canister,
to keep fuel vapor from getting into the air (see Section
6E). The third line is a fuel return line to the tank.
FUEL MSP VAPOR P I P E S
The fuel feed and return pipes extend from the
fuel gage sending unit to the engine compartment. The
pipes are secured to the underbody with clip and screw
assemblies. Both fuel feed pipes must be properly
routed and retained, and should be inspected