Pontiac Fiero 1988 Service Manual page 534

DRIVEABILITY AND EMISSIONS - FUEL INJECTION (TBI) 6E2-C2-3
BASIC SYSTEM OPERATION
The fuel control system (Figure C2-2) has an
electric fuel pump, located in the fuel tank with the
gage sending unit, which pumps fuel to the TBI
through the fuel supply line , then through an in-line
fuel filter. The pump is designed to provide
pressurized fuel at about 125 kPa (18 psi). A pressure
regulator in the TBI keeps fuel available to the
injector at a constant pressure between 62 and 90 kPa
(9 and 13 psi). Fuel in excess of injector need is
returned to the fuel tank by a separate line.
The ECM controls the injector, located in the fuel
meter body assembly of the TBI. The injector delivers
fuel in one of several modes, as described above.
In order to properly control the fuel supply, the
fuel pump is operated by the ECM through the fuel
pump relay and oil pressure switch (see Fuel Pump
Electrical Circuit).
THROTTLE BODY INJECTION (TBI) UNIT
The Model 700 TBI unit (Figure C2-3) is made up
of two major casting assemblies:
1. A fuel meter body with:
• A fuel meter assembly, including a pressure
regulator
• A fuel injector
2. A throttle body with:
• A throttle valve
• An idle air control (IAC) valve
• A throttle position sensor (TPS).
The throttle body portion of the TBI unit may
contain ports located above, or below the throttle
valve. These ports generate the vacuum signals for
the exhaust gas recirculation (EGR) valve, MAP
sensor, and the canister purge system.
Fuel Injector
The fuel injector (Figure C2-4) is a solenoid
operated device controlled by the ECM. The ECM
turns on the solenoid, which lifts a normally closed
ball valve off a seat. The fuel, under pressure, is
injected in a conical spray pattern at the walls of the
throttle body bore above the throttle valve. The fuel
which is not needed by the injector passes through the
pressure regulator before being returned to the fuel
tank.
A fuel injector which does not open may cause a
no-start condition. An injector which is stuck partly
open could cause loss of pressure after engine
shutdown, so long crank times would be noticed on
some engines. Also, dieseling could occur because
some fuel could be delivered to the engine after the
key is turned "OFF."
F U E L I N J E C T O R A S S E M B L Y
T H R O T T L E P O S I T I O N S E N S O R ( T P S )
paH
T H R O T T L E B O D Y A S S E M B L Y
[TJ
T U B E M O D U L E A S S E M B L Y
[ T l
I D L E A I R C O N T R O L (IAC) V A L V E
FUEL
M E T E R A S S E M B L Y
I T ]
P R E S S U R E R E G U L A T O R
C O V E R A S S E M B L Y
8P 091 O A S
1/15/87
Figure C2-3 - Model 700 TBI
HI
B
H
G O
H
B
EE
B
FUEL INLET
FUEL OUTLET
F U E L I N J E C T O R
F U E L M E T E R A S S E M B L Y
PURGE F I L T E R
INLET F I L T E R
T H R O T T L E B O D Y A S S E M B L Y
P R E S S U R E R E G U L A T O R C O V E R A S S E M B L Y
P R E S S U R E R E G U L A T O R S P R I N G
P R E S S U R E R E G U L A T O R D I A P H R A G M
A S S E M B L Y
BP 0330-SY
1/15/87
Figure C2-4 - TBI 700 Fuel Metering System