1988 PONTIAC FIERO Service Repair Manual

6E3-B-8 5.OL (VIN F) & 5.7L (VIN 8) DRIVEABILITY AND EMISSIONS
RESTRICTED EXHAUST SYSTEM CHECK
ALL ENGINES
Proper diagnosis for a restricted exhaust system is essential before any components are replaced. Either
of
the following procedures may be used for diagnosis, depending upon engine or tool used:
CHECK AT A. I. R. PIPE: - OR CHECK AT 02 SENSOR:
1. Remove the rubber hose at the exhaust I. Carefully remove O2 sensor.
manifold
A.I.R. pipe check valve. Remove 2. Install Borroughs Exhaust Rackpressure
check valve.
'Pester (BT 8515 or BT 8603) or equivalent in
2. Connect
a fuel
punip pressure gauge to a hose place
of O2 sensor (see illustration).
and nipple from
a Propane Enrichment 3
After completing test described below, be
Device
(526911) (see illustration). sure
to coat threads of O2 sensor with anti-
3. Insert the
nipple into the exhaust manifold seize compound PIN 5613695
or equivalent
prior to re-installation.
HOSE AND NIPPLE ADAPTER
EXHAUST MANIFOLD
A.I.R. PIPE (EXHAUST PORT)
OXYGEN
(0,) SENSOR
1. With the engine idling at normal operating temperature, observe the exhaust system backpressure
reading on the gauge. Reading
should not exceed 1 + psi (8.6 kPa).
2. Accelerate engine to 2000 RPM and observe gauge. Reading should not exceed 3 psi (20.7 kPa).
3. If
the backpressure, at either RPM, exceeds specification, a restricted exhaust system is indicated.
4. Inspect the entire exhaust system for a collapsed pipe, heat distress, or possible internal muffler failure.
5. If there are no obvious reasons for the excessive hackpressure, a restricted catalytic converter should be
suspected and replaced using current
recommended procedures.

DRIVEABILITY AND EMISSIONS 5.OL (VIN F) & 5.7L (VIN 8) 6E3-B-9
BLANK

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

DRIVEABILITY AND EMISSIONS 5.0L (VIN F) & 5.7L (VIN 8) 6E3-C1-1
SECTION C1
ELECTRONlC CONTROL MODULE (ECM) AND SENSORS
CONTENTS
GENERAL DESCRIPTION ................ C1-I
ELECTRONIC CONTROL MODULE ....... C1-I
PJIEM-CAL......................... C1-I
ECM Function.. .................. C1-I
INFORMATION SENSORS ............. Cl-2
Engine Coolant Temperature Sensor . . C1-2
MAF Sensor ..................... C1-2
MAT Sensor .................... C1-2
Oxygen (02) Sensor. ............... C1-3
Throttle Position Sensor ............ C1-3
Knocksensor .................... C1-3
Vehicle Speed Sensor .............. C1-3
...... ParkINeutral Switch (Auto Only) C1-3
NC "ON" Signal .................. C1-4
Distributor Reference Signal ......... C1-4
DIAGNOSIS
......................... C1-4
ECM............................. C1-4
MEM-CAL......................... C1-4
ECMINPUTS....................... C1-4
........ Coolant Temperature Sensor C1-5
GENERAL DESCRIPTION
ELECTRONIC CONTROL MODULE (ECM)
The electronic control [nodule (ECM) (Figure C1-
11, located under the instrument panel, is the control
center of the fuel injection system. It constantly looks
at the information from various sensors,
and controls
the systems that affect vehicle performance. The
ECM performs the diagnostic function of the system.
-- Figure C1-1 - Electronic Control Module (ECM)
MAF Sensor ..................... C1-5
MAT Sensor ..................... C1-5
Oxygen (02) Sensor ............... C1-5
TPS ........................... C1-5
VSS ........................... C1-5
PIN Switch ...................... C1-5
NC Request Signal ................ C1-5
Reference Signal ................. C1-5
ON-CAR SERVICE
..................... C1-5
ELECTRONIC CONTROL MODULE ....... C1-5
ECM or MEM-CAL REPLACEMENT ....... C1-6
Funct~onal Check ................. C1-7
COOLANT SENSOR .................. C1-7
MAFSENSOR ...................... C1-8
MAF SENSOR POWER & BURN-OFF RELAY . C1-8
OXYGEN SENSOR .................. C1-8
THROTTLE POSITION SENSOR ......... C1-8
PARKINEUTRAL SWITCH ............. C1-9
PARTS INFORMATION
................. C1-9
It can recognize operational problems, alert the driver
through the "Service Engine Soon" light, and store a
code or codes which identify the problem areas to aid
the technician in making repairs. See Section
"6E"
for more information on using the diagnostic function
of the
ECM.
For service, this ECM only consists of two parts: a
controller (the ECM without a
Mem-Cal) and an
assembly called a Mem-Cal. (This stands for "Memory
and Calibration" Unit).
M EM-CAL
This assembly contains both thc functions of thc
PROM and CalPak. Like the PROM, it contains the
calibrations needed for a specific vehicle as well as the
back-up fuel control circuitry required if the rest of the
ECM becomes damaged or faulty.
ECM Function
The ECM supplies either 5 or 12 volts to power
various sensors or switches.
This is done through
resistances in the ECM which are so high in value
that a test light will not light when connected to the
circuit.
In some cases, even an ordinary shop
voltmeter will not give an accurate reading because
its resistance is too low. Therefore, a
10 nleg ohm
input impedance digital voltmeter is
requircd to
assure accurate voltage readings.

6E3-61-2 S.OL (VIM F) & 5.7L (VIN 8) DRIVEABILITY AND EMISSIONS
The ECM controls output circuits such as the
injector, IAC, cooling fan relay, etc. by controlling the
ground circuit through transistors in the ECM.
INFORMATION SENSORS
Engine Coolant Temperature Sensor
(Figure
Cl-2)
The coolant sensor is a thermistor (a resistor which
changes value based on temperature) mounted in the
engine coolant stream. Low coolant temperature
produces a high resistance (100,000 ohms at
-4O0C/-
40°F), while high temperature causes low resistance
(70 ohms at
130°C/266"F).
The ECM supplies a 5-volt signal to the coolant
sensor through
a resistor in the ECM and measures
the voltage. The voltage will be high when the engine
is cold, and low when the engine is hot. By measuring
the voltage, the ECM knows the engine coolant
temperature. Engine coolant temperature affects
most systems the
ECM controls.
A failure in the coolant sensor circuit should set
either a Code 14 or Code
15. Remember, these codes
indicate
a failure in the coolant temperature circuit,
so proper use of the chart will lead to either repairing
a wiring problem or replacing the sensor, to properly
repair
a problem.
ENGINE COOLANT TEMPERATURE SENSOR
HARNESS CONNECTOR TO
ECM
4-2-85 LOCKING TAE
Figure C1-2 - Engine Coolant Temperature Sensor
Mass Air Flow (MAF) Sensor
(Figure
C1-3)
The mass air flow (MAF) sensor measures the
amount of air which passes through it.
'l'he ECM uses
this information to determine the operating condition
of the engine, to control fuel delivery.
A large
quantity of air indicates acceleration, while a small
quantity indicates deceleration or idle.
The Bosch mass air flow
(MAF) sensor used in this
vehicle is of the hot wire type. Current is supplied to
the sensing wire to maintain a calibrated
temperature, and as air flow increases or decreases
the current will vary. This varying
of current causes a voltage drop within
the meter circuitry which isdirectly proportional to air
mass. The ECM supplies a current limiting 5-volt
source on the signal line, and the MAF sensor pulls
the voltage low (about
.4V) with low air flow and up to
about 5 volts with high air flow such as
WOT. The
voltage drop is then processed by the ECM for
calculating fuel delivery. If the sensor fails, a Code 33
or 34 should be stored in memory.
Due to the sensor's hot wire being exposed to air,
which always contains some contaminants, there can
be deposits form on the sensing wire. This can affect
the accuracy of the meters measurement. To keep the
system functioning properly, the wire is heated to
about
1000°F after engine shut down. This burn-off
cycle is controlled by the ECM, which energizes the
burn-off relay. The ECM will ground the relay
winding after engine shut down, if the engine had
been running a specified amount of time. With the
relay energized, the ECM then monitors the MAF
signal line to determine if the burn-off function took
place. If it didn't, then a Code 36 will be stored and the
"Service Engine Soon" light will come
"ON" the next
time the engine is started.
Figure C1-3 - Mass Air Flow (MAF) Sensor
Manifold Air Temperature (MAT) Sensor
The air temperature sensor (MAT) is a thermistor
(a resistor which changes value based on temperature)
is mounted in the plenum.
Low temperature produces
a high resistance (100,000 ohms at
-40°C/-40°F) while
high temperature causes low resistance (70 ohms at
130°C/266"F).
The ECM supplies a 5-volt signal to the sensor
through a resistor in the ECM and measures the
voltage. 'l'he voltage will be high when the manifold
air is cold, and low when the air is hot. By measuring
the voltage, the ECM knows the manifold air
temperature

DRIVEABILITY AND EMISSIONS 5.OL (VIN F) & 5.7L (VIN 8) 6E3-C1-3
The MAT sensor signal is used by the ECM to
delay
EGR until the manifold air temperature reaches
about 5°C
(40°F).
A failure in the MAT sensor circuit should set
either a Code
23 or Code 25.
Oxygen (02) Sensor
(Figure
€3-4)
The exhaust oxygen sensor (02) is mounted in the
exhaust system, where it can monitor the oxygen
content of the exhaust gas stream. The oxygen content
in the exhaust reacts with the sensor to produce a
voltage output. This voltage ranges from
approximately
.l volt (high 02 - lean mixture) to .9
volts (low 02 - rich mixture). This voltage can be
measured with a digital voltmeter having at least 10
meg ohms input impedance. Use of standard shop
type voltmeters will result in very inaccurate
readings.
By monitoring the voltage output of the 02 sensor,
the ECM will know what fuel mixture command to
give to the Injector (lean mixture-low
02 voltage= rich
command, rich mixture-high
O2 voltage = lean
command). The
02 sensor, if open, should set a Code 13. A low
voltage in the sensor circuit should set a Code
44. A
high voltage in the circuit should set a Code 45. Codes
44 and 45 could also be set as a result of fuel system
problems. See Code Charts.
EXHAUST OXYGEN (02)
10-2-86
* 45 0078-6E
Figure C1-4 E- xhaust Oxygen (Oz) Sensor
Throttle Position Sensor (TPS)
(Figure C1-5)
The throttle position sensor (TPS) is connected to
the throttle shaft on the throttle body. It is a
potentiometer with one end connected to
5 volts from
the ECM and the other to ECM ground.
A third wire
is connected to the ECM to measure the voltage from
the TPS. As the throttle valve angle is changed
(accelerator pedal moved), the output of the TPS also
changes. At a closed throttle position, the output of the TPS
is low (approximately
.5 volts). As the throttle
valve opens, the output increases so that, at wide-open
throttle, the output voltage should be approximately
5
volts.
By monitoring the output voltage from the
TPS,
the ECM can determine fuel delivery based on throttle
valve angle (driver demand).
A broken or loose 'I'PS
can cause intermittent bursts of fuel from the injector
and an unstable idle, because the ECM thinks the
throttle is moving.
A problem in any of the TPS
circuits will set either a Code
21 or 22. Once a trouble
code is set, the ECM will use an artificial default value
for TPS, and some vehicle perfhrmance will return.
See "On-Car Service" for replacement or
adjustment of
TPS.
10 THROTTLE BODY ASSEMBLY
20 THROTTLE POSITION SENSOR (TPS)
Figure
C1-5 - Throttle Position Sensor
Knock Sensor
This sensor is used to control engine detonation
Refer to Section
"C5", for description.
Vehicle Speed Sensor
The vehicle speed sensor (VSS), part of the digital
cluster, sends a pulsing voltage signal to the ECM,
which the ECM converts to miles per hour.
This
sensor mainly controls the operation of the 'I'CC
system. See Code 24 or Section "C8" for more
information.
ParklNeutral Switch (Auto Only)
The parWneutra1 (PIN) switch indicates to the
ECM when the transmission is in park or neutral.
This information is used for the TCC and the
IAC
valve operation.
Important
Vehicle should not be driven with parklneutral
switch disconnected, as idle quality will be aft'ected
,ind a poss~hle false Code 24 (VSS).

6E3-C1-4 5.0L (VIN F) & 5.7L(VIN 8) DRIVEABILITY AND EMISSIONS
See Section "8A" for more information on the PIN
switch, which is part of the neutrallstart and backup
light switch assembly.
NC "ON" Signal
This signal tells the ECM that the NC selector
switch is turned "ON", and that the pressure cycling
switch is closed. The
ECM uses this to adjust the idle
speed when the air conditioning is working.
[f this signal is not available to the ECM, idle may
be rough, especially when the NC compressor cycles.
The voltage at ECM terminal "B8" should equal
battery voltage on a
C60 system and about 5 volts on a
C68 option, when
NC is requested and the pressure
cycling switch is closed.
Distributor Reference Signal
The distributor sends a signal to the ECM to tell it
both engine rpm and crankshaft position. See ignition
system Section
"C4" for further information.
DIAGNOSIS
To read the codes, use a "Scan" tool or ground the
diagnostic terminal with the engine not running and
the ignition "ON". The "Service Engine Soon" light
will flash Code 12 three times and then flash each code
stored in memory three times. All codes stored in
memory would have been read when Code 12 was
flashed again. No new codes can be stored when in the
diagnostics mode (diagnostics lead grounded). This
eliminates confusion while the system is being worked
on.
To clear the codes from memory:
@ Ignition "OFF".
@ Disconnect battery pigtail, located near the
battery, for 30 seconds.
Since the ECM can have a failure which may
affect only one circuit, following the diagnostic
procedures in this section will determine which circuit
has a problem and where it is.
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:
-
@ There is a problem with the ECM terminal
connections.
- The diagnostic chart will say ECM
connections or ECM. The terminals may have to
be removed from the connector in order to check
them properly.
@ The ECM, or Mem-Cal is not correct for the
application.
- The incorrect components may cause
a malfunction and
may or may not set u code.
@ The problem is intermittent. - 'l'his means that the
problem is not present at the time the system is
being checked. In
this case, refer to the "Symptoms" portion
of the
manual and make a careful physical inspection
of
all portions of the system involved.
@ Shorted solenoid, relay coil, or harness. - 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 BT 8405 testers or equivalent provide a
fast, accurate means of checking for a shorted coil
or a short to battery voltage.
@ The Mem-Cal may be faulty. - Although these
rarely fail, it operates as part of the ECM.
Therefore, it could be the cause
of the problem.
Substitute a known good Mem-Cal.
@ The replacement ECM may be faulty - 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.
ECM
A faulty ECM will be determined in the diagnostic
charts.
MEM-CAL
An incorrect or faulty Mem-Cal, which is part of
the ECM, may set a Code 41 or 52. Also, be sure Mem-
Cal is fully seated and latched in the socket.
ECM INPUTS
A11 of the sensors and input switches can be
diagnosed by the use of
a "Scan" tool. Following is a
short clescription of how the sensors and switches can
he diagnosed
by the use of a "Scan" tool. The "Scan"
can also be used to compare the values for a normal
running engine with the engine you're diagnosing.

DRIVEABILITY AND EMISSIONS 5.OL (VIN F) & 5.7L (VIN 8) 6E3-C1-5
Coolant Temperature Sensor
A "Scan" tool displays engine temperature in
degrees centigrade. After
engine is started, the
temperature should rise steadily to about 90°C then
stabilize when thermostat opens. If the engine has not
been run for several hours (overnight), the coolant
temperature and MAT temperatures should read close
to each other.
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. Voltage
should increase at
a steady rate as throttle is
moved toward WOT (about 4.6 volts).
The ECM has the ability to auto-zero the TPS
voltage if it is below about
.7V (700 mV). This means
that any voltage less than
.7 volts will be determined
by the ECM to be 0% throttle. A failure in the TPS or
circuit should set a Code 21 or 22.
VSS
A "Scan" tools reading should closely match with
speedometer reading with drive wheels turning. A
failure in the VSS circuit should set a Code 24.
MAF Sensor
PIN Switch
A "Scan" tool reads the MAF value and displays it
in grams per second and should read between 4-7 on a
fully warmed up idling engine. Values should change
rather quickly on acceleration, but values should
remain fairly stable
at any given rpm. Most "Scan"
tools will have 2 positions for reading MAF sensor
values (MAF
& air flow). Both values should read the
same if no Code 33 or 34 is set, but if a code is set, the
MAF values will be the default value and the air flow
parameter will lock on the value at which the ECM
recognized the fault.
A failure in the MAF sensor or
circuit should set a Code 33 or 34.
MAT Sensor
A "Scan" tool displays temperature of the air
entering the engine and should read close to 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. A failure in the MAT sensor
circuit should set a Code 23 or 25. The code charts also
contain a chart to check for sensor resistance values
relative to temperature.
02 Sensor
The "Scan" has several positions that will indicate
the state of the exhaust gases,
O2 voltage, integrator,
and block learn. See "Scan" position information in
introduction, Section
"6E".
A problem in the O2 sensor circuit or fuel system
should set
a Code 13 (open circuit), Code 44 (lean
indication), Code 45 (rich indication). Refer to
applicable chart if any of these codes were stored in
memory.
TPS
A "Scan" tool displays throttle position in volts.
The value should read
.54volts f .08 (.46V-.62V),
A "Scan" tool should read "PIN" when in park or
neutral and
"R.D.L." when in Drive. This reading
may vary with different makes of tools. Refer to
CHART
C-1A for PIN switch diagnosis.
NC Request Signal
"Scan" tool should indicate A/C "ON", when AIC is
requested and the pressure cycling switch is closed.
Reference Signal
A "Scan" tool will read this signal and is displayed
in rpm. See Section
"C4" for more information on the
ignition system.
ON-CAR SERVICE
ELECTRONIC CONTROL MODULE (ECM)
Service of the ECR4 should, normally, consist of
either replacement of the ECM or a Mem-Cal change.
If the diagnostic procedures call for the
ECM to be
replaced, the engine calibrator (Mem-Cal) and
ECM
should be checked first to see if they are the cu~ rcct
parts. If they are, remove the Mem-Cal frolri the
faulty ECM and install it in the new service L.:r.'Ni
'I'ITE SERVICE ECM WILL NOT CONTAIN A ME!vI-
CAL. Trouble Code 51 indicates the Mem-Cdi Is
installed improperly or has malfunctioned. W 1 ~:n
Code 51 is obtained, check the Mem-Cal installn(l~in
for bent pins or pins not fully seated in the sockct If
it is installed correctly and Code 51 still
shv 8,
replace the Mem-Cal.
Important
When replacing the production ECM will, :.I
service ECM (controller), it is important to
transfer the broadcast code and production Et'hl
number to the service ECM label.
with throttle closed and ignition "ON", or at iclle.