1988 PONTIAC FIERO turn signal

6EZ-C1-4 S.OL (VIN E) DRIVEABILITY AND EMISSIONS
THROTTLE VALVE
ENGINE CONTROL MODULE (ECM)
THROTTLE POSITION
(TPS)
8P 0321.
Figure C1-7 - Throttle Position Sensor (Typical)
A brolten or loose TPS can cause intermittent bursts of
fuel from the injector, and an unstable idle, because
the ECM thinks the throttle is moving. Once a trouble
code is set, the ECM will use an artificial value for
TPS, and some vehicle performance will return.
On all engines, the TPS is not adjustable. The
ECM uses the reading at idle for the zero reading, so
no adjustment is necessary.
Knock Sensor
The knock sensor is mounted in the engine block.
When abnormal engine vibrations (spark knock) are
present, the sensor produces a voltage signal, which is
sent to the ESC module.
See Section
"C5" for further information on the
electornic spark control
(ESC) system.
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 affected
and a possible false Code
24 VSS.
See Section
"8A" for more information on the PIN
switch, which is part of the neutrallstart and
backup light switch assembly.
Crank Signal
The ECM looks at the starter solenoid to tell when
the engine is cranking. It uses this to tell when the car
is in the Starting Mode.
If this signal is not available, car may be hard to
start in extremely cold weather.
AIC Request Signal
This signal tells the ECM that the AJC 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.
Vehicle Speed Sensor (VSS)
The vehicle speed sensor (VSS) sends a pulsing
voltage signal to the ECM, which the ECM converts to
miles per hour. This sensor mainly controls the
operation of the TCC system. See "TCC System" for
more information.
Distributor Reference Signal
The distributor sends a signal to the ECM to tell it
both engine rpm and crankshaft position. See "EST
System" for further information.
Power Steering Pressure Switch (PSPS)
I
This switch tells the ECM that the vehicle is in a
parking maneuver.
The ECM uses this information to
compensate for the additional engine load by moving
the IAC valve. The ECM will, also, turn
"OFF" the
A/C clutch when high pressure is detected.
( POWER STEERING PRESSURE SWITCH
Figure C'I-8 - Power Steering Pressure Switch (PSPS)

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

6EZ-C1-6 5.OL (VIN E) DRIVEABILITY AND EMISSIONS
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.
MAP Sensor
A "ScanJ' tool reads manifold pressure and will
display either volts or
kPa of pressure.
Key "ONJ', engine stopped, (no vacuum), MAP will
read high voltage or pressure, while at idle
(highvacuum), MAP will read low voltage or pressure.
Likewise, on accel., MAP will read high and on decel.,
will read low.
A failure in the MAP sensor, or circuit, should
result in a Code 33 or 34.
Oxygen (02) Sensor
The "Scan" tool has several positions that will
indicate the state of the exhaust gases,
02 voltage,
integrator, and block learn. See "Scan" tool position
information in the Introduction of Section
"6E".
A problem in the O2 sensor circuit should set a
Code 13 (open circuit), Code
44 (lean 02 indication),
Code
45 (rich 02 indication). Refer to the applicable
chart, if any of these codes were stored in memory.
Throttle Position Sensor (TPS)
A "Scan" tool displays throttle position in volts.
The
5.OL should read under 1.25 volts, with throttle
closed and ignition on, or at idle. Voltage should
increase at a steady rate as throttle is moved toward
WOT. The ECM has the ability to Auto-Zero the TPS
voltage, if it is below about 1.25 volts. This means
that any voltage less than 1.25 volts volts will be
determined by the ECM to be
0% throttle. Some
"Scan" tools have the ability to read the percentage of
throttle angle and should read
0%, when the throttle
is closed.
A failure in the TPS circuit or TPS, should
set a Code 21 or 22.
Vehicle Speed Sensor (VSS)
A "Scan" tool reading should closely match with
speedometer reading, with drive wheels turning. A
failure in the VSS circuit should set a Code
24.
PIN Switch
A "Scan" tool should read "ON", when in park or
neutral and "OFF", when in drive. This reading may
vary with different makes of tools. Refer to CHART C-
IA for
PIN switch diagnosis.
Power steering Pressure Switch (POPS)
A Scan" tool should read "OFF" normally, and
"ON" with high pressure. This reading may vary with
different makes of tools. Refer to CHART
C-1E for
PSPS diagnosis.
NC Request Signal
If the low pressure switch is closed and AIC is
"ON", the "Scan" tool should indicate
A/C "ON".
Distributor Reference Signal
A "Scan" tool will read this signal and is displayed
in rpm. See Section
"C4", for more information on the
Ignition System
.
Knock Signal
A "Scan" tool will indicate when the ESC module
signals the ECM that knock is present. See Section
"C5" for further information on the ESC System.
ON-CAR SERVICE
ELECTRONIC CONTROL MODULE (ECM)
Service of the ECM should normally consist of
either replacement of the ECM or a PROM change.
If the diagnostic procedures call for the ECM to be
replaced, the engine calibrator (PROM) and ECM
should be checked first to see if they are the correct
parts. If they are, remove the PROM from the faulty
ECM and install it in the new service ECM. THE
SERVICE ECM
WILL NOT CONTAIN A PROM.
Trouble Code "51" indicates the PROM is installed
improperly or has malfunctioned. When Code "51" is
obtained, check the PROM installation for bent pins or
pins not fully seated in the socket. If the PROM is
installed correctly and Code
"51" still shows, replace
the PROM.
Important
When replacing the production ECM with a
service ECM (controller), it is important to
transfer the Broadcast code and production ECM
number to the service ECM label. Please do not
record on ECM cover. This will allow positive
identification of ECM parts throughout the service
life of the vehicle.

DRIVEABILIW AND EMISSIONS - 5.OL (VIN E) 6E2-62-1
SECTION C2
FUEL CONTROL SYSTEM
TBI MODEL 228
CONTENTS
GENERAL DESCRIPTION . . . . . . . . . . . . . . . C2-1
PURPOSE ......................... C2-1
MODES OF OPERATION . . . . . . . . . . . . . . C2-1
Starting Mode . . . . . . . . . . . . . . . . . . . C2-1
Clear Flood Mode . . . . . . . . . . . . . . . . C2-2
RunMode . . . . . . . . . . . . . . . . . . . . . . C2-2
Open Loop . . . . . . . . . . . . . . . . . . . . . . C2-2
Closed Loop . . . . . . . . . . . . . . . . . . . . . C2-2
Acceleration Mode . . . . . . . . . . . . . . . C2-2
Deceleration Mode . . . . . . . . . . . . . . . C2-2
Battery Correction Mode . . . . . . . . . . . C2-2
Fuel Cut Off Mode . . . . . . . . . . . . . . . . C2-2
FUEL CONTROL SYSTEM COMPONENTS
. . . C2-2
BASIC SYSTEM OPERATION . . . . . . . . . . . C2-3
THROTTLE BODY INJECTION (TBI) UNIT. . . C2-3
Fuel Injectors . . . . . . . . . . . . . . . . . . . . C2-3
Pressure Regulator . . . . . . . . . . . . . . . C2-3
ldle Air Control (IAC) Valve . . . . . . . . . . C2-4
Throttle Position Sensor (TPS) . . . . . . . . C2-4
FUEL PUMP.. . . . . . . . . . . . . . . . . . . . . . . C2-5
FUEL PUMP ELECTRICAL CIRCUIT . . . . . . . C2-5
DIAGNOSIS . . . . . . . . . . . . . . . . . . . . . . * C2-5
FUEL CONTROL . . . . . . . . . . . . . . . . . . . . C2-5
GENERAL DESCRIPTION
PURPOSE
The basic function of the fuel control system is to
control fuel delivery to the engine. Fuel is delivered to
the engine by
a throttle body injection ('FBI) unit.
ENGINE CONTROL MODULE (ECM)
EXHAUST OXYGEN (0,) SENSOR
I 1 THROTTLE BODY INJECTION UNIT (TBI)
CATALYTIC CONVERTER
8P 0352 SYE a 3 81
Figure C2-1 - Closed Loop System
ldle Air Control Valve (IAC) . . . . . . . . . C2-5
Driveability . . . . . . . . . . . . . . . . . . . .. C2-5
ON VEHICLE SERVICE
. . . . . . . . . . . . . . . . . C2-5
GENERAL SERVICE INFORMATION . . . . . . C2-5
Fuel Pressure Relief . . . . . . . . . . . . . . . C2-7
Fuel System Pressure Test . . . . . . . . . . . C2-7
Cleaning and Inspection . . . . . . . . . . . C2-7
Thread Locking Compound . . . . . . . . . C2-7
FUEL METER COVER ASSEMBLY . . . . . . . . C2-7
FUEL INJECTOR ASSEMBLIES . . . . . . . . . . C2-8
FUEL METER BODY ASSEMBLY . . . . . . . . . C2-9
THROTTLE POSITION SENSOR (TPS) . . . . . C2-10
IDLE AIR CONTROL (IAC) VALVE . . . . . . . . C2-11
THROTTLEBODYASSEMBLY .......... C2-11
MINIMUM IDLE SPEED CHECK.. . . . . . . . . C2-12
THROTTLE BODY INJECTION (TBI) UNIT.. . C2-I3
FUEL HOSEIPIPE ASSEMBLIES . . . . . . . . . . C2-13
Materials . . . . . . . . . . . . . . . . . . . . . . C2-13
Fuel Line Repair . . . . . . . . . . . . . . . . . . C2-13
FUEL PUMP RELAY . . . . . . . . . . . . . . . . . . C2-13
OIL PRESSURE SWITCH . . . . . . . . . . . . . . . C2-13
PARTS INFORMATION
. . . . . . . . . . . . . . . . . C2-14
The main control sensor is the oxygen (02) sensor,
which is located in the exhaust manifold. The
O?
sensor tells
the engine control module ECM the
amount of osygen in the exhttust gas, and the ECM
changes the airtfuel ratio to the engine by controlling
the fuel injector.
A 14.7: 1 aidfuel ratio is required for
efficient catalytic converter operation. Because of the
constant measuring and adjusting of the
airlfuel ratio,
the fuel injection system is called a "Closed
IAoopP
System (Figure C2 -1).
MODES OF OPERATION
The ECM monitors voltages from several sensors
to determine how
much fuel to give the engine. The
fuel is delivered under one of several conditions, called
"modes." All the modes are controlled by the ECM.
Starting Mode
When the key is first turned "ON", the ECM turns
on the fuel pump relay for two seconds,
i~nd the l'uel
pump builds up pressure to the TRI unit. The ECM
checks the coolant
temperature sensor, throttle
position sensor
('UPS), manifold absolute pressure
(MAP) sensor, and crank signal, then determines the
proper airtfuel ratio tbr starting. This ranges from

6EZ-C2-2 DRIVEABILITY AND EMISSIONS - 5.8b (VIN E)
1.5:1 at -36°C (-33°F) to 14.7:1, at 94°C (201°F)
running temperature.
The ECM controls the amount of fuel delivered in
the starting mode by changing how long the injector is
turned "ON" and "OFF". This
is done by "pulsing" the
injector for very short times.
Clear Flood Mode
If the engine floods, clear it by pushing the
accelerator pedal down all the way. The ECM then
pulses the injector at a
20:1 airlfuel ratio, and holds
this injector rate as long as the throttle stays wide
open, and the engine is below 600 rpm. If the throttle
position becomes less than
80%, the ECM returns to
the starting mode.
Run Mode
The run mode has two conditions called "Open
Loop" and "Closed Loop."
Open Loop
When the engine is first started, and it is above
400 rpm, the system goes into "Open Loop" operation.
In "Open Loop," the ECM ignores the signal from the
(02) sensor, and calculates the airlfuel ratio based on
inputs from the coolant temperature and MAP
sensors.
The system stays in "Open Loop" until the
following conditions are met:
1. The
O2 sensor has varying voltage output,
showing that it is hot enough to operate properly.
(This depends on temperature.)
2. The coolant temperature sensor is above a
specified temperature.
3. A specific amount of time has elapsed after
starting the engine.
Closed Loop
The specific values for the above conditions vary
with different engines, and are stored in the
programmable read only memory (PROM). When
these conditions are met, the system goes into "Closed
Loop" operation. In "Closed Loop," the ECM
calculates the
aidfuel ratio (injector on-time) based on
the signal from the
O2 sensor. This allows the aidfuel
ratio to stay very close to 14.7:1.
Acceleration Mode
The ECM looks at rapid changes in throttle
position and manifold pressure, and provides extra
fuel.
Deceleration Mode
When deceleration occurs, the fuel remaining in
the intake manifold can cause excessive emissions and
backfiring. Again, the ECM looks at changes in
throttle position and manifold pressure and reduces
the amount of fuel. When deceleration is very fast, the
ECM can cut off fuel completely for short periods.
Battery Voltage Correction Mode
When battery voltage is low,
the ECM can
compensate for a wealc spark delivered by the
distributor by:
@ Increasing injector on time of fuel delivered;
@ Increasing the idle rpm.
Fuel Cutoff Mode
No fuel is delivered by the injectors when the
ignition is "OFFJ'. This prevents dieseling. Also, fuel
is not delivered if no reference pulses are seen from
the distributor, which means the engine is not
running.
Fuel cutoff also occurs at high engine
rpm, to protect internal engine components from
damage.
FUEL CON"%ROL SYSXM
COMPONENTS
The fuel control system consists of the following:
@ Throttle body injection (TBI) unit
@ Fuel pump
Fuel pump relay.
FUEL PUMP AND
SENDING UNIT
FUEL SUPPLY LINE
16 FUEL RETURN LINE
Figure C2-2 - Fuel Control System

6EZ-C2-4 DRIVEABILITY AND EMISSIONS - 5.OL (VIN El
[isj FUEL METER COVER bL BODY ASSEMBLIES
1 THROTTLE BODY ASSEMBLY
1 IDLE AIR CONTROL VALVE ASSEMBLY - FILTERED AIR INLET
PlNTLE
TWRO$TLE VAWE
VACUUM PORTS - FOR ENGINE OR EMISSION
CONTROLS
8P 0319-SY 111 5W7
Figure C2-5 - ldle Air Contol System
ldle Air Control (IAC) Valve
The purpose of the idle air control (IAC) valve , is
to control engine idle speed, and prevent stalls due to
changes in engine load (see Figure
C2-5) .
The IAC valve, mounted on the throttle body,
controls bypass air around the throttle valve By
moving a conical valve IN (to decrease air flow) or
OUT (to increase air flow), a controlled amount of air
can move around the throttle valve. If rpm is too low,
more air is bypassed around the throttle valve to
increase rpm.
11 rpnl is too high, less air is bypassed
around the
throt:le valve to decrease rpm.
The IAC valve moves in small steps called
"Counts," and can be monitored by
a "Scan" tool which
plugs into the assembly line data
link (ALDI,)
connector
During idle, the proper position of the IAC valve is
calculated by the ECM based on battery voltage,
coolant temperature,
ellgine load, and engine rpm. If
the rpm drops below a specified rpm, and the throttle
valve is closed, the ECM senses a near stall condition.
The ECM will then calculate a new IAC valve position
to prevent stalls.
If the IAC valve is disconnected or connected with
the engine running, the idle
rpnl may he wrong. In
this case, the
IAC valve may he reset by turning the
ignition switch "ON" and
"OFF" one time
'I'he IAC valve affects only the idle characteristics
of the engine
If it i.; ol)cltl fullv, too much ,LII. tc 111 I)(>
BALL BEARING ASSEMBLY -
STATOR ASSEMBLY
ROTOR
ASSEMBL
I
SPRING
PlNTLE
LEAD SCREW A
Figure C2-6 - ldle Air Control (IAC) Valve
allowed to the manifold and idle speed will he high. if
it is stuck closed, too little air will be
allo\verl in the
manifold, and idle speed will be too low. If it is stuck
part way open, the idle may be rough, and will not
respond to engine load changes.
On
4.3L (VIN Z) V6, LB4 engines, for "B" and "G"
cars, the valve is thread mounted, with a dual taper,lO
mm diameter pintle (Figure C2-6). If replacement is
necessary, use only an IAC valve with the correct part
number and appropriate pintle shape and diameter.
I THROTTLE VALVE
ENGINE CONTROL MODULE (ECM)
,q
THROTTLE POSITION
SENSOR (TPS)
Figure C2-7 - Throttle Position Sensor
Throttle Position Sensor (TPS)
The throttle position sensor ('I'PS), is mounted on
the side of the throttle body opposite the throttle lever
assembly. Its function is to sense the current throttle
valve position
and relkly that information to the ECM
(Figure (22-7). Knowledge of throttle position allows
lhe ECM to generate the recluired i~jector control
signals (base pulse). If the 'I'PS senses a wide open
throttle,
a voltc\ge sic,ll,~I il~tlic~ttinq this condition 13

6E2-CZ-16 DRIVEABILITY AND EMISSIONS - 5.OL (WIN E)
CHART C-2C
IDLE AIR CONTROL (IAC) VALVE CHECK
5.OL (VIN E) "F'" SERIES (TBI)
Circuit Description:
The ECM controls idle rprn with the IAC valve. To increase idle rpm, the ECM moves the IAC valve out,
allowing more air to pass by the throttle plate. To decrease rpm, it moves the IAC valve in, reducing air flow by
the throttle plate. A "Scan" tool will read the
ECM commands to the IAC valve in counts.
The higher the
counts, the more air allowed (higher idle). The lower the counts, the less air allowed (lower idle).
Test Description: Numbers below refer to circled
numbers on the diagnostic chart.
1. Continue with test, even if engine will not idle. If
idle is to low, "Scan" will display 80 or more
counts, or steps. If idle is high, it will display
"0"
counts. Occasionally, an erratic or unstable idle
may occur.
Engine speed may vary 200 rpm, or
more, up and down. Disconnect IAC. If the
condition is unchanged, the IAC is not at fault.
2. When the engine was stopped, the IAC Valve
retracted (more air) to a fixed "Park" position for
increased air flow and idle speed during the next
engine start. A "Scan" will display 100 or more
counts. When performing this test, immediately
note rprn on start up, because, on a warm engine,
the rprn will decrease rapidly.
3. Be sure to disconnect the IAC valve prior to this
test.
The test light will confirm the ECM signals
by
a steady or flashing light on all circuits.
4. There is a remote possibility that one of the
CKTs
is shorted to voltage, which would have been
indicated by a steady light. Disconnect ECM and
turn the ignition
"ON" and probe terminals to
check for this condition.
Diagnostic Aids:
A slow unstable idle may be caused by a system
problem that cannot be overcome by the
IAC. "Scan"
counts will be above 60 counts, if too low,
and "0"
counts, if engine speed is too high.
If idle is too high, stop engine. Ignition "Oh'".
Ground diagnostic terminal. Wait 30 seconds for
IAC to seat, then, disconnect IAC. Lnground
diagnostic terminal and start engine. If idle speed is
above 450 rprn in drive, locate and correct vacuum
leak. If rpm is less than 450 rpm,
ad,jrlst minimum
idle speed, or correct other conditions, which may
affect idle. refer to Rough Unstable or Incorrect Idle,
in Symptoms, Section
"R".
@ System too lean (Hi.gh AirJFuel Ratio)
Idle speed may be too high or too low. Engine
speed may vary up and down, disconnecting IAC
does not help. May set Code
33.
"Scan" and/or Voltmeter will read an oxygen
sensor output less than 300 mv
(.3 volts). Check
for low regulated fuel pressure or water in
fuel. A
lean exhaust, with an oxygen sensor outpirt fixed
above 800
mv (.8 volts), will be a contaminated
sensor, usually silicone. This may also set
a Code
45.
@ System too rich (Low AirIFuel Ratio)
Idle speed too low. "Scan" counts usually above
80. System obviously rich and may exhibit black
srnoke exhaust.
"Scan" tool and/or Voltmeter will
read an oxygen
sensor signal fixed above 800
mv (.8 volts).
Check:
- High fuel pressure
- Injector leaking or sticking
@ Throttle Body. Remove IAC and inspect bore for
foreign material or evidence of
IAC valve
dragging the bore.
@ If above ;
e all OK, refer to "Rough, Unstable,
Incorrect Idle or Stalling", in Symptoms, Section
"I<".

DRIVEABILITY AND EMISSIONS 5.8L (VIN E) 6EZ-C3-1
SECTION C3
EVAPORATIVE EMISSION CONTROL SVSEENI (EECS)
CONTENTS
........................ GENERAL DESCRIPTION ............... C3-1 DIAGNOSIS C3-2
.......... PURPOSE ........................ C3-1 VISUAL CHECK OF CANISTER C3-2
.......... VAPOR CANISTER.. ................. C3-1 CANISTER PURGE SOLENOID C3-2
................. EVAPORATIVE EMISSION SYSTEM.. ..... C3-1 ON-CAR SERVICE C3-2
............ IN-TANK PRESSURE CONTROL VALVE . . C3-2 FUEL VAPOR CANISTER R/R C3-2
.................. RESULTS OF INCORRECT OPERATION .... C3-2 CANISTER HOSES.. C3-2
................ PARTS INFORMATION C3-2
GENERAL DESCRIPTION
PURPOSE
The basic evaporative emission control system
(EECS) used on all vehicles is the charcoal canister
storage method. This method transfers fuel vapor
from the fuel tank to an activated carbon (charcoal)
storage device (canister) to hold the vapors when the
vehicle is not operating. When the engine is running,
the fuel vapor is purged from the carbon element by
intake air flow and consumed in the normal
combustion process.
VAPOR CANISTER
Gasoline vapors from the fuel tank flow into the
tube labeled tank. Any liquid
fuel goes into a
reservoir in the bottom of the canister to protect the
integrity of the carbon bed above (Figure C3-1). These
vapors are absorbed into the carbon. The canister is
purged when the engine is running above idle speed.
Ambient air is allowed into the canister through the
air tube in the top. The air mixes with the vapor and
the mixture is drawn into the intake manifold.
EVAPORATIVE EMISSION SYSTEM
The canister is equipped with a normally closed
(N/C) solenoid to control canister purge. The ECM
operates the solenoid which controls vacuum to the
purge valve in the charcoal canister. Under cold
engine or idle conditions, the solenoid is turned "OFF"
by the ECM, which closes the solenoid and blocks
vacuum to the canister purge valve.
The ECM turns "ON" the solenoid valve and allows
purge when:
@ Engine is warm.
@ After the engine has been running a specified
time.
@ Above a specified road speed.
@ Above a specified throttle opening.
TANKTUBE LQUID FUEL AREA
INLET AIR VAPOR STORAGE AREA
PURGE TUBE PURGE
SOLENOID
Figure C3-1 - Inverted Function Vapor Canister -
With Encapsulated Purge Solenoid
This is an ECM feedback system that increases
purge until the ECM senses a rich condition from the
oxygen sensor. The purge
is then regulated until the
ECM no longer receives a rich signal from the
O2
sensor. This system uses an in-tank pressure control
valve to control the flow of vapors from the fuel tank to
the canister.