1988 PONTIAC FIERO check engine

6E3-B-6 5.OL (VIN F) & 5.7L (VIN 8) DRIVEABILITY AND EMISSIONS
POOR FUEL ECONOMY
Definition: Fuel economy, as measured by an actual road test, is
noticeably lower than expected. Also, economy is noticeably lower than it
was on this car at one time, as previously shown by an actual road test.
@ Perform careful visual check as described at
start of Section "B".
@ CHECK:
- Coolant level.
- Engine thermostat for faulty part (always
open) or for wrong heat range. See Section
"6B".
- Compression
- Ignition timing. See Emission Control
Information label.
- TCC for proper operation. A "Scan" should
indicate an rpm drop when the TCC
is
commanded "ON". See CHART C-8.
- Induction system and crankcase for air leaks.
@ Check for exhaust restriction
See CHART
B-1.
DIESELING, RUN-ON
Definition: Engine continues to run after key is
turned off, but runs very roughly. If engine runs
smoothly, check ignition switch and adjustment.
@ Check injectors for leaking. See CHART A-7.
ROUGH, UNSTABLE, OR INCORRECT IDLE, STALLING
Definition: The engine runs unevenly at idle. If bad enough, the car may
shake. Also, the idle may vary in rpm (called "hunting"). Either condition
may be bad enough to cause stalling. Engine idles at incorrect speed.
@ Perform careful visual check as described at
start of Section "B".
e CHECK:
- Throttle linkage for sticking or binding.
- Ignition timing. See emission control
information label.
- ECM ground circuits.
- IAC system. See CHART C-2C.
- Generator output voltage. Repair if less than 9
or more than 16 volts.
- PIN switch circuit. See CHART C-lA, or use
"Scan" tool.
- Injector balance. See CHART C-2A.
- PCV valve for proper operation by placing
finger over inlet hole in valve end several
times. Valve should snap back. If not, replace
valve.
- Evaporative emission control system. CHART
C-3.
- A/C signal to ECM terminal "B8". "Scan" tool
should indicate
AIC is being requested when
ever
A/C is selected and the pressure cycling
switch is closed.
- Minimum idle speed. See Section "C2".
- Loose or damaged MAF sensor duct between
sensor and throttle body. Check
A.I.R. system. There should be no
A.1.R
to ports while in "Closed Loop". See CHART C6.
EGR valve: There should be no EGR at idle.
Run
a cylinder compression check-see Section
"6".
Inspect oxygen sensor for silicon contamination
from fuel, or use of improper RTV sealant. The
sensor will have a white, powdery coating, and
will result in a high but false signal voltage
(rich exhaust indication). The ECM will then
reduce the amount of fuel delivered to the
engine, causing a severe driveability problem.
Check for fuel in pressure regulator hose. If
present replace regulator assembly.
Check ignition system; wires, plugs, rotor, etc.
Check for loose or damaged air duct between
MAF sensor and throttle body.
Disconnect MAF sensor and if condition is
corrected replace sensor.
Clean injectors.
Monitoring block learn 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
1 181, refer to "Diagnostic Aids" on facing page of
Code
45.

DRIVEABILITY AND EMISSIONS 5.OL (VIN F) & 5.7L (WIN 8) 6E3-B-7
EXCESSIVE EXHAUST EMISSIONS OR ODORS
Definition: Vehicle fails an emission test. Vehicle has excessive "rotten egg" smell.
Excessive odors do not necessarily indicate excessive emissions.
@ Perform "Diagnostic Circuit Check."
@ IF TEST SHOWS EXCESSIVE CO AND HC,
(or also has excessive odors):
@ Check items which cause car to run RICH.
@ Make sure engine is at normal
operating temperature.
@ CHECK:
- Fuel pressure. See CHART A-7.
- Incorrect timing. See vehicle emission
control information label.
- Canister for fuel loading. See CHART C-3.
- Injector balance. See CHAR'I' C-2A.
- PCV valve for being plugged, stuck, or
blocked PCV hose, or fuel in the crankcase.
- Spark plugs, plug wires, and ignition
components. See Section
"6D".
- Check for lead contamination of catalytic
converter (look for removal of fuel filler
neck restrictor).
- Check for properly installed fuel cap.
@ If the system is running rich, (block learn
less than
118), refer to "Diagnostic Aids" on
facing page of Code
45.
@ IF TEST SHOWS EXCESSIVE NOx:
@ Check items which cause car to run LEAN,
or to run too hot.
- EGR valve for not opening. See CHART
C-7.
- Vacuum leaks.
- Coolant system and coolant fan for
proper operation. See CHART C-12.
- Remove carbon with top engine cleaner.
Follow instructions on can.
- Check ignition timing for excessive base
advance. See emission control
information label.
@ If the system is running lean, (block learn
greater than
138), refer to "Diagnostic Aids" on
facing page of Code 44.

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.

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-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.

DRIVEABILITY AND EMISSIONS 5.OL (VIN F) & 5.7L (VIN 8) 6E3-C1-7
UPPER RADIATOR
/ MAF SENSOR ASM
1 CLAMP ASM 1.4-2.0 N-rn (1-1.4 LBS. FT.) 1 BOLTISCREW (2)
1 BRACI Figure C1-10 MAF Sensor Service
Install or Connect (Figure C1-9)
1. Mem-Cal in Mem-Cal socket.
Important
Press only on the ends of the Mem-Cal.
Small notches in the Mem-Cal must be aligned
with the small notches in the Mem-Cal socket.
Press on the ends of the Mem-Cal until the
retaining clips snap into the ends of the Mem-Cal.
Do not press on the middle of the Mem-Cal, only
on the ends.
2. Access cover on ECM.
3. ECM in passenger compartment.
4. Connectors to ECM.
5. Right hand hush panel.
6. Negative battery cable.
Functional Check
1. Turn ignition "ON".
2. Enter diagnostics.
A. Allow Code
12 to flash four times to verify no
other codes are present.
This indicates the Mem-Cal is installed
properly and the ECM is functioning.
B. If trouble Code 51 occurs, or if the "Service
Engine Soon" light is "ON" constantly with no
codes, the Mem-Cal is not fully seated or is
defective.
@ If not fully seated, press firmly on the ends
of the Mem-Cal.
If it is necessary to remove the Mem-Cal,
follow the previous removal instructions.
COOLANT SENSOR
NOTICE:
Care must be taken when handling
coolant sensor. Damage to coolant sensor
will affect proper operation of the fuel
injection system.
Remove or Disconnect
1. Negative battery cable.
2. Air inlet duct.
3. Electrical connector.
4. Carefully back out coolant sensor.
Install or Connect
1. Sensor in engine.
2. Electrical connector.
3. Air inlet tube.
4. Negative battery cable.
ENGINE HARNESS ASM
Figure Cl-1 l Relays