1988 PONTIAC FIERO Service Repair Manual

6E3-C2-2 5.OL (VIN F) & 5.7L(VIN 8) DRIVEABILITY AND EMISSIONS
MODES OF OPERATION
The ECM looks at voltages from several sensors to
determine how much fuel to give the engine. The fuel
is delivered under one of several conditions, called
"modes". All the modes are controlled by the ECM
and are described below.
Starting Mode
When the ignition is first turned "ON", the ECM
will turn "ON" the fuel pump relay for two seconds,
and the fuel pump will build up pressure. The ECM
then checks the coolant temperature sensor, throttle
position sensor, and determines the proper airlfuel
ratio for starting. This ranges from 1.5
: 1 at -36°C
(-33°F) to 14.7:l at 94°C (201°F). The ECM controls
the amount of fuel delivered in the starting mode by
changing how long the injectors are pulsed "ON".
The cold start valve
(Figure C2-2), not controlled
by the ECM, is used to provide additional fuel during
the starting mode to improve cold start-ups. This
circuit is important, when the engine coolant
temperature is very low, because the other injectors
would not be pulsed "ON" long enough to provide the
needed amount of fuel to start. The cold start valve is
somewhat different from the other injectors in that it
causes the fuel to be vaporized for a better combustible
mixture.
The circuit is activated only in the crank mode.
The power is supplied directly from the starter
solenoid and is protected by the crank fuse. The
system is controlled by a cold start fuel injection
switch which provides a ground path for the valve
during cranking whenever engine coolant is below
35"
C (95°F).
100 VALVE - COLD START
101 TUBE AND BODY ASSEMBLY
102 O-RING SEAL
- VALVE
103 O-RING SEAL
- BODY
104 O-RING SEAL -TUBE
The cold start fuel injection switch contains a
bimetal switch which opens the circuit at specified
coolant temperature. This bimetal is also heated
by
the winding in the switch, which would allow the
valve to stay "ON" 8 seconds at
-20" C or below. The
time the switch stays closed varies inversely with
coolant temperature. In other words, as the coolant
temperature goes up the maximum cold start valve
"ON" time goes down.
Clear Flood Mode
If the engine floods, clear it by pushing the
accelerator pedal down all the way. The ECM then
pulses the injectors at an airlfuel ratio of
20:l. The
ECM holds this injector rate as long as the throttle
stays wide open, and the engine rpm is below 600.
If
the throttle position becomes less than 80%, the ECM
returns to the starting mode.
Run Mode
The RUN mode has two conditions called "Open
Loop" and "Closed Loop".
When the engine is first started, and rpm is above
400 rpm, the system goes into "Open Loop" operation.
In "Open Loop", the ECM will ignore the signal from
the Oxygen
(Oz) sensor, and calculate the airlfuel
ratio based on inputs from the coolant and MAF
sensors.
The system will stay in
"Open Loop" until the
following conditions are met:
1. The O2 sensor has varying voltage output,
showing that it is hot enough to operate properly.
(This depends on temperature.)
2. The coolant sensor is above a specified
temperature about 40°C
(104°F).
3. A specific amount of time has elapsed after
starting the engine.
The specific values for the above conditions vary
with different engines, and are stored in the mem-cal.
When these conditions are met, the system goes into
"Closed Loop" operation. In "Closed Loop", the ECM
will calculate the airlfuel ratio (injector on-time)
based on the signal from various sensors but
mainly
the O2 sensor. This allows the air 1 fuel ratio to stay
very close to 14.7: 1
.
Acceleration Mode
The ECM looks at rapid changes in throttle
position and air flow, and provides extra fuel.
Figure C2-2 Cold Start Valve

DRIVEABILITY AND EMISSIONS 5.OL (VIN F) & 5.7L (VIN 8) 6E3-CZ-3
Deceleration Mode
The ECM looks at changes in throttle position and
air flow to reduce the amount of fuel. When
deceleration is very fast, the ECM may shut off fuel
completely for short periods.
Battery Voltage Correction Mode
When battery voltage is low, the ECM can
compensate for the weak spark delivered by the
distributor by:
@ Increasing the amount of fuel delivered;
@ Increasing the idle rpm; and
@ Increasing ignition dwell time.
Fuel Cutoff Mode
No fuel is delivered by the injector when the
ignition is "OFF". This prevents dieseling. Also, fuel
is not delivered if no reference pulses are seen from
the distributor, which means the engine is not
running. This prevents flooding.
FUEL CONTROL SYSTEM
Basic System Operation
The fuel system (Figure C2-3) starts with the fuel
in the fuel tank.
An electric fuel pump, located in the fuel tank with
the gage sending unit, pumps
fuel to the fuel rail
through an in-line fuel filter. The pump is designed to
provide fuel at a pressure above the pressure needed
by the injectors. A pressure regulator in the fuel rail
keeps fuel available to the injectors at
a constant
pressure, depending on manifold pressure. Unused
fuel is returned to the fuel tank by a separate line. For
further information on the fuel tank, in-line filter, and
fuel lines, see Section
"6C".
The injectors are controlled by the ECM. They
deliver 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 Code
54).
Throttle Body Unit
The throttle body has a throttle valve to control
the amount of air delivered to the engine. The TPS
and the IAC valve are also mounted on the throttle
body. The throttle body contains vacuum ports located
at, above, or below the
throttIe valve. 'I'hese ports
generate the vacuum signals
needed I,y v~irious
Figure C2-3 Fuel System
components. Engine coolant is directed through the
coolant cavity, on the bottom of the throttle body, to
warm the throttle valve and prevent icing.
Fuel Rail
The fuel rail is mounted to the top of the engine. It
distributes fuel to the individual injectors. Fuel is
delivered to the input end of the rail by the fuel lines,
goes through the rail, then to the pressure regulator.
Remaining fuel is then returned to the fuel tank.
Fuel Injectors
The fuel injector is a solenoid operated device
controlled by the ECM (see Figure
C2-4). The ECM
turns
"ON" the solenoid, which opens a valve to allow
fuel delivery.
The fuel, under pressure, is injected in a
conical spray pattern at the opening of the intake
valve. The fuel, which is not used by the injectors,
passes through the pressure regulator before being
returned to the fuel tank.
An injector which is stuck partly open will cause
loss of pressure after engine shut down, 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 ignition is turned
"OFF".

6E3-CZ-4 5.OL (VIN F) & 5.7L(VIN 8) DRIVEABILITY AND EMISSIONS
FUEL INJECTOR
1 INTAKE MANIFOLD
( INTAKE VALVE
1 ELECTRICAL TERMINAL
Figure C2-4 Fuel Injector
Pressure Regulator
The pressure regulator is a diaphragm-operated
relief valve with injector pressure on one side and
manifold pressure on the other. The function of the
regulator is to maintain a constant pressure at the
injector at all times. The pressure regulator
cotnpensates for engine load by increasing fuel
pressure when it sees low engine vacuum.
The pressure regulator is mounted on the fuel rail,
and is serviced separately.
If the pressure
is too low, poor performance could
result. If the pressure is too high, excessive odor and a
Code
45 may result. CHART A-7 has information on
diagnosing fuel pressure conditions.
Idle Air Control (IAC) Valve
The purpose of the idle air control (IAC) valve
(shown in Figure
C2-5) is to control engine idle speed,
while preventing stalls due to changes in engine load.
The IAC valve, mounted in the throttle body,
controls bypass air around the throttle
valve. Hy
moving a conical valve IN (to decrease air flow) or
OUT (to increase air flow), a controlled amount of air
can move around the throttle plate. If rpm is too low.
more air
is bypassed around the throttle valve to
increase rpm. If
rpm is too high, less air is bypassed around the
throttle valve to decrease rpm.
The IAC valve moves in small steps called
"counts", which can be monitored by a "Scan" tool.
During idle, the proper position of the IAC valve is
calculated by the ECM based on battery voltage,
coolant temperature, and engine rpm. If the rpm
drops below
a specified rpm, and the throttle plate is
closed, the ECM senses a near stall condition. The
ECM will then calculate a new valve position to
prevent stalls.
If the IAC valve is disconnected and reconnected
with the engine running, the idle rpm may be wrong.
In this case, the IAC valve can be reset by starting the
engine momentarily and then turning the ignition
"OFF
".
When servicing the IAC, it should only be
disconnected or connected with the ignition "OFF".
This will keep from having to reset the IAC.
The IAC valve affects only the idle characteristics
of the vehicle. If it is open fully, too much air will be
allowed into the manifold and idle speed will be high.
If it is stuck closed, too little air will be allowed in the
manifold, and idle speed will be too low. If it is stuck
part way open, the idle may be rough, and will not
respond to engine load changes.
Different designs are used for the IAC valve. Be
sure to use the correct design when replacement is
required.
SINGLE TAPER VALVE
DUAL TAPER VALVE
BLUNT
PINTLE
Figure C2-5 IAC Valve Designs

DRIVEABILITY AND EMISSIONS 5.OL (VIN F) & 5.7L (VIN 8) 6E3-C2-5
Fuel Pump Electrical Circuit
When the ignition is first turned "ON", without
the engine running, the ECM will turn the fuel pump
relay "ON" for two seconds.
This builds up the fuel
pressure quickly. If the engine is not started within
two seconds, the ECM will shut the fuel pump "OFF"
and wait until the engine is cranking. As soon as the
engine is cranked, the ECM will turn the relay "ON"
and run the fuel pump.
As
a backup system to the fuel pump relay, the
fuel pump can also be turned "ON" by the oil pressure
switch. The oil pressure switch is a normally open
switch which closes when oil pressure reaches about
28
kPa (4 psi). If the fuel pump relay fails, the oil
pressure switch will close, and run the fuel pump.
An inoperative fuel pump relay can result in long
cranking times, particularly if the engine is cold but
should result in
a Code 54.
An inoperative fuel pump would cause a no start
condition. A fuel pump which does not provide enough
pressure can result in poor performance.
DIAGNOSIS
FUEL CONTROL SYSTEM
Some failures of this system will result in an
"Engine Cranks But Won't Run". If
this condition
exists see CHART A-3. This chart will determine if
the problem is caused by the ignition system, ECM, or
fuel pump circuit. If
it's determined to be a fuel
problem CHART A-7 will be used. This includes the
injectors, pressure regulator, fuel pump, and fuel
pump relay. The fuel system wiring schematic is
covered on the facing page of Code CHART 54.
If a malfunction occurs in the fuel control system,
it usually results in either a rich or
a lean exhaust
condition. This condition is sensed by the oxygen
sensor and the ECM will change the fuel calculation
(injector pulse width) based on the
O2 sensor reading.
The change
made to the fuel calculation will be
indicated by a change in the block learn values, which
can be monitored by a "Scan" tool.
The normal block
learn values are around 128, and if the
O2 sensor is
sensing a lean condition, the EC
M will add fuel which
will result in a block learn value above 128.
If the O2
sensor is sensing a rich exhaust the ECM will reduce
fuel to the engine and this will result in block learn
values below 128. Some variations in block
learn
values are normal because all engines are not exactly
the same. However, if the block learn values are
+ 10
counts from 128 a system problem exists. If the block
learn values are greater than 138 see Code 44, for
items which can cause a lean system.
If the block learn values are less than 118 see Code
45 for items which can cause the system to run rich. If
a driveability symptom exists, refer to the
particular symptom in Section
"B" for additional
items to check.
IDLE AIR CONTROL VALVE
AUScan" tool will read IAC position in steps (counts).
"0" steps indicates the ECM is commanding the IAC to
be driven all the way in, to a fully seated position, and
this is usually caused by a vacuum leak. The higher
the number of counts the more air being allowed to
pass the IAC valve. CHART C-2C can be used to
diagnosis the IAC valve. Also refer to "Rough,
Unstable, or Incorrect Idle, Stalling" in symptoms,
Section "B" for other possibilities for the cause
of idle
problems.
FUEL SYSTEM PRESSURE TEST
A fuel system pressure test is part of several of the
diagnostic charts and symptom checks. To perform
this test, use the procedure in CHART A-7.
ON-CAR SERVICE
PORT FUEL INJECTION COMPONENTS
CAUTION:
Before servicing an injector, fuel
rail, or pressure regulator,
it is
necessary to relieve the pressure in
the fuel system, to minimize the
risk of fire and personal injury.
(See "Fuel Pressure Relief
Procedure" below). To reduce the
chance of personal injury, cover
the fuel line with
a shop cloth to
collect the fuel, and then place the
cloth in an approved container.
FUEL PRESSURE RELIEF PROCEDURE
1. Connect fuel gage J 34730-1 or equivalent to fuel
pressure valve. Wrap a shop towel around fitting
while connecting gage to avoid spillage.
2. Install bleed hose into an approved container and
open valve to bleed system pressure.
Plenum
(Figure
C2-6)
Remove or Disconnect
1. Negative battery cable.
2. Throttle, 'F.V., and cruise control cable.
3. Cable retaining bracket.
4.
'I'hrottle body retaining bolts (4).
5. 'L'l'S and IAC valve electrical connectors.
6. Vacuum hoses.

6E3-C2-6 5.OL (VIN F) & 5.7L(VIN 8) DRIVEABILITY AND EMISSIONS
PLENUM BOLTS TIGHTEN TO 25 N m (19 LB. FT.)
Figure C2-6
7. Right runners.
8. Plenum retaining bolts.
9. Plenum and gaskets (discard gaskets).
Install or Connect
1. New gaskets.
2. Reverse removal procedures. See Figure C2-6 for
bolt torque specifications.
FUEL RAIL ASSEMBLY
Fuel Rail (Figure C2-7)
n Remove or Disconnect
1. Negative battery cable
2. Fuel system pressure following "Fuel Pressure
Relief procedure".
3. Plenum. (Refer to Plenum Removal).
4. Cold start valve line.
5. Runners.
6. Cold start valve.
7. Fuel lines and injector harness connectors.
8. Loosen rail retaining bolts and raise rail.
9. Rail and injectors.
10. Injector O-ring seal (86) (Figure C2-9) from each
injector spray tip and discard.
) 06 22 84 PRESSURE REGULATOR 5s 1821SE I
Figure C2-7 Fuel Rail Assembly Identification
Install or Connect
1. New injector O-rings.
2. Coat injector O-rings with engine oil.
3. Reverse removal instructions.
Refer to Figure C2-7 for torque specifications.

DRIVEABILITY AND EMISSIONS 5.OL (VIN F) & 5.7L (VIN 8) 6E3-C2-7
Figure C2-8 Fuel Rail Pressure Regulator
FUEL RAIL SERVICE
IDENTIFICATION
An eight digit identification number is stamped
on the fuel rail assembly, as shown in Figure C2-8.
Refer to this model identification number if servicing
or part replacement is required.
Names of component parts will be found on the
numbered list that accompanies the dis-assembled
view, (Figure C2-9). Numbers used to identify parts
there will be used to identify the same parts in other
illustrations of this section of the manual.
UNIT SERVICE PROCEDURES
lrnportant
When servicing the fuel rail assembly,
precautions must be taken to prevent dirt and
other contaminants from entering the fuel
passages. It is recommended that fittings be
capped, and holes
be plugged during servicing.
Important
At any time the fuel system is opened for service,
the
O-ring seals ised with the related
component(s) should be replaced.
Cleaning and Inspection
Before disassembly, the fuel rail assenlbly may be
cleaned with a spray type engine cleaner, such as
AC
Delco X-30A or equivalent, following
package
instructions. The fuel rail should not be immersed in
liquid solvent.
0 VALVE - COLD START
101 TUBE AND BODY ASSEMBLY
102 O-RING SEAL
- VALVE
103 O-RING SEAL
- BODY
104 O-RING SEAL -TUBE
Figure CZ-10 Cold Start Valve Assembly
COLD START TUBE AND VALVE ASSEMBLY
(Figure
CZ-I 0)
Remove or Disconnect
1. Negative battery cable. -
Relieve fuel system pressure, following "Fuel
Pressure Relief Procedure".
Plenum, per previous instructions.
Brake booster line.
Tube and body assembly (101) at fitting on fuel
rail.
Electrical connector from cold start valve (100).
PVC hose.
Cold start valve retaining bolt.
Cold start valve assembly from fuel rail and
intake manifold.
+$ Disassemble
1. Raise tab on tube and body assembly (101) to clear
electrical connector and unscrew cold start valve
(100).
2. O-ring seals (102, 103, and 104) from tube and
body assembly
(lOl), cold start valve (loo), and
fuel rail fitting. Discard seals.
1. Lubricate
new O-ring seals (102, 103, and 104)
with engine oil and install at following locations:
@ O-ring seal (102) goes on end of cold start
valve
(100).
@ O-ring seal (103) goes inside body of tube and
body assembly
(101).
@ O-ring seal (104) goes up against collar of tube
and body assembly.

6E3-CZ-8 5.OL (VIN F) & 5.7L(VIN 8) DRIVEABILITY AND EMISSIONS
F~gure C2-9 Fuel Rail Assembly

DRIVEABILITY AND EMISSIONS 5.OL (VIN F) & 5.7L (VIN 8) 6E3-CZ-9
Cold start valve (100) onto tube and body
assembly
.
Screw in until valve bottoms. then back off
until hole in mounting lug on valve will be
aligned properly with hole in fuel rail when
mounted
.
@ Bend tang over cold start valve to lock it in
position
.
Clean
@ Areas around valve and connection with AC
Delco X-30A or equivalent
.
Install or Connect
1 . Cold start (100) valve in intake manifold .
2 . Cold start valve retaining bolt .
Tighten
@ Retaining bolt to 27 Nwm (20 ft . lbs.). .
3 . PVC hose .
4 . Tube and body assembly (101) at fitting on fuel
rail
.
Tighten
@ Nut on fitting to 27 N-m (20 ft . lbs.).
6 . Brake booster line .
6 . Electrical connector on cold start valve (100)
7 . Negative battery cable .
Inspect
@ Energize fuel pump and inspect for leaks .
8 . Intake manifold plenum. per previous
instructions
.
FUEL RAIL SERVICE
FIGURE CZ-9
PARTS INFORMAION
PART NAME PART #
. .................. O-ring Fuel Inlet Line 1
. ................ O-ring Fuel Return Line 2
Assembly
. Fuel Pressure Connection ....... 26
Seal
. Fuel Pressure Connection ........... 27
Cap
. Fuel Pressure Connection ............ 28
Injector
. Port ......................... 85
. . .................. Seal 0-Ring Injector 86
. .................. Clip Injector Retainer 87
. ..................... Valve Cold Start 100
Assembly
. Tube & Body 101 Seal .
....................... O-ring Valve 102
. . .................... Seal 0-Ring Body 103
. . .................... Seal 0-Ring Tube 104
. .......... Assembly Fuel Rail & Plug (LH) 200
. .......... Assembly Fuel Rail & Plug (RH) 220
Stud Assembly
. Rear Bracket
......................... Attaching 222
Seal
. 0-Ring . Fuel Outlet Tube ........... 224
. ................. Tube Front Crossover 230
. . ........ Seal 0-Ring Fuel Crossover Tube 232
. .*............. Retainer Crossover Tube 234
...... . Screw Assembly Retainer Attaching 235
Assembly
. Pressure Regulator and
............................. Base 240
. ................ . Seal 0-Ring Connector 252
. ................. Connector Base to Rail 250
Bracket
. Pressure Regulator & Base
......................... Assembly 255
Screw Assembly
. Bracket to rail
......................... Attaching 256
Screw Assetnhly
. Bracket to Base
......................... Attaching 258
. .................. Tube Rear Crossover 265
. . ............ Seal 0-Ring Crossover Tube 267
........... . Retainer Rear Crossover Tube 270
....... . Screw Assembly Retainer to LH Rail 271
......... . Screw Assembly Retainer to Base 273
.......... . Screw Assembly Base to RH Rail 275