1988 PONTIAC FIERO ignition

TABLE OF CONTENTS
............................................................. Before Starting Page B-1
lntermittents .............................................................. PageB-2
HardStart........,........................................................ PageB-2
...................... .................. Surges and/or Chuggle .... ........ ... Page B-3
.............................................. Lack of Power, Sluggish, or Spongy Page 8-3
DetonationISparkKnock ...................................................... PageB-4
...................................................... Hesitation,
Sag, Stumble Page B-4 8 .......................................................... Cuts Out, Misses ? .I Page 8-4
PoorFuelEconomy .......................................................... PageB-5
........................................ Rough, Unstable, or Incorrect Idle, Stalling Page
B-5
............................................. Excessive Exhaust Emissions or Odors Page
B-6
........................................................... Dieseling, Run-on Page B-6
Backfire......,..,.........,............................................... PageB-6
............................. CHART B-1, Restricted Exhaust System Check -All Engines Page B-7
BEFORE
STARTING
Before using this section you should have This check should include:
performed the DIAGNOSTIC CIRCUIT
CHECK. @ Vacuum hoses for splits, kinks, and proper
Verify the customer complaint, and locate the connections,
as shown on Emission Control
correct SYMPTOM below. Check the items Information label.
indicated under that symptom.
@ Air leaks at throttle body mounting and intake
If the ENGINE CRANKS BUT WILL NOT manifold.
RUN, see CHART
A-3. @ Ignition wires for cracking, hardness, proper
Several of the following symptom procedures routing,
and carbon tracking.
call for a careful visual (physical) check.
@ Wiring for proper connections, pinches, and cuts.
The importance of this step cannot be stressed The
following symptoms cover several engines.
too strongly
- it can lead to correcting a problem To
determine if a particular system or component is
without further checks and can save valuable time. used,
refer to the ECCM wiring diagrams for
application .

6EZ-B-2 5.OL (VIN E) 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 Section
"A" for intermittent problems. The fault must be
present to locate the problem. If a fault is
intermittent, use of trouble code charts may result
in replacement of good parts.
@ Most intermittent problems are caused by faulty
electrical connections or wiring. Perform
careful check of suspect circuits for:
- Poor mating of the connector halves, or
terminals, not fully seated in the connector
body (backed out).
I - Improperly formed or damaged terminals.
All connector terminals in problem circuit
should be carefully reformed to increase
contact tension.
- Poor terminal to wire connection. This
requires removing the terminal from the
connector body to check as outlined in the
Introduction to Section
"6E".
@ If a visual (physical) check does not find the
cause of the problem, the car can be driven with
a voltmeter connected to a suspected circuit or a
"Scan" tool may be used. An abnormal voltage
reading, when the problem occurs, indicates the
problem may be in that circuit. If the wiring
and connectors check OK, and a trouble code was
stored for a circuit having a sensor, except
for Codes 44 and 45, substitute a known good
sensor and recheck.
@ Loss of trouble code memory. To check,
disconnect TPS and idle engine until "Service
Engine Soon" light comes
"ON". Code 22 should
be stored, and kept in memory, when ignition is
turned "OFF" for at least 10 seconds. If not, the
ECM
is faulty.
@ An intermittent "SES" light, and no trouble
codes, may be caused by:
- Electrical system interference caused by a
defective relay, ECM driven solenoid, or switch.
They can cause a sharp electrical surge.
Normally, the problem will occur when the
faulty component is operated.
- Improper installation of electrical options, such
as lights, 2-way radios, etc.
- EST wires should be routed away from spark
plug wires, ignition system components, and
generator. Wire for CKT 453 from ECM to
ignition system should be a good ground.
- Ignition secondary shorted to ground.
- CKTs 419 ("SES" light) or 451 (Diagnostic Test)
intermittently shorted to ground.
- ECM power grounds.
HARD START
Definition: Engine cranks OK, but does not start for a long
time. Does eventually run, or may start but immediately dies.
, <
@ CHECK: 4. Connect a radiator test pump to the line and
- For water contaminated fuel. apply 103 kPa (15 psi) pressure. If the
- Fuel system pressure CHART A-7. pressure will hold for 60 seconds, the check
- TPS for sticking or binding should read less than
valve is OK.
1.25 volts on a "Scan" tool. @ Check ignition system for:
- No crank signal; see CHART C-1B. - Proper output with ST-125.
- EGR operation; CHART C-7. - Worn shaft.
- Fuel System - CHART A-7. - Rare and shorted wires.
- For a faulty in-tank fuel pump check valve, - Pickup coil resistance and connections.
which would allow the fuel in the lines to drain
- Loose ignition coil connections.
back to the tank after the engine is stopped. To
- Moisture in distributor cap.
check for this condition:
- Spark plugs, wet plugs, cracks, wear,
1. Ignition "OFF".
improper gap, burned electrodes, or heavy
2. Disconnect fuel line at the filter
deposits.
3. Remove the tank filler cap. @ If engine starts but then, immediately stalls,
open distributor bypass line. If engine then
starts, and runs OK, replace distributor pickup
coil.
@ Check CKT 423 (EST) for short to ground.

DRIVEABILITY AND EMISSIONS 5.OL (VIN E) 6E2-B-3
SURGES AND/OR CHUGGLE
Definition: Engine power variation, under steady
throttle or cruise. Feels like the car speeds up and slows
down, with no change in the accelerator pedal.
@ Use a "Scan" tool to make sure reading of VSS
matches vehicle speedometer. See "Special
Information", Section
"6E".
e CHECK:
- For intermittent EGR at idle. See appropriate
CHART C-7.
- Ignition timing. See Emission Control
Information label.
- Inline fuel filter for dirt or restriction.
- Fuel pressure. See CHART A-7.
- Generator output voltage. Repair if less than 9,
or more than
16 volts.
- TCC Operation. CHART C-8A.
@ Inspect oxygen sensor for silicon contamination
from fuel, or use of improper RTV sealant. The
sensor may have a white, powdery
coabing and
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.
@ Remove spark plugs. Check for cracks, wear,
improper gap, burned electrodes, or heavy
deposits. Also, check condition of the rest of the
ignition system.
LACK OF BOWER, SLUGGISH, OR SPONGY
Definition: Engine delivers less than expected power. Little or no
increase in speed, when accelerator pedal is pushed down part way.
@ Compare customer's car to similar unit. Make - For restricted fuel filter, contaminated fuel or
sure the customer's car has an actual problem. improper fuel pressure. See CHART A-7.
@ Remove air cleaner and check air filter for dirt, - ECM Grounds.
or for being plugged. Replace as necessary.
- EGR operation for being open, or partly open, all
If there is spray from only one injector, then, the time
- CHART C-7.
there is a malfunction in the injector assembly,
- Generator output voltage. Repair if less than 9, or
or in the signal to the injector assembly.
'I'he more than 16 volts.
malfunction can be isolated, by switching the
- Engine valve timing and compression.
injector connectors.
If the problem remains with - Engine, for proper or worn camshaft. See Section
the original injector, after switching the
"6A".
connector, then the injector is defective. Replace - Transmission torque converter operation. See
the injector. If the problem moves with the
Sectionw7A".
injector connector, then the problem is an - Secondary ignition voltage.
improper signal in the injector circuits, see
- Proper operation or ESC. See Section "C5".
CHART A-3. @ Check exhaust system for restriction. See
@ CHECK: CHART B- 1.
- Ignition timing. See Emission Control
Information label.

6EZ-B-4 5.OL (VIN E) DRIVEABILITY AND EMISSIONS
DEWNATION 1 SPARK KNOCK
Definition: A mild to severe ping, usually worse under acceleration. The
engine makes sharp metallic knocks that change with throttle opening.
@ CHECK for obvious overheatingproblems. - For proper transmission shift points. See Section
- Low coolant. "7".
- Loose water pump belt. - TCC operation. See CHART C-8.
- Restricted air flow to radiator, or restricted - For incorrect basic engine parts such as cam,
water flow thru radiator. heads,
pistons, etc.
- Faulty or incorrect thermostat. - Excessive oil entering combustion chamber.
- Coolant sensor, which has shifted in value. @ Remove carbon with top engine cleaner. Follow
- Correct coolant solution - should be a 50150 instructions on can.
mix of GM
#lo52753 anti-freeze coolant (or @ If there is spray from only one injector, then there
equiv.) and water. is
a malfunction in the injector assembly, or in the
@ CHECK: signal to the injector assembly. The malfunction
- For poor fuel quality, proper octane rating. can be isolated by switching the injector
- For correct PROM. connectors. If the problem remains with the
- Spark plugs for correct heat range.
original injector, after switching the connector,
- ESC system opeation. See CHART C-5.
then the injector is defective. Replace the injector.
- Ignition timing. See Vehicle Emission Control
If the problem moves with the injector connector,
Information label. then the
problem is an improper signal in the
- Fuel system for low pressure. See CHART A-7.
injector circuits. See CHART A-3.
- Check EGR svstem. - CHART C-7.
HESITATION, SAG, STUMBLE
Definition: Momentary lack of response as the accelerator is pushed down.
Can occur at all car speeds.
C'sually most severe when first trying to make the car
move, as from a stop sign.
May cause the engine to stall if severe enough.
@ Perform careful visual (physical) check, as Information" label.
described at start of Section
"B". - Generator output voltage. Repair if less than 9 or
@ CHECK: more than 16 volts.
- Fuel pressure. See CHART A-7. - For open ignition system ground, CKT 453.
- Water contaminated fuel. - Canister purge system for proper operation. See
- TPS for binding or sticking.
Section "C3".
- Ignition timing. See "Emission Control - EGR valve operation, CHART C-7.
CU"F OUT, MISSES
Definition: Steady pulsation or jerking that follows engine
speed, usually more pronounced as engine load increases. The
exhaust has a steady spitting sound at idle or low speed.
@ Perform careful visual (physical) check, us
described at start of Section
"B".
@ If ignition system is suspected of causing a miss
at idle or cutting, out under load:
@ Check for missing cylinder by:
1. Disconnect IAC motor. Start engine.
Remove one spark plug wire at a time, using
insulated pliers.
2. If there is an rpm drop on all cylinders, (equal
to within 50
rpm), go to "Rough, Unstable, Or
Incorrect Idle, Or Stalling" symptom.
Reconnect
IAC motor.
3. If there is no rpm drop on one or more
cylinders, or excessive variation in drop, check
for spark, on the suspected
cylinder(s) with J
26792 (ST-1251 spark tester or equivalent. If no
spark, see Section
"6D" for "Intermittent Operation
or Miss". If there is spark, remove spark plug(s) in
these cylinders and check for:
- Cracks
- Wear
- Improper gap
- Burned electrodes
- Heavy deposits
- Perform compression check on
questionable cylinder.
@ Check wire resistance (shoulcl not exceed 30,000
ohms), also, check rotor and distributor cap.

DRIVEABILITY AND EMISSIONS 5.OL (VIN E) 6E2-B-5
@ If the previous checks did not find the problem:
- Visually inspect ignition system for moisture,
dust, cracks, burns, etc. Spray plug wires with
fine water mist to check for shorts.
- Fuel System - Plugged fuel filter, water, low
pressure. See CHART A-7.
- Perform compression check.
- Valve timing.
- Remove rocker covers. Check for bent pushrods,
worn rocker arms, broken or weak valve springs,
worn camshaft lobes. Repair as necessary. See
Section
"6A".
If there is spray from only one injector, then,
there is
a malfunction in the injector assembly,
or in the signal to the injector assembly. The
malfunction can be isolated by switching the
injector connectors. If the problem remains with
the original injector, after switching the
connector, then the injector is defective. Replace
the iniector. If the
~roblem moves with the
injector connector, then, the problem is an
improper signal in the injector circuits. See
CHART A-3.
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.
@ CHECK: @ Visually (physically) check:
- Engine thermostat for faulty part (always open) - Vacuum hoses for splits, kinks, and proper
or for wrong heat range. See Section
"6B". connections, as shown on Vehicle Emission
- Fuel Pressure. See CHART A-7. Control Information label.
@ Check owner's driving habits. - Ignition wires for cracking, hardness, and proper
- Is A/C "ON" full time (Defroster mode "ON")? connections.
- Are tires at correct pressure? e Check ignition timing. See Emission Control
- Are excessively heavy loads being carried? Information label.
- Is acceleration too much, too often? @ Remove spark plugs. Check for cracks, wear,
- Suggest driver read "Important Facts on Fuel
improper gap, burned electrodes or heavy deposits.
Economy" in owner's manual. Repair
or replace, as necessary.
@ Perform "Diagnostic Circuit Check". @ Check compression. See Section "6A".
@ Check air cleaner element (filter) for dirt or @ Check TCC for proper operation. See CHART C-8.
being plugged. Use "Scan"
tool if available.
@ Check for proper calibration of speedometer. @ Check for dragging brakes.
Suggest owner fill fuel tank and recheck fuel
economy.
@ Check for exhaust system restriction. ,
See CHART B-1.
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 severe enough to cause stalling. Engine idles at incorrect speed.
@ CHECK: - Vacuum leaks can cause higher than normal
- Ignition timing. See Emission Control idle.
Information label.
- EGR "ONJ', while idling, will cause roughness,
- PIN switch circuit. See CHART C-1 A. stalling, and hard starting. CHART C-7.
- For injectorb) leaking. Check fuel pressure, - Battery cables and ground straps should be clean ,
CHART A-7. and secure. Erratic voltage will cause IAC to
- IAC - See CHART C-2C.
change its position, resulting in poor idle quality.
- If a sticking throttle shaft or binding linkage - IAC valve will not move, if system voltage is
causes
a high TPS voltage (open throttle
below 9, or greater than 17.8 volts.
indication), the ECM will not control idle.
- Use "Scan" tool to determine if ECM is receiving
Monitor TPS voltage. "Scan"
andlor voltmeter AlC request signal.
should read less than
1.2 volts with throttle
closed.

6E2-8-6 5.OL (VIN E) DRIVEABILITY AND EMISSIONS
- MAP Sensor - Ignition "ON", engine stopped.
Compare MAP voltage with known good vehicle.
-
Voltage should be the same + 400 mV (.4 volts).
OR
Start and idle engine. Disconnect
sensor
electrical connector. If idle improves, substitute
a known good sensor and recheck.
- A/C refrigerant pressure too high. Check for
overcharge or faulty pressure switch.
- PCV valve for proper operation by placing finger
over inlet hole in valve end several times. Valve
should snap back. If not, replace valve.
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.
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 that will cause engine to run
RICH.
e Make sure engine is at normal operating
temperature.
o CHECK:
- Fuel pressure. See CHART A-7.
- Incorrect timing. See Vehicle Emission
Control Information label.
- Canister for fuel loading. See CHART C-3.
- 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
1181, refer to "Diagnostic Aids" on facing
page of Code
45.
o 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.
DIESELING, RUN-ON
Definition: Engine continues to run after key is turned "OFF", but runs very roughly.
Ifengine runs smoothly, check ignition switch and adjustment.
@ Check injector for leaking. Apply 12 volts to fuel Visually check injector and TBI assembly for fuel
pump test terminal to turn "ON" fuel pump and leakage.
pressurize fuel system.
BACKFIRE
Definition: Fuel ignites in intake manifold, making a loud popping noise.
@ CHECK: - For faulty spark plugs and/or plug wires or
- EGR operation for being open all the time. See
hoots.
CHART C-7. - Faulty A.I.R. check valve.
- Output voltage of ignition coil. @ Perform a compression check - look for sticking or
- For crossfire between spark plugs (distributor leaking valves.
cap, spark plug wires, and proper routing' of plug
- For proper valve timing.
wires).
- Broken or worn valve train parts.
- Engine timing - See Emission Control
Information label.

6EZ-C-1 5.OL (VIN E) DRIVEABILITY AND EMISSIONS
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 C1-1
@ C2 Fuel Control System - TBI 200 .......................................... Page C2-1
Evaporative Emission Control System (EECS) ...............................
Ignition System 1 EST ................................................
Electronic Spark Control (ESC) System ...................................
Air Injection Reaction (A.I.R.) System ....................................
Exhaust Gas Recirculation (EGR) System ..................................
Transmission Converter Clutch (TCC) System ..............................
Positive Crankcase Ventilation (PCV) ...................................
Thermostatic Air Cleaner (THERMAC) ...................................
BIAGNOSIIC CHARTS
Page C3-1
Page C4-1
Page C5-1
Page C6-1
Page C7-1
Page C8-1
Page C13-1
Page C14-1
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 Diagnosis ................................... Page C1-12
@ Chart C-1B Crank Signal ................................................ Page C1-14
@ Chart C-1 D MAP Output Check ........................................ Page C1-16 I
..................... @ Chart C-1 E Power Steering Pressure Switch (PSPS) Diagnosis Page C1-18 1
................................ @ Chart C-2C Idle Air Control (IAC) Valve Check Page C2-16 !
..................................... @ Chart C-3 Canister Purge Valve Check Page C3-4 I
@ Chart C-4 Ignition System Check ......................................... Page C4-4
........................ @ Chart C-5 Electronic Spark Control (ESC) System Check Page C5-4
- ............................. @ Chart C-6 AIR Management Check Pedes Valve Page C6-6
............................. Chart C-7 Exhaust Gas Recirculation (EGR) Check Page C7-4
@ Chart C-8A Transmission Converter Clutch (TCC) Electrical Diagnosis (1 of 2) ......... Page C8-4 I
@ Chart C-8A 700-4R Transmission Electrical Diagnosis (2 of 2) ..................... Page C8-6 I
......................... @ Chart C-8B Manual Transmission Shift Light Diagnosis Page C8-8

DRIVEABILPTY AND EMISSIONS 5.QL (VIN E) 6E2-C"1-3
MAT SENSOR (TYPICAL)
Figure C1-5 - MAT Sensor - Typical
When manifold pressure is high, vacuum is low. The
MAP
sensor is also used to measure barometric
pressure under certain conditions, which allows the
ECM to automatically adjust for different altitudes.
The ECM sends a 5-volt reference signal to the
MAP sensor. As the manifold pressure changes, the
electrical resistance of the sensor also changes. By
monitoring the sensor output voltage, the ECM knows
the manifold pressure. A higher pressure, low vacuum
(high voltage) requires more fuel, while a lower
pressure, higher vacuum (low voltage) requires less
fuel.
The
ECM uses the MAP sensor to control fuel delivery
and ignition timing.
A failure in the
MAP sensor circuit should set a
Code 33 or Code 34.
Manifold Air Temperature (MAT) Sensor
The manifold air temperature sensor (MAT) is a
thermistor, a resistor which changes value based on
the temperature of air entering the enigne. Low
temperature produces
a high resistance ( 100,000 ohms
at
- 40°C I- 40°F), while high temperature causes low
resistance (70 ohms at 130°C
I 226°F). The ECM
supplies a
5 volt signal to the sensor through a resistor
in the ECM and measures the voltage. The voltage
will be high when the intake air is cold and low when
the air is hot. By measuring the voltage, the ECM
knows the manifold air temperature.
The MAT sensor is also used to control spark
timing and to delay EGR when
intake air is cold.
A failure in the
MAT sensor circuit should set
either a Code 23 or Code 25.
Oxygen (02) Sensor
The exhaust oxygen sensor is mounted in the
exhaust system where it can monitor the
oxygen
content of the exhaust gas stream.
EXHAUST OXYGEN (02)
Figure C1-6 - Exhaust Oxygen (Oz) Sensor
The oxygen content in the exhaust reacts with the
oxygen sensor to produce a voltage output. This
voltage ranges from approximately
.1 volts (high 02 -
lean mixture) to .9 volts (low 02 - rich mixture).
By monitoring the voltage output of the O2 sensor,
the ECM will know what fuel mixture command to
give to the injector (lean mixture
- low voltage - rich
command, rich mixture
- high voltage - lean
command). 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.
'I'he 02 sensor, if open, should set a Code 13. A
shorted sensor circuit should set
a Code 44. A high
voltage in the circuit should set a Code 45. When any
of these codes are set, the car should run in the "Open
Loop" mode.
Throttle Position Sensor (TPS)
The throttle position sensor ('I'PS) is connected to
the throttle shaft on the
TBI unit (see Figure C1-7). It
is a potentiometer with one end connected to 5 volts
from the ECM and the other to 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).If the sensor CKT is open,
the ECM will set a Trouble Code 22. If the circuit is
shorted, the ECM will think the vehicle is at WOT,
and a Trouble Code 21 will be set.