1988 PONTIAC FIERO diagram

6E3-A-36 5.OL (VIN F) & 5.7L (VIN 8) DRIVEABILITY AND EMISSIONS
CONNECTOR
15- WAY .I.P. CONNECTOR - - PARK OR NEUTRAL
CODE 24
VEHICLE SPEED SENSOR (VSS) CIRCUIT
5.0L (VIN F) & S.SL (VIN 8) "F" SERIES (PORT)
rcuit Description:
'I'he ECM applies and monitors 12 volts on CKT 437. CK'I' 437 connects to the vehicle speed sensor buffer
which alternately grounds CKT 437 when drive wheels are turning. This pulsing action takes place about 2000
times per mile and the ECM will calculate vehicle speed based on the time between "pulses".
A "SCAN" tool reading should closely match with speedometer reading with drive wheels turning.
Test Description: Numbers below refer to circled
numbers on the diagnostic chart.
1. Code
24 will set it
@ CKT 437 voltage is constant.
@ Engine speed between 1400 and 3600 rpm.
@ Less than 2% throttle opening, about .10V
( 100mV) above close throttle.
@ Low load condition (low air flow).
@ Not in park or neutral.
@ All conditions must be met for 4 seconds.
'I'hese conditions are met during a road load
deceleration.
2. A voltage of less than 1 volt at the 15-way
connector indicates that the CKT 437 wire may be
shorted to ground. Disconnect CKT 437 at the VSS
buffer. If voltage now reads above 10 volts, the
VSS buffer is faulty. If voltage remains less than
10 volt, then CKT 437 wire is grounded
or open. If
437 is not grounded or open, check for a faulty
ECM connector or ECM.
Diagnostic Aids:
If "Scan" displays vehicle speed, check
parWneutra1 switch CHART C-1A on vehicle with
auto trans. If switch is
OK check for intermittent
connections. An open or short to ground in CKT 437
will result in a Code 24
If the customer also
complained about a loss of mph on the
I.P., check the
P.M. generator circuit. Refer to Section "8A" for
complete wiring diagram.
Refer to "Intermittents" in Section
"B".

6E3-B-2 5.OL (VIN F) & 5.7L (VIN 8) DRIVEABILITY AND EMISSIONS
Problem may or may not turn "ON" the "Service Engine Soon" light, or store a code.
DO NOT use the Trouble Code Charts in
An intermittent "Service Engine Soon" light
Section A for intermittent problems. The fault must
with no stored code may be caused by:
be present to locate the problem. If a fault is
@ Ignition coil shorted to ground and arcing at
intermittent, use of Trouble Code Charts
may result
spark plug wires or plugs.
in replacement of good parts.
"Service Engine Soon" light wire to
ECM
@ Most intermittent problems are caused by
shorted to ground. (CKT 419).
faulty electrical connections or wiring. Perform
Diagnostic "Test" Terminal wire to ECM,
careful check as described at start of Section
shorted to
ground.(CKT 451)
"B". Check for:
@ ECM power grounds. See ECSI wiring
@ Poor mating of the connector halves, or diagrams.
terminals not fully seated in the connector
@ Loss of trouble code memory. To check,
body (backed out). disconnect TPS and idle engine until "Service
@ Improperly formed or damaged terminals.
Engine Soon" light comes on. Code 22 should be
All connector terminals in problem circuit
stored, and kept in memory when ignition is
should be carefully reformed or replaced to turned "OFF". If not, the ECM is faulty.
insure proper contact tension.
@ Check for an electrical system interference
@ Poor terminal to wire connection. This caused by a defective relay, ECM driven
requires removing the terminal from the
solenoid, or switch. They can cause a sharp
connector body to check. See "Introduction"
electrical surge. Normally, the problem will
to Section
"6E". occur when the faulty component is operated.
@ If a visual check does not find the cause of the @ Check for improper installation of electrical
problem, the car can be driven with a voltmeter
options, such as lights,
%way radios, etc.
connected to
a suspected circuit. A "Scan" tool
EST wires should be kept away from spark plug
can also be used for monitoring input signals to wires, distributor wires, distributor housing,
the ECM to help detect intermittent conditions. coil, and generator. Wire from
ECM to
An abnormal voltage, or "Scan" reading, when distributor
(CKT 453) should be a good
the problem occurs, indicates the problem
may connection.
be in that circuit. If the wiring and connectors
@ Check for open diode across AIC compressor
check OK and a Trouble Code was stored for a
clutch, and for other open diodes (see wiring
circuit having a sensor, except for Codes
43, 44, diagrams).
and 45, substitute a known good sensor and
recheck.
HARD START
Definition: Engine cranks OK, but does not start for a long
time. Does eventually run, or may start but immediately dies.
Perform careful check as described at start of
Section
"B".
@ Make sure driver is using correct starting
procedure.
@ CHECK:
- TPS for sticking or binding or a high TPS
voltage with the throttle closed (should read
less than
.700 volts).
- High resistance in coolant sensor circuit or
sensor itself. See Code 15 chart or with
a
"Scan" tool compare coolant temperature with
ambient temperature on a cold engine.
- Fuel pressure CHART A-7.
- Water contaminated fuel.
- EGR operation. Be sure valve seats properly and
is not staying open. See CHART C-7.
- Both injector fuses (visually inspect).
- Ignition system - Check distributor for:
Proper Output with ST-125.
Worn shaft.
Bare and shorted wires.
Pickup coil resistance and connections.
Loose ignition coil ground.
Moisture in distributor cap.
@ If problem exists in cold weather, check cold start
valve. See CHART A-9.

6E3-B-4 5.OL (VIN F) & 5.7L (VIN 8) DRIVEABILITY AND EMISSIONS
LACK OF POWER, SLUGGISH, OR SPONGY
Definition: Engine delivers less than expected power. Little or
no increase in speed when accelerator pedal is pushed down part way.
@ Perform careful visual check as described at
start of Section "B".
@ Compare customer's car to similar unit.
Make sure the customer's car has an actual
problem.
@ Remove air cleaner and check air filter for
dirt, or for being plugged. Replace as
necessary.
@ CHECK:
- For loose or leaking air duct between MAF
sensor and throttle body.
- Ignition timing. See emission control
information label.
- Restricted fuel filter, contaminated fuel or
improper fuel pressure. See CHART A-7.
- ECM Ground circuits - See ECM wiring
diagrams.
- EGR operation for being open, or partly open
all the time
- CHART C-7.
- Exhaust system for possible restriction: See
CHART
B-1.
- Inspect exhaust system for damaged or
collapsed pipes.
- Inspect muffler for heat distress or possible
internal failure.
- For possible plugged catalytic convertor by
comparing exhaust system backpressure on
each side at engine. Check backpressure by
removing
A.1.R check valves near exhaust
manifolds. See CHART
B-1 for procedure.
- Generator output voltage. Repair if less than 9
or more than 16 volts.
- Engine valve timing and compression.
- Engine for proper or worn camshaft. See Section
"6A".
- Secondary voltage using a shop ocilliscope or a
spark tester
5-26792 (ST-125) or equivalent.
- Check for excessive knock retard. See CHART
C-5.
DETONATION ISPARK KNOCK
Definition: A mild to severe ping, usually worse under
acceleration. The engine makes sharp metallic knocks that
change with throttle opening. Sounds like popcorn popping.
@ Check for obvious overheating problems:
- Low coolant.
- Loose water pump belt.
- Restricted air flow to radiator, or restricted
water flow thru radiator.
- Inoperative electric cooling fan circuit. See
CHART C-12.
@ CHECK:
- Ignition timing. See vehicle emission control
information label.
- EGR system for not opening - CHART C-7.
- TCC operation - CHART C-8.
- Fuel system pressure. See CHART A-7.
- Mem-Cal - Be sure it's the correct one. (See
"Service Bulletins").
- Valve oil seals for leaking.
@ Check for incorrect basic engine parts such as
cam, heads, pistons, etc.
@ Checkforpoorfuelquality.
@ Remove carbon with top engine cleaner. Follow
instructions on can.
@ Check ESC system
See CHART C-5
@ To help determine if the condition is caused by a
rich or lean system, the car should be driven at
the speed of the complaint. Monitoring block
learn at the complaint speed will help identify the
cause of the
problem. If the system is runnig lean
(block learn greater than
1381, refer to
"Diagnostic Aids" on facing page of Code
44. If
the system is running rich (block learn less than
1181, refer to "Diagnostic Aids" on facing page of
Code 45.

6E3-C-1 5.OL (VIN F) & 5.7L (VIN 8) DRIVEABILITY AND EMISSIONS
COMPONENT SYSTEMS
Section "C" provides information on the following:
@ General description of components and systems .
@ On-vehicle service .
@ Part names and group numbers .
@ Diagnostic charts . These include a functional check of the system as well as diagnosis of any problem
found in the functional check
.
For locations of components, wiring diagrams, and ECM Terminal End View. refer to the front on the "A"
section of the engine being diagnosed
.
Following are the sub-section identification and the system covered:
............................. @ C1 Electronic Control Module (ECM) and Sensors Page C1-I
@ C2 Fuel Control System ................................................. Page C2-I
.............................. @ C3 Evaporative Emission Control System (EECS) Page C3-1
@ C4 Ignition SystemIEST ................................................ Page C4-1
@ C5 Electronic Spark Control ............................................. Page C5-1
..................................... @ C6 Air Injection Reaction (AIR) System Page C6-1
.................................. @ C7 Exhaust Gas Recirculation (EGR) System Page C7-1
.................................... C8 Transmission Converter Clutch (TCC) Page C8-1
................................................. @ C12 Electric Cooling Fan Page C12-1
................................... @ C13 Positive Crankcase Ventilation (PCV) Page C13-1
DIAGNOSTIC CHARTS
The Diagnostic Charts for each system are found after the on-car service and parts information at the back of
each section
. Following are the charts found in this section .
@ Chart C-1A Park Neutral Switch ........................................... Page C1-10
@ Chart C-2A Injector Balance Test .......................................... Page C2-18
@ Chart C-2C Idle Air Control (IAC) System Check ............................... Page C2-20
@ Chart C-3 Canister Purge Valve Check ..................................... Page C3-4
@ Chart C-4 Ignition System Check ......................................... Page C4-4
@ Chart C-5 Electronic Spark Control System Check ............................ Page C5-4
@ Chart C-6 AIR Management Check ....................................... Page C6-6
@ Chart C-7 Exhaust Gas Recirculation (EGR) Check ............................. Page C7-4
@ Chart C-8A Automatic
Transmission Converter Clutch (TCC) ...................... Page C8-6
......................... @ Chart C-8B Manual Transmission Shift Light Diagnosis Page C8-10
@ Chart C-12 Cooling Fan Control Circuit Diagnosis ............................. Page C12-2

INDEX
SECTION PAGE
Cooling Fan Control
................. General Description C12-1
........................ Diagnosis C12-2
........................... Cuts Out B-5
................... Cylinder Select Error A-48
.................... Deceleration Mode C2-3
......................... Detonation B-4
..................... Dieseling. Run On B-6
............. Distributor Reference Signal C1-4
...................... ECM Terminals A-7
.................. ECM Wiring Diagram A3-A6
EGR Control Valve
................. General Description C7-1
................. Valve Identification C7-2
................... Diagnosis. Service C7-2
A-40
.................. EGR Control Solenoid C7-3
......................... EGR Check C7-4
Electronic Control Module
................. General Description C1-1
......................... Diagnosis C1-4
............................ Service C1-5
..................... Function Check C1-7
Electronic Spark Control (ESC) System
................. General Description C5-1
................... Diagnosis. Service C5-4
Electronic Spark Timing EST
............. A-50
A-52
Engine Cranks But Won't Run
............ A-14
........................ Engine Knock C5-4
.......................... ESC Module C5-2
.......................... ESC Sensor C5-1
.................... ESC System Check C5-4
................... ESTllgnition System C4-1
Evaporative Emission Control System
................. General Description C3-1
.......................... Diagnosis C3-2
Exhaust Emissions Excessive (Odors)
....... B-7
Exhaust Gas Recirculation (EGR) System
.... C7-1
Exhaust System Check Restricted
......... B-8
Fuel Control System
................. General Description C2- 1
......................... Diagnosis C2-5
..................... Fuel Cutoff Mode C2-3
SECTION PAGE
Fuel Injectors ........................
Fuel Pressure Connection Assy ............
Fuel Pressure Relief Procedure ...........
Fuel Pump Electrical Circuit .............
Fuel Pump Relay ......................
Fuel Rail
General Description
.................
........................... Service
Fuel System Diagnosis
..................
Fuel System Pressure Test ...............
Fuel Tank Pressure Control Valve .........
.......................... Hard Start B-2
.......... HE1 High Energy Ignition System C4-1
.......................... Hesitation
B-3
............ Idle Air Control System Check C2-20
.................. Idle Air
Control Valve C2-4
......................... Diagnosis C2-5
.................... Ignition System EST C4-1
........ Ignition System Check Integral Coil C4-4
........................ Incorrect Idle B-6
.................. Information Sensors C1.2. 9
.................. Injector
Balance Test C2-18
........................ lntermittents B-2
........................ Knock Sensor C1-3
........................ Lack Of Power B-4
......... Light. Manual Transmission Shift C8-6
.............. Light. Service Engine Soon A-10
MAF Sensor
.................. General Description C1-2
.......................... Diagnosis C1-5
A.42.44. 46
............................ Service C1-8
... Manual Transmission Electrical Diagnosis C8-10
MAT Sensor
.................. General Description C1-2
......................... Diagnosis C1-5
A.34. 38

INDEX
SECTION
PAGE
MEM -Cal
General Description ................. C1-I
Diagnosis ......................... C1-4
A-60
Service
........................... C1-6
Functional Check
................... C1-7
Minimum
Idle Speed Adjustment ......... C2-12
Misses ............................. 8-5
Negative Backpressure Valve ............ C7-2
No ALDL Data
....................... A- 12
No "Service Engine Soon" Light
.......... A-10
.................... Oil Pressure Switch C2-16
Oxygen Sensor
General Description
.................. C1-3
......................... Diagnosis C1-5
A.24.54. 56
........................... Service C1-8
Park Neutral Switch
General Description
................. C1-3
Diagnosis
.......................... C1-10
C1-5
Service
........................... C1-9
Poor Fuel Economy
.................... B.6.
C5-4
Poor Performance
.................... C5-4
Positive Crankcase Ventilation (PCV)
General Description. Diagnosis
......... C13-1
Service
............................ C13-2
Pressure Regulator
.................... C2-4
........................ Quad Drivers C 1-4
..................... Reference Signal C1-5
.......................... Rough Idle B-6
RunMode .......................... C2-2
RunOn ............................. B-6
SECTION PAGE
................... Sensor Information C1-2-9
"Service Engine Soon" Light On Steady .... A- 12
................... Setting Timing ... . C4-2
.......................... Shift Light C8-6
Sluggish
............................ B-4
......................... Spark Knock B-4
........................ Speed Sensor C8-2
.................. Speedo Buffer Sensor C8-4
Spongy
............................. B-4
............................ Stalling B-6
........................ Starting Mode C2-2
........................... Stumble B-3
Surges
............................. B-3
.................. System Over Voltage A-60
Throttle Body Unit
................. General Description C2-3
........................... Service C2-11
Throttle Position Sensor
................. General Description C1-3
......................... Diagnosis C1-5
A-30
....................... Adjustments C2-12
........................... Service C1-8
Transmission Converter Clutch TCC System
.................. General Description C8-1
......................... Diagnosis C8.2. 4
U
........................ Unstable Idle B-6
V
...................... Vapor Canister C3-1
Vehicle Speed Sensor
.................. General Description C1-3
.......................... Diagnosis C1-5
A-36
Vehicle Anti-Theft System (VATS)
................. General Description A-58
......................... Diagnosis A-59
W
...................... Wiring Diagrams A-3
................... Won't Flash Code 12 A-
12
Sag
.................+............. B-3
......................... "Scan" Data A-8

DRIVEABILITY AND EMISSIONS - FUEL INJECTION 6E-3
VEHICLE EMISSION CONTROL INFORMATION
MBEL
The Vehicle Emission Control Information label
(Figure
1) contains important emission specifications
and setting procedures. In the upper left corner is
exhaust emission information which identifies the
year, the manufacturing division of the engine, the
displacement in liters of the engine, the class of
vehicle and type of fuel metering. Also there is an
illustrated emission component and vacuum hose
schematic. A similar label is located in the engine
compartment of every General Motors Corporation
vehicle. If the label has been removed, it can be
ordered from the parts division.
(WDDGM)
INTRODUCTION
Electronic Engine Control
Each engine has an electronic engine control
module
(ECM) to control the fuel system. The ECM
varies the
airlfuel ratio by controlling the fuel flow
through the
injectorb).
In addition, the ECM controls the ignition timing
as well as the fuel pump and other systems.
It is important to review the component sections
and wiring diagrams in Section
"6E2" and "6E3" for a
specific engine, to determine what is controlled by the
ECM and what systems are
non-ECM controlled.
What This Section Contains
Each General Motors engine has system controls
to reduce exhaust emissions while maintaining good
driveability and fuel economy. This section explains:
@ Wow to use the Driveability and Emission
Sections
"6E2" for TBI, and "6E3" for Port
Fuel engines.
A brief description of systems used to control
fuel and emissions.
@ Abbreviations that are used in "Driveability
and Emissions".
@ Wiring harness service information for
harnesses used with the ECM.
@ Special tools used to diagnosis and repair a
system. Before
checking the system, observe the following:
Blocking Drive Wheels
The vehicle drive wheels always should be
blocked, and parking brake firmly set, while checking
the system.
Cold Oxygen Sensor
On some engines, the oxygen sensor will cool off
after only a short period of operation at idle. This will
put the system into "Open Loop". To restore "Closed
Loop" operation, run the engine at part throttle and
accelerate from idle to part throttle a few times until
the system goes "Closed Loop".
VlSUAUPHYSlCAL UNDERHOOD
INSPE6"rON
This can often lead to fixing a problem without further
steps. Inspect all vacuum hoses for correct routing,
pinches, cuts, or disconnects. Be sure to inspect hoses
that are difficult to see beneath the air cleaner,
compressor, generator, etc. Inspect all the wires in the
engine compartment for correct and good connections,
burned or chafed spots, pinched wires, or contact with
sharp edges or hot exhaust manifolds. This
visual/physical inspection is very important. It must ,
be done carefully and thoroughly.
BASIC KNOWLEDGE REQUIRED
Before using this section of the service manual,
there are some areas that you should be familiar with.
Without this basic knowledge, you will have trouble
using the diagnostic procedures contained in this
section.
Basic Electric Circuits
You should understand the basic theory of
electricity, and know the meaning of voltage, amps,
ALL NEW GENERAL MOTORS VEHICLES ARE CERTIFIED BY THE UNITED STATES
ENVIRONMENTAL PROTECTION
AGENCY AS CONFORMING TO THE REQUIREMENTS OF THE
REGULATIONS
FOR THE CONTROL OF AIR POLLUTION FROM NEW MOTOR VEHICLES. THlS
CERTIFICATION IS CONTINGENT OM CERTAIN ADJUSTMENTS BEING SET TO FACTORY
STANDARDS. IN MOST CASES, THESE ADJUSTMENT
POINTS EITHER HAVE BEEN
PERMANENTLY SEALED
AND/OR MADE INACCESSIBLE TO PREVENT INDISCRIMINATE OR
ROUTINE ADJUSTMENT IN THE FIELD. FOR
THlS REASON, "TI- FACTORY PROCEDURE FOR
TEMPORARILY REMOVING PLUGS, CAPS, ETC., FOR PURPOSES OF SERVICING THE PRODUCT,
MUST BE STRICTLY FOLLOWED AND, WHEREVER PRACTICABLE, RETURNED
TO WE
ORIGINAL INTENWF THE DESIGN.

6E-4 DRIVEABILITY AND EMISSIONS - FUEL INJECnON
and ohms. You should understand what happens in a
circuit with an open or a shorted wire. You should be
able to read and understand a wiring diagram. A
short to ground
is referred to as a ground to
distinguish it from a short between wires.
Use of Circuit Testing Tools
You should know how to use a test light, how to
connect and use
a tachometer, and how to use jumper
wires to by-pass components to test circuits. Care
should be taken to not deform the terminal when
testing.
Use of Digital Volt-Ohm Meter (DVM)
You should be familiar with the digital volt-ohm
Meter, particularly essential tool J-29125-A,
J34029A
or equivalent. You should be able to measure voltage,
resistance, and current, and know how to use the
meter correctly.
The digital volt-ohm meter is covered in the
"Special
ToolsJ'portion of this section.
DIAGNOSTIC INFORMATION
The electronic control module (ECM) is equipped
with a self-diagnosis system which detects system
failure and aids the technician by identifying the
circuit at fault via a trouble code. Below is
information about the way the ECM displays a
problem and how this corresponds to a trouble code in
the ECM. The ECM can also indicate an "Open Loop"
or "Closed Loop" mode.
"'Service Engine Soonw Light
This light is on the instrument panel, and has two
functions:
@ It is used to tell the driver that a problem has
occurred, and that the vehicle should be taken for
service as soon as reasonably possible.
@ It is used by the technician to read out "Trouble
CodesJ' to help diagnose system problems.
As a bulb and system check, the light will come
"ON" with the key "ON" and the engine not running.
When the engine is started, the light will turn "OFF".
If the light remains "ONJ', the self-diagnostic system
has detected a problem. If the problem goes away, the
light will go out in most cases after 10 seconds, but a
Trouble Code will remain stored in the ECM.
Intermittent "Service Engine Soon" Light
The diagnostic charts in Section "A" are set up to
check whether or not a stored trouble code is
"intermittent" or "hard". An
"intermittent" code is one which does not
always reset when the code setting parameters are
met, or is not present while you are working on the
vehicle. This is often caused by
a loose connection.
The facing page will contain diagnostic aids to help in
detecting
intermittents.
A "hard" code is one which is present when you
are working on the vehicle and the condition still
exists while working on the vehicle. The chart with
the stored trouble code number will lead you to the
cause of the problem.
Trouble Codes
The engine control module (ECM) is really a
computer. It uses sensors to look at many engine
operating conditions. It has
a memory and it knows
what certain sensor readings should be under certain
conditions. These conditions are described on the
facing page of each Trouble Code chart. If a sensor
reading is not what the ECM thinks it should be, the
ECM will turn "ON" the "Service Engine Soon" light
on the instrument panel, and will store a Trouble Code
in the memory. The Trouble Code tells which circuit
the trouble is in. A circuit consists of a sensor (such as
coolant temperature), the wiring and connectors to it,
and the ECM.
i
To get a Trouble Code out of the ECM, we use the
assembly line diagnostic link (ALDL) connector.
!
ALDL Connector I
I
The assembly line diagnostic link (ALDL) is a
diagnostic connector located in the passenger
compartment (Figure 2). It has terminals which are
used in the assembly plant to check that the engine is
operating properly before it leaves the plant.
Terminal "B" is the Diagnostic terminal, and it can be
connected to terminal
"A", or ground, to enter the
Diagnostic mode, or the Field Service Mode.
The ALDL connector is also used by "ScanJ' tools to
read information from the ECM via the Serial Data
Line. Serial Data information
is used extensively
throughout the manual.
Diagnostic Mode
1
If the Diagnostic terminal is grounded with the
ignition "ON" and the engine stopped, the system will
enter the Diagnostic Mode. In this mode the ECM
will:
1. Display a Code 12 by flashing the "Service Engine
Soon" light (indicating the system is operating). A
Code 12 consists of one flash, followed by a short
pause, then two flashes in quick succession. This
code will be flashed three times. If no other codes