battery replacement PONTIAC FIERO 1988 Service User Guide

ENGINE FUEL 6C.3
a Fuel feed and return pipes are secured to the
underbody with clamps and screw assemblies.
The pipes should be inspected occasionally for
leaks, kinks or dents.
e Follow the same routing as the original pipe.
e Pipes must be properly secured to the frame to
prevent chafing. A minimum of 6 mm
(1/4")
clearance must be maintained around a pipe to
prevent contact and chafing.
MPFl Fuel Pipes
Due to the fact that fuel pipes are under high
pressure, these systems require special consideration for service.
Many feed and return pipes use screw couplings
with
"0" Rings. Any time these fittings are loosened
to service or replace components, ensure that:
a A backup wrench is used while loosening and
tightening the fitting.
e Check all "0" rings at fitting locations (if
applicable) for cuts or any damage and replace
any that appear worn or damaged.
e Use correct torque when tightening fittings.
If pipes are replaced always use original
equipment parts, or parts that meet GM
specifications.
Fuel and Vapor Hoses
NOTICE: Fuel and vapor hoses are specially
manufactured. If replacement becomes necessary,
it is important to use only replacement hoses
meeting GM Specification 6163-M. These hoses
are identified with the words "Fluoroelastomer"
on them. Hoses not so marked could cause early
failure, or fail to meet emission standards.
e Do not use rubber hose within 4" of any part of
the exhaust system, or within
10" of the catalytic
converter.
FUEL PUMP
The electric fuel pump is in the fuel tank. The
tank has an outlet for a vapor return system. Any vapor
which forms is returned to the fuel tank along with hot
fuel through a separate line. This greatly reduces any
possibility of vapor lock by keeping cool fuel from the
tank constantly circulating through the fuel pump.
FUEL PUMP RELAY
To control fuel pump operation, a fuel pump
relay is used.
When the ignition switch is turned to "RUN"
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 off the fuel pump. The relay will once again
activate the fuel pump when the
ECM receives
distributor reference pulses.
Fuel Filter
CAUTION: To reduce the risk of fire
and personal injury, it is necessary
to
relieve the fuel system pressure
before servicing fuel system
components. (See Fuel System
Pressure Relief.)
The inline filters can be found on the rear
crossmember of the vehicle. Always use a backup
wrench any time that the fuel filter is removed or
installed. Also make sure that a good
"0" Ring is used
at all screw couple locations. Torque on fittings is
30
N-m (22 lb. ft.).
FUEL TANK
The fuel tank is usually located under the rear of
the vehicle and a number of shapes and sizes are used
depending on the application.
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.
Anti-squeak pieces are used on top of the tank to
reduce rattles and other annoying noises.
The fuel tank, cap and lines should be inspected
for road damage, whch could cause leakage. Inspect
fuel cap for correct sealing and indications of physical
damage. Replace any damaged or malfunctioning
parts.
Before attempting service of any type on the fuel
tank, always
(1) remove negative battery cable from
battery, (2) place "no smoking" signs near work areas,
(3) be sure to have C02 fire extinguisher handy, (4)
wear safety glasses and
(5) siphon or pump fuel into an
explosion proof container.
Fuel Filler Gap
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 is designed to allow any remaining fuel
tank pressure to escape while the cap is being removed.
A built-in torque-limiting device prevents
overtightening. 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 OTI G E: If a fuel filler cap requires replacement,
use only a cap with the same features. Failure to
use the correct cap can result in a serious
malfunction of the system.
Available on some models is an electric locking
fuel filler cap. Information on this option will be found
in Section
9E.
FUEL TANK FILLER NECK
To help prevent refueling with leaded gasoline,
the fuel filler neck on gasoline engine cars has a built-in
restrictor and deflector. The opening in the restrictor
will only admit the smaller unleaded gas nozzle spout,
which must be fully inserted to bypass the deflector.
Attempted refueling with a leaded gas nozzle or failure

BATTERY 801-7
1 -BATTERY
2-CABLE ASM- NEG.
3-CABLE ASM- POS.
TO PREVENT DIODE DAMAGE, ALL CONNECTIONS MUST BE
MADE AND TIGHTENED BEFORE
BATTERY
POSlTVE CONNEC-
TION IS MADE.
Fig.
602 Battery Cables (LBS/LG4)
SPECIFICATIONS
ENGINE BATTERY/FUNCTION REPLACEMENT
LB8lL03 198 1730-STD 730
CCA 525
RC(MIN)90
~oad ~est 260 Amps
1981731-HD
CCA 570
RC(MIN)90
Load Test 280 AMPS
198 1W-STD
CCA 525
RC(MIN)75
Load Test 260 Amps
1981731-HD
CCA 570
RC(MIWW
Load Test 280 AMPS
1981601
CCA 630
RC(MIN)90
Load Test 310 AMPS

CRANKING SYSTEM BD2-9
I TESTING SERIES COIL FOR OPEN I
TESTING SOLENOID WINDINGS
c. Us~ng a test lamp. place onelead on the series coil ter-
minal and the other lead on the insulated brush. If the lamp
fails to light. the series coil is open and will require repair or
replacement. This test should be made from each insulated
brush to check brush and lead continuity.
TESTING SERIES COlL FOR GROUND
THESE TWO TERMINALS
MUST BE SEPARATED
d. On starters
withshunt coil. sepanate series and shunt
coil strap terminals during this test. Do not let strap terminals
touch case or other ground. Using a test lamp place one lead
on
he grounded brush holder and the other lead on either
insulated brush. If the lamp lights, a grounded series coil is
indicated and must be repaired or replaced. VOLTMETER
e. Check the current draw of the solenoid winding as fol-
lows:
If solenoid is not removed from starting motor. the connec-
tor
strap terminals must be removed from the terminal on the
solenoid before making these tests. Complete tests in a
minimum of time to prevent overheating of the solenoid.
To check hold-in winding, connect an ammeter in series
with 12-volt battery and the "switch" terminal on the solenoid.
Connect a voltmeter to the "switch" terminal and to ground.
Connect carbon pile across battery. Adjust the voltage to
10 volts and note the ammeter reading. It should be 13 to 19 amperes for all starting motors.
To check both windings. connect as for previous test.
Ground the solenoid motor terminal. Adjust the voltage to 10
volts and note the ammeter reading. It should be
59 to 79 am-
peres for all starting motors.
NOTE: Current will decrease as windings heat up.
Current draw readings that are over specifications indicate
shorted turns or a ground in the windings of the solenoid and the
solenoid should be replaced. Current draw readings that are
under specifications indicate excessive resistance. No reading
indicates an open circuit. Check connections then replace sole-
noid if necessary.
H20255.6D
Fig. 606 Starter Motor Disassembly, Test and Reassembly 4 of 6

684.4 IGNITION SYSTEM
a spark plug wire from a spark plug, twist the 4. Do not wipe grease from module, or distributor
boot on the spark plug and pull
on the boot to base,
if same module is to be replaced.
remove the wire, or use a special tool designed to
remove spark plug boots.
Install or Connect
Remove or Disconnect
1. Ignition switch battery feed wire and tachometer
lead (if equipped) from distributor cap. Also
release the coil connectors from the cap. (DO
NOT use a screwdriver or tool to release the
locking tabs.)
2. Distributor cap by turning four screws
counterclockwise. Move cap out of the way.
3. Four-terminal ECM harness from distributor.
4. If necessary, remove secondary wires from cap,
release wiring harness latches and remove wiring
harness retainer. The spark plug wire numbers
are indicated on the retainer.
5. Distributor clamp screw and hold-down clamp.
6. Note position of rotor, then pull distributor up
until rotor just stops turning counterclockwise
and again note position of rotor.
To insure correct timing of the distributor,
the distributor must be INSTALLED with
the rotor correctly positioned as noted.
If the engine was accidentally cranked after the
distributor was removed, the following procedure can
be used for installing:
1. Remove No. 1 spark plug.
2. Place finger over No. 1 spark plug hole and crank
engine slowly until compression is felt.
3. Align timing mark on pulley to "0" on engine
timing indicator.
4. Turn rotor to point between No. 1 and No. 8
spark plug towers on distributor cap on V8
engines, between No. 1 and No. 6 on V6 engines,
and No.
1 and No. 4 on 4 cylinder engines.
5. Install distributor and connect ignition feed wire.
6. Install distributor cap and spark plug wires.
7. Check engine timing (see Set Ignition Timing).
Install or Connect
1. Insert distributor, positioning rotor as removed.
2. Distributor hold-down clamp and screw.
3. Wiring harness retainer and secondary wires, if
removed.
4. ECM harness connector.
5. Distributor cap.
6. Coil connectors.
7. Battery wire and tachometer lead, if equipped.
Module
It is not necessary to remove the distributor from
car.
Remove or Disconnect
1. Distributor cap and rotor.
2. Two module attaching screws, and lift module
UP. 3. Leads from module. (Observe color code on leads
as these cannot be interchanged.)
NOTICE: If a new module is to be installed, a
package of silicone grease will be included with it.
Spread the grease on the metal face of the module
and on the distributor base where the module
seats. This grease is necessary for module cooling.
1. Module.
2. Module leads (observe color code).
3. Attaching screws to module.
4. Rotor.
5. Cap.
Pick-Up Coil
1. Remove distributor from car and follow
instructions in Unit Repair, as applicable.
Rotor
Fig. 1
1. Remove distributor cap.
2. The rotor is retained by two screws and is
provided with a slot which fits over a square lug,
,
so that the rotor can be installed in only one
position.
Integral Ignition Coil
Fig. I
Remove or Disconnect
1. Distributor cap.
2. Three coil cover attaching screws, and lift off
cover.
3. Coil attaching screws and lift ignition coil and
leads from cap.
Install or Connect I
1. Coil and attaching screws.
2. Coil leads.
3. Coil cover and attaching screws.
Capacitor
Fig. 1
The capacitor is part of the coil wire harness
assembly. Since the capacitor is used only for radio
noise suppression, it will seldom need replacement.
Remove or Disconnect I
1. Distributor cap and rotor.
2. Capacitor attaching screw and unplug connector
from module. It may help to loosen the module.
Install or Connect I
1. Plug into module.
2. Capacitor and hold-down screw (be sure ground
lead is under screw).

6E2-A-8 S.OL (VIN E) DRIVEABILITY AND EMISSIONS
DIAGNOSmIC CIRCUIT CHECK
The Diagnostic Circuit Check is an organized approach to identifying a problem created by an electronic
engine control system malfunction. It must be the starting point for any driveability complaint diagnosis,
because it directs the service technician to the next logical step in diagnosing the complaint.
The "Scan Data" listed in the table may be used for comparison, after completing the diagnostic circuit check
and finding the on-board diagnostics functioning properly and no trouble codes displayed. The "Typical Values"
are an average of display values recorded from normally operating vehicles and are intended to represent what a
normally functioning system would typically display.
A "SCAN" TOOL THAT DISPLAYS FAULTY DATA SHOULD NOT BE USED, AND THE PROBLEM
SHOULD BE REPORTED TO THE MANUFACTURER. THE USE OF A FAULTY "SCAN" CAN RESULT
IN MISDIAGNOSIS AND UNNECESSARY PARTS REPLACEMENT.
Only the parameters listed below are used in this manual for diagnosis. If
a "Scan" tool reads other
parameters, the values are not recommended by General Motors for use in diagnosis. For more description on the
values and use of the "Scan" to diagnosis ECM inputs, refer to the applicable diagnosis section in Section
"C". If
all values are within the range illustrated, refer to "Symptoms" in Section
"B".
""SCAN" DATA
Idle / Upper Radiator Hose Hot / Closed Throttle / Park or Neutral /Closed Loop / Acc. off
"SCAN" Position Units Displayed Typical
Data Value
Coolant Temp. CO 85" - 105"
TPS Volts .4 - 1.25
MAP Volts
1 - 2 (depends on Vac. & Baro pressure)
INT (Integrator) Counts Varies
BLM (Block Learn) Counts 118- 138
IAC Counts (steps) 1-50
RPM RPM 1000
k 75 RPM (depends on temperature)
0 2 Volts .001 - 999 and varies
OpenIClosed Loop OpenICIosed Closed Loop (may go open with extended idle)
A/C Request YesINo No (yes, with A/C requested)
PIN Switch PIN and RDL
ParkINeutral (PIN)
TCC
On/Off Off1 (on, with TCC commanded)
VSS MPH 0
Battery Volts 13.5- 14.5
Air Switch NormalIDivert Normal
Air Divert ConverterIPort Converter
Knock Signal
YesINo N o
4th Gear
YesINo No (Yes, if in 4th Gear)
MAT Temp.
CO 10" - 90" ( Depends on Under Hood Temp.).
Power Steering Pressure Switch
NormalIHi Pressure Normal

DRIVEABILITY AND EMISSIONS 5.OL (VIN E) 6EZ-C1-5
DIAGNOSIS
Since the ECM can have a failure which may
effect only one circuit, following the diagnostic
procedures in this section can reliably tell when a
failure has occurred in the ECM. Also,
a Code
55 in
dicates a failure of the ECM.
If a diagnostic chart indicates that the ECM
connections or ECM is the cause of a
problem,and the
ECM is replaced, but does not correct the problem, one
of the following may be the reason:
e
connections. - The diagnostic chart will say "ECM
Connections or ECM". The terminals mav have to be
removed from the connector in order to check them
properly.
@ The ECM or PROM is not correct for the
. - The incorrect ECM or PROM may cause
a malfunction and may or may not set a code.
. - This means that
time the system is
being checked. In this case, refer to the "Symptoms"
portion of the manual and make a careful physical
Solenoids and relays are turned "ON" and "OFF" by
the ECM, using internal electronic switches called
"Drivers".
A shorted solenoid, relay coil, or harness in a
GMP4 computer will not damage the ECM,
but will cause the circuit and controlled
component to be inoperative. When the
circuit fault is not present or has been
repaired, the "Quad-Driver" will again
operate in a normal manner due to it's fault
protected design. If a fault has been repaired
in a circuit controlled
by a "Quad-Driver", the
original
ECM should be reinstalled and the
circuit checked for proper operation.
ECM
replacement will not be necessary if the
repaired circuit or component now operates
correctly.
534636 or BT8405 testers or equivalent provide a
fast, accurate means of checking for a shorted coil or a
short to battery voltage.
e , - Although the
PROM rarely
fails,it operates as part of the ECM.
Therefore, it could be the cause of the problem.
Substitute a known good PROM.
o . - After the
ECM is replaced, the system should be rechecked for
proper operation. If the diagnostic chart again
indicates the ECM is the problem, substitute a known
good ECM. Although this is a rare condition, it could
happen. The
components or circuits and the codes or
charts, related to them are:
@ Code 55 indicates a failure of the ECM.
@ PROM - Code 51.
@ Coolant Temperature Sensor - CHARTS 14 -
15.
@ MAP sensor - CHART 33 or 34. To check the
sensor with no code set, use CHART
C-1D.
e TPS - CHARTS 21 or 22.
e PIN switch - CHART C-1A
@ Crank Signal - CHART C-1B
@ O2 Sensor - CHARTS 13,44,45.
@ VSS - CHART 24 and in TCC System.
e Distributor - CHART 42 and in EST system.
@ Distributor - Chart and in the EST system.
ECM
A faulty ECM will be determined in the diagnostic
charts, or by a Code 55.
PROM
An incorrect or faulty PROM, which is part of the
ECM, may set a Code 51.
ECM INPUTS
All of the sensors and input switches can be
diagnosed by the use of a "Scan" tool. Following is
a
short description of how the sensors and switches can
be diagnosed by the use of "a Scan" tool. The
"Scan"
tool can also by used to compare the values for a
normal running engine with the engine you're
diagnosing.
Coolant Temperature Sensor
A "Scan" tool displays engine temp. in degrees
centigrade. After the engine is started, the
temperature should rise steadily to about
90°C, then
stabilize when thermostat opens.
A fault in the
coolant sensor circuit should set a Code 14 or 15. The
code charts also contain a chart to check for sensor
resistance values relative to temperature.
MAT Sensor
A "Scan" tool displays temperature of the air
entering the engine and should read close ambient air
temperature, when engine is cold, and rise
as
underhood temperature increases. If the engine has
not been run for several hours (overnight), the MAT
sensor temperature and coolant temperature should
read close to each other.

DRIVEABILITY AND EMISSIONS 5.OL (VIN E) 6EZ-C1-7
BRACKET
INSTRUMENT PANEL
(INSTRUMENT PANEL) '
MODULE ASM ECM (TBI)
BRACKET
1 BOLTISCREW (5) - 1 NUT (4) 4.7-7.0 N.rn (3.3-5.1 LBS. FT.)
NUT
BOLTISCREW (2) 2.2-3.4 N,rn (1.6-2.5 LBS. FT.)
Figure C1-9 - ECM Mounting
NOTICE: To prevent internal ECM damage, the
ignition must be
"OFF" when
disconnecting or reconnecting power to
ECM (for example, battery cable, ECM
pigtail, ECM fuse, jumper cables,
etc.).
Remove or Disconnect
1. Negative battery cable.
2. Right hand hush panel.
3. Connectors to ECM.
4. ECM.
5. PROM from ECM.
Install or Connect
1. OldPROMinnewECM.
2. ECM into car.
3. Connectors.
4. Hush panel.
5. Negative battery cable.
PROM
Code 51 indicates a faulty PROM, bent pins, or
incorrect installation.
ECM HARNESS
PROM CARRIER CONNECTORS TO ECM
1 PROM ACCESS COVER 45 0463-6E
Figure C1-10 PROM Access Cover
1 PROM REMOVAL TOOL 45 0464-6E
Figure C1-I 1 PROM Removal Tool
Important
It is possible to install a PROM backward. If the
PROM is installed backward and the ignition key
turned to "ON," the PROM circuitry will bc
destroyed, requiring PROM replacement.
lmportant
The ignition should always be off wh~n installing
or removing the ECM connectors.
Remove or Disconnect
1. Connectors from ECM.
2. ECM mounting hardware.
3. ECM from passenger compartment.
4. Prom access cover (see Figure C 1- 10)
5, Remove PROM assembly

DRIVEABILITY AND EMISSIONS 5.OL (VIN E) 6EZ-C1-9
Figure C1-13 Removing Calpak
COOLANT SENSOR
NOTICE: Care must be taken when handling
coolant sensor. Damage to coolant sensor
will affect proper operation of the Fuel
Illjection system.
Remove or Disconnect
1. Negative battery cable.
2. Electrical connector.
3. Carefully back out coolant sensor.
lnstall or Connect
1. Sensor in engine.
2. Electrical connector.
3. Negative battery cable.
MAT Sensor
Remove or Disconnect
I. Negative battery cable.
2. Electrical connector.
3. Carefully back out sensor.
a Install or Connect
I. Coat threads only with sealant, PIN 1052080 or
equivalent.
2. Sensor in engine.
3. Electrical connector.
4, negative battery cable.
OXYGEN SENSOR
NOTICE:
The oxygen sensor uses a permanently
attached pigtail and connector. This
pigtail should not be removed from the
oxygen sensor. Damage or removal of the
pigtail or connector could affect proper
operation of the oxygen sensor.
rn Important
Take care when handling the oxygen sensor - - -
(Figure (21-14). The in-line electrical connector
and louvered end must be kept free of grease, dirt
or other contaminants. Also, avoid using cleaning
solvents of any tvpe.
Do not drop or roughly
handle the oxygen sensor.
a Remove or Disconnect
1 Negative battery cable.
2. Electrical connector.
3. Carefully back out oxygen sensor.
The oxygen sensor may be dit'ficult to remove
when engine temperature is below
48°C (120°F).
Excessive force may damage threads in exhaust
manifold or eshaust pipe.
1. Negative battery cable.
2. Electrical connector.
3. Carefully back out Oxygen Sensor.
lnstall or Connect
rn Important
A s~ecial anti-seize compound is used on the
oxygen sensor threads. The compound consists of
a liquid graphite and glass beads. The graphite
will tend to burn away, but the glass beads will
remain, making the sensor easier to remove.
New or service sensors will already have the
compound applied to the threads. If a sensor is
removed from an engine, and, if for any
reason it is
to be reinstalled, the threads must have
anti-sei~e
compound applied before reinstallation.
1. Coat threads of oxygen sensor with anti-seize
compound
PIN 3613695 or equivalent if neceshary.
2. Sensor, and torque to 41 N,M (30 ft. Ibs.).
3. Electrical connector.
4. Negative battery cable.
MAP SENSOR
Other than checking for loose hoses and electrical
connections the only service possible
is unit
replacement if diagnosis shows sensor to
be faulty.

6EZ-C2-4 DRIVEABILITY AND EMISSIONS - 5.OL (VIN El
[isj FUEL METER COVER bL BODY ASSEMBLIES
1 THROTTLE BODY ASSEMBLY
1 IDLE AIR CONTROL VALVE ASSEMBLY - FILTERED AIR INLET
PlNTLE
TWRO$TLE VAWE
VACUUM PORTS - FOR ENGINE OR EMISSION
CONTROLS
8P 0319-SY 111 5W7
Figure C2-5 - ldle Air Contol System
ldle Air Control (IAC) Valve
The purpose of the idle air control (IAC) valve , is
to control engine idle speed, and prevent stalls due to
changes in engine load (see Figure
C2-5) .
The IAC valve, mounted on the throttle body,
controls bypass air around the throttle valve By
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 valve. If rpm is too low,
more air is bypassed around the throttle valve to
increase rpm.
11 rpnl is too high, less air is bypassed
around the
throt:le valve to decrease rpm.
The IAC valve moves in small steps called
"Counts," and can be monitored by
a "Scan" tool which
plugs into the assembly line data
link (ALDI,)
connector
During idle, the proper position of the IAC valve is
calculated by the ECM based on battery voltage,
coolant temperature,
ellgine load, and engine rpm. If
the rpm drops below a specified rpm, and the throttle
valve is closed, the ECM senses a near stall condition.
The ECM will then calculate a new IAC valve position
to prevent stalls.
If the IAC valve is disconnected or connected with
the engine running, the idle
rpnl may he wrong. In
this case, the
IAC valve may he reset by turning the
ignition switch "ON" and
"OFF" one time
'I'he IAC valve affects only the idle characteristics
of the engine
If it i.; ol)cltl fullv, too much ,LII. tc 111 I)(>
BALL BEARING ASSEMBLY -
STATOR ASSEMBLY
ROTOR
ASSEMBL
I
SPRING
PlNTLE
LEAD SCREW A
Figure C2-6 - ldle Air Control (IAC) Valve
allowed to the manifold and idle speed will he high. if
it is stuck closed, too little air will be
allo\verl 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.
On
4.3L (VIN Z) V6, LB4 engines, for "B" and "G"
cars, the valve is thread mounted, with a dual taper,lO
mm diameter pintle (Figure C2-6). If replacement is
necessary, use only an IAC valve with the correct part
number and appropriate pintle shape and diameter.
I THROTTLE VALVE
ENGINE CONTROL MODULE (ECM)
,q
THROTTLE POSITION
SENSOR (TPS)
Figure C2-7 - Throttle Position Sensor
Throttle Position Sensor (TPS)
The throttle position sensor ('I'PS), is mounted on
the side of the throttle body opposite the throttle lever
assembly. Its function is to sense the current throttle
valve position
and relkly that information to the ECM
(Figure (22-7). Knowledge of throttle position allows
lhe ECM to generate the recluired i~jector control
signals (base pulse). If the 'I'PS senses a wide open
throttle,
a voltc\ge sic,ll,~I il~tlic~ttinq this condition 13

DRIVEABILITY AND EMISSIONS - 5.OL (\/IN El 6EZ-CZ-5
sent to the ECM. The ECM then increases the injector
base pulse width, permitting increased fuel flow.
As the throttle valve rotates in response to
movement of the accelerator pedal, the throttle shaft
transfers this rotational movement to the
'I'PS. A
potentiometer (variable resistor) within the TPS
assembly changes its resistance (and voltage drop) in
proportion to throttle movement.
By applying a reference voltage (5.0 volts) to the
TPS input, a varying voltage (reflecting throttle
position) is available at the TPS output. For example,
approximately 2.5 volts results from a 50% throttle
valve opening (depending on TPS calibration). The
voltage output from the TPS assembly is routed to the
ECM for use in determining throttle position.
FUEL PUMP
The fuel pump is a turbine type, low pressure
electric pump, mounted in the fuel tank. Fuel
is
pumped at a positive pressure (above 62
kPa or 9 psi)
from the fuel pump through the in-line filter to the
pressure regulator in the TBI assembly Excess
fuel is
returned to the fuel tank through the fuel return line.
The fuel pump is attached to the fuel gage sender
assembly. A fuel strainer is attached to the fuel pump
inlet line and prevents dirt particles from entering the
fuel line and tends to separate
water from the fuel
Vapor lock problems are reduced when using an
electric
pump because the fuel is pushed from the tank
under pressure rather than being pulled
under
vacuum, a condition that produces vapor.
An inoperative fuel pump would cause
a. no start
condition. A fuel pump which does not provide enough
pressure can result in poor performance. (See "Fuel
System Pressure Test" procedure).
FUEL PUMP ELECTRICAL CIRCUIT
When the key is first turned "ON" without the
engine running, the ECM turns 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 shuts the fuel pump "OFF" and
waits until the engine starts. As soon as the engine is
cranked, the ECM turns the relay
"ON" and runs 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 sender has two circuits
internally. One operates the oil pressure indicator or
gage in the instrument cluster,
itnd the other is
anormally open switch which closes when oil pressure
reaches about 28
kPa (4 psi). If the fuel pump relay
fails, the oil pressure switch will run the fuel pump. An
inoperative fuel pump relay can result in long
cranking times, particularly if the engine is cold. The
oil pressure switch will turn on the fuel pump as soon
as oil pressure
reaches about 28 kPa (4 psi).
FUEL CONTROL
Always start with the "Diagnostic Circuit Check"
in Section
"6E2-A". This will reduce diagnosis time
and prevents unnecessary replacement of parts. The
information in this check will direct diagnosis
concerning "Engine
Crunlis But Won't Run" and the
"Fuel Control System," Section
"6E2-C2", including
diagnosis of an injector, pressure regulator,
fuel pump,
fuel
pump relay, and oil pressure switch.
Idle Air Control (IAC) Valve
A "Scan" tool reads IAC position in steps, calletl
"Counts." "0" steps indicates the ECM is commanding
the
IAC to be driven in, to a fully seiltetl position
(minimum idle air).
The higher the number steps, the
more idle air being allowed to pass
by the IAC valve.
cnose Refer to CHART C-2C for information to cliil,
the function of the IAC valve.
Driva bility
Refer to Section "B" for driveability symptoms
related to the fuel control.
ON-VEHICLE SERVICE
GENERAL SEWVICE INFORMATION
CAUTION:
e To prevent personal injury or damage to the
vehicle
as the result sf an accidental start,
disconnect and reconnect the negative
battery cable before and after service is
performed.
@ Also, catch any fuel that leaks out when
disconnecting the fuel lines, by covering the
fittings with
a shop cloth. Place the cloth in
an approved container when work is
complete.
The 'FBI unit repair procedures cover component
replacement with the unit on the vehicle,
tIowever,
throttle body replacement requires that the complete
unit
be removed from the enginc.