CHEVROLET PLYMOUTH ACCLAIM 1993 Service Manual

(1) Before installing an injector, lubricate O-ring
with a drop of clean engine oil. (2) Being careful not to damage the O-ring, install
injector top end into fuel rail receiver cup. (3) Install injector lock ring by sliding open end
into slot of the injector and onto the receiver cup
ridge into the side slots of ring (Fig. 8). (4) Repeat steps for remaining injectors.
(5) Install injector wiring harness to injectors and
fasten into wiring clips (Fig. 10).
FUEL PRESSURE REGULATOR
WARNING: RELEASE FUEL SYSTEM PRESSURE
BEFORE SERVICING FUEL SYSTEM COMPONENTS.
WHEN SERVICING FLEXIBLE FUEL VEHICLES,
WEAR METHANOL RESISTANT GLOVES AND EYE PROTECTION AND AVOID BREATHING FUMES. DO
NOT ALLOW METHANOL/GASOLINE MIXTURES TO
CONTACT SKIN. SERVICE VEHICLES IN WELL VEN-
TILATED AREAS AND AVOID IGNITION SOURCES.
NEVER SMOKE WHILE SERVICING THE VEHICLE.
REMOVAL
(1) Perform fuel system pressure release procedure.
(2) Disconnect negative cable from battery.
(3) Disconnect vacuum hose from fuel pressure reg-
ulator (Fig. 11).
Place a shop towel under fuel pressure regula-
tor to absorb any fuel spillage. (4) Use 2 tubing wrenches, to loosen the line nut
on the fuel return tube (Fig. 12).
(5) Remove fuel pressure regulator mounting nuts
(Fig. 11). (6) Lift pressure regulator up out of fuel rail (Fig.
13). Ensure the O-ring and spacer were removed
with the regulator. Discard O-Ring.
Fig. 9 Fuel Rail and Injector Assembly
Fig. 10 Fuel Rail Assembly
Fig. 11 Servicing Fuel Pressure Regulator
Fig. 12 Removing Fuel Return Tube
Ä FUEL SYSTEMS 14 - 81

INSTALLATION
WARNING: THE FUEL PRESSURE REGULATOR,
O-RING AND SPACER DESIGNED FOR GASOLINE
ONLY VEHICLES CANNOT BE USED ON FLEXIBLE
FUEL AA-BODY VEHICLES. WHEN SERVICING THE
FUEL SYSTEM OF A FLEXIBLE FUEL VEHICLE,
ONLY USE ORIGINAL EQUIPMENT OR EQUIVA-
LENT REPLACEMENT COMPONENTS.
(1) Lubricate new O-ring with a drop of clean en-
gine oil. Install spacer and O-ring into the receiver
cup on fuel rail (Fig. 13). (2) Install mounting nuts. Tighten nuts to 7 N Im
(65 in. lbs.) torque. (3) Connect fuel return tube to pressure regulator.
Using a wrench to hold the fuel pressure regulator,
tighten the nut to 28 N Im (150 in. lbs.) torque.
(4) Connect vacuum hose to pressure regulator. Re-
place clamp. (5) Connect negative cable to battery.
CAUTION: When using the ASD Fuel System Test,
the Auto Shutdown (ASD) Relay remains energized
for either 7 minutes, until the test is stopped, or un-
til the ignition switch is turned to the Off position.
(6) With the DRBII scan tool, use the ASD Fuel
System Test to pressurize system and check for
leaks.
MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR
SERVICE
(1) Remove vacuum hose and remove mounting
screws from sensor (Fig. 14). (2) Remove wiring harness and remove sensor.
(3) Reverse the above procedure for installation.
PCM SERVICE
(1) Remove air cleaner duct from PCM.
(2) Remove battery.
(3) Remove PCM mounting screws (Fig. 15).
(4) Remove 60 way wiring connector from module
and remove module. (5) Reverse the above procedure for installation.
METHANOL CONCENTRATION SENSOR
Refer to the Fuel Delivery section of this group for
methanol concentration sensor service.
HEATED OXYGEN SENSOR (O2SENSOR)
The oxygen sensor is installed in the exhaust man-
ifold (Fig. 16).
CAUTION: Do not pull on the oxygen sensor wires
when disconnecting the electrical connector.
WARNING: THE EXHAUST MANIFOLD MAY BE EX-
TREMELY HOT. USE CARE WHEN SERVICING THE
OXYGEN SENSOR.
Fig. 13 Fuel Pressure Regulator Removal/InstallationFig. 14 Manifold Absolute Pressure Sensor
Fig. 15 PCM Removal/Installation
14 - 82 FUEL SYSTEMS Ä

(1) Disconnect oxygen sensor electrical connector.
(2) Remove sensor using Tool C-4907 (Fig. 17).
Slightly tightening the sensor can ease removal. When the sensor is removed, the exhaust manifold
threads must be cleaned with an 18 mm X 1.5 + 6E tap.
If using original sensor, coat the threads with Loctite
771-64 anti-seize compound or equivalent. New sen-
sors are packaged with compound on the threads and
do not require additional compound. The sensor must
be tightened to 28 N Im (20 ft. lbs.) torque.
2.2L TURBO III MULTI-PORT FUEL INJECTIONÐSYSTEM OPERATION
INDEX
page page
Air Conditioning Clutch RelayÐPCM Output .... 89
Air Conditioning Switch SenseÐPCM Input ..... 85
Auto Shutdown (ASD) Relay and Fuel Pump RelayÐPCM Output ..................... 89
Barometric Read SolenoidÐPCM Output ....... 90
Battery VoltageÐPCM Input ................ 85
Brake SwitchÐPCM Input .................. 85
Camshaft Position SensorÐPCM Input ........ 85
Canister Purge SolenoidÐPCM Output ........ 90
CCD Bus .............................. 84
Charge Air Temperature SensorÐPCM Input . . . 86
Crankshaft Position SensorÐPCM Input ....... 87
Data Link ConnectorÐPCM Output ........... 91
Engine Coolant Temperature SensorÐPCM Input . 86
Fuel InjectorÐPCM Output ................. 91
Fuel Injectors and Fuel Rail Assembly ......... 94
Fuel Pressure Regulator ................... 94
Fuel Supply Circuit ....................... 94
General Information ....................... 83
Generator FieldÐPCM Output ............... 89 Heated Oxygen Sensor (O
2Sensor)ÐPCM Input . 88
Idle Air Control MotorÐPCM Output .......... 90
Ignition CoilÐPCM Output .................. 91
Knock SensorÐPCM Input ................. 87
Malfunction Indicator Lamp (Check Engine)ÐPCM Output ............................... 90
Manifold Absolute Pressure (Map) SensorÐPCM Input ................................ 87
Modes of Operation ....................... 92
Powertrain Control Module ................. 84
Radiator Fan RelayÐPCM Output ............ 91
Speed Control SolenoidsÐPCM Output ........ 91
Speed ControlÐPCM Input ................. 88
System Diagnosis ........................ 84
TachometerÐPCM Output .................. 91
Throttle Body ............................ 94
Throttle Position Sensor (TPS)ÐPCM Input ..... 88
Vehicle Speed SensorÐPCM Input ........... 89
Wastegate Control SolenoidÐPCM Output ..... 91
GENERAL INFORMATION
The turbocharged multi-port electronic fuel injec-
tion system combines an electronic fuel and spark
advance control system with a turbocharged intake
system (Fig. 1). The fuel injection system is con-
trolled by the powertrain control module (PCM). The PCM regulates ignition timing, air-fuel ratio,
emission control devices, cooling fan, charging sys-
tem, speed control, turbocharger wastegate and idle
speed. The PCM adapts its requirement to meet
changing operating conditions. Various sensors provide the inputs necessary for
the PCM to correctly regulate fuel flow at the fuel
injector. These include the manifold absolute pres-
sure, throttle position, oxygen sensor, coolant tem-
perature, detonation, and vehicle speed sensors. In
addition to the sensors, the air conditioning clutch
switch and various relays provide important informa-
tion and system control. The outputs include the auto
shutdown relay and fuel pump relay. All inputs to the PCM are converted into signals.
Based on these inputs the PCM adjusts air-fuel ratio,
ignition timing, turbocharger wastegate and other
Fig. 16 Heated Oxygen Sensor
Fig. 17 Oxygen Sensor Socket
Ä FUEL SYSTEMS 14 - 83

controlled outputs. The PCM adjusts the air-fuel ra-
tio by changing injector pulse width. Injector pulse
width is the time an injector is energized.
SYSTEM DIAGNOSIS
The PCM tests many of its own input and output
circuits. If a fault is found in a major system, the in-
formation is stored in memory. Technicians can dis-
play fault information through the malfunction
indicator lamp (instrument panel Check Engine
lamp). Also, the technician can read fault informa-
tion by connecting the DRBII scan tool to the data
link connector. For diagnostic trouble code informa-
tion, refer to the 2.2L Turbo III Multi-Port Fuel In-
jectionÐOn-Board Diagnostics section of this group.
CCD BUS
Various modules exchange information through a
communications port called the CCD Bus. The pow-
ertrain control module (PCM) transmits vehicle load
data on the CCD Bus.
POWERTRAIN CONTROL MODULE
The powertrain control module (PCM) is a digital
computer containing a microprocessor (Fig. 2). The
PCM receives input signals from various switches
and sensors that are referred to as PCM Inputs.
Based on these inputs, the PCM adjusts various en-
gine and vehicle operations through devices that are referred to as PCM Outputs.
PCM Inputs:
² Air Conditioning Controls
² Battery Voltage
² Brake Switch
² Camshaft Position Sensor
² Crankshaft Position Sensor
² Charge Air Temperature Sensor
² Engine Coolant Temperature Sensor
² Knock Sensor
Fig. 1 Electronic Fuel Injection Components
Fig. 2 PCM
14 - 84 FUEL SYSTEMS Ä

² Manifold Absolute Pressure (MAP) Sensor
² Oxygen Sensor
² SCI Receive
² Speed Control System Controls
² Throttle Position Sensor
² Vehicle Speed Sensor
PCM Outputs:
² Air Conditioning Clutch Relay
² Generator Field
² Idle Air Control Motor
² Auto Shutdown (ASD) Relay
² Barometric Read Solenoid
² Canister Purge Solenoid
² Malfunction Indicator Lamp (Check Engine Lamp)
² Data Link Connector
² Fuel Injectors
² Ignition Coil
² Radiator Fan Relay
² Speed Control Solenoids
² Tachometer Output
² Wastegate Solenoid
Based on inputs it receives, the PCM adjusts fuel
injector pulse width, idle speed, ignition spark ad-
vance, ignition coil dwell and canister purge opera-
tion. The PCM regulates operation of the cooling fan,
A/C and speed control systems. The PCM changes
generator charge rate by adjusting the generator
field. The PCM adjusts injector pulse width (air-fuel ra-
tio) based on the following inputs.
² battery voltage
² engine coolant temperature
² exhaust gas content
² engine speed (crankshaft position sensor)
² manifold absolute pressure
² throttle position
The PCM adjusts ignition timing based on the fol-
lowing inputs.
² engine coolant temperature
² knock sensor
² engine speed (crankshaft position sensor)
² manifold absolute pressure
² throttle position
The Automatic Shut Down (ASD) and Fuel Pump
relays are mounted externally, but turned on and off
by the PCM through the same circuit. The camshaft position sensor and crankshaft posi-
tion sensor signals are sent to the PCM. If the PCM
does not receive both signals within approximately
one second of engine cranking, it deactivates the
ASD relay and fuel pump relay. When these relays
are deactivated, power is shut off to the fuel injector,
ignition coil, oxygen sensor heating element and fuel
pump. The PCM contains a voltage converter that
changes battery voltage to a regulated 8.0 volts. The
8.0 volts power the camshaft position sensor, crank- shaft position sensor and vehicle speed sensor. The
PCM also provides a 5.0 volts supply for the coolant
temperature sensor, manifold absolute pressure sen-
sor and throttle position sensor.
AIR CONDITIONING SWITCH SENSEÐPCM INPUT
When the air conditioning or defrost switch is put
in the ON position and the low pressure and high
pressure switches are closed, the PCM receives an in-
put for air conditioning. After receiving this input,
the PCM activates the A/C compressor clutch by
grounding the A/C clutch relay. The PCM also ad-
justs idle speed to a scheduled RPM to compensate
for increased engine load.
BATTERY VOLTAGEÐPCM INPUT
The PCM monitors the battery voltage input to de-
termine fuel injector pulse width and generator field
control. If battery voltage is low the PCM will in-
crease injector pulse width (period of time that the
injector is energized).
BRAKE SWITCHÐPCM INPUT
When the brake switch is activated, the PCM re-
ceives an input indicating that the brakes are being
applied. After receiving this input, the PCM vents
the speed control servo. Venting the servo turns the
speed control system off. The brake switch is
mounted on the brake pedal support bracket.
CAMSHAFT POSITION SENSORÐPCM INPUT
Fuel injection synchronization and cylinder identi-
fication are provided through the camshaft position
sensor (Fig. 3). The sensor generates pulses. The
pulse are the input sent to the PCM. The PCM inter-
prets the camshaft position sensor input along with
the crankshaft position sensor input to determine
crankshaft position. The PCM uses crankshaft posi-
tion sensor input to determine injector sequence and
ignition timing.
Fig. 3 Camshaft Sensor
Ä FUEL SYSTEMS 14 - 85

The camshaft position sensor senses when a notch in
the camshaft gear passes beneath it (Fig. 4). When
metal aligns with the sensor, voltage goes low (less
than 0.3 volts). When a notch aligns with the sensor,
voltage spikes high (5.0 volts). As a group of notches
pass under the sensor, the voltage switches from low
(metal) to high (notch) then back to low. The number of
notches determine the amount of pulses. If available,
an oscilloscope can display the square wave patterns of
each timing events. Top dead center (TDC) does not occur when notches
on the camshaft sprocket pass below the cylinder. TDC
occurs after the camshaft pulse (or pulses) and after
the 4 crankshaft pulses associated with the particular
cylinder.
The camshaft position sensor is mounted on the top
of the cylinder head (Fig. 5). The bottom of the sensor
is positioned above the camshaft sprocket. The dis-
tance between the bottom of sensor and the
camshaft sprocket is critical to the operation of
the system. When servicing the camshaft posi-
tion sensor, refer to the 2.2L Turbo III Multi-Port
Fuel InjectionÐService Procedures section in
this Group.
CHARGE AIR TEMPERATURE SENSORÐPCM IN-
PUT
The charge air temperature sensor is mounted to
intake manifold. The sensor measures the temperature
of the air-fuel mixture (Fig. 6). This information is used
by the PCM to modify air/fuel mixture and turbo-
charger boost level.
ENGINE COOLANT TEMPERATURE SENSORÐPCM
INPUT
The coolant temperature sensor is a variable resis-
tor with a range of -40ÉC to 128ÉF (-40ÉF to 265ÉF).
The sensor is installed into the thermostat housing
(Fig. 7). The PCM supplies 5.0 volts to the coolant temper-
ature sensor. The sensor provides an input voltage to
the PCM. The PCM determines engine operating
temperature from this input. As coolant temperature
varies, the sensor resistance changes resulting in a
different input voltage to the PCM. Based on the coolant sensor and charge air temper-
ature sensor inputs the PCM changes certain operat-
ing schedules until the engine reaches operating
temperature. While the engine warms up, the PCM
demands slightly richer air-fuel mixtures, lower
boost levels, revised spark advance and higher idle
speeds.
Fig. 5 Camshaft Position Sensor Location
Fig. 6 Charge Air Temperature Sensor
Fig. 4 Camshaft Gear
14 - 86 FUEL SYSTEMS Ä

CRANKSHAFT POSITION SENSORÐPCM INPUT
The crankshaft position sensor (Fig. 8) senses slots
cut into the flywheel. There ar e a 2 sets of slots.
Each set contains 4 slots, for a total of 8 slots (Fig.
9). Basic timing is set by the position of the last slot
in each group. Once the PCM senses the last slot, it
determines crankshaft position (which piston will
next be at TDC) from the camshaft position sensor
input. The 4 pulses generated by the crankshaft po-
sition sensor represent the 69É, 49É, 29É, and 9É BTDC
marks. It may take the PCM one engine revolution
to determine crankshaft position. The Turbo III en-
gine uses a fixed ignition system. Base timing is not
adjustable.
The PCM uses the crankshaft position sensor input
to determine injector sequence and ignition timing.
Once crankshaft position has been determined, the
PCM begins energizing the injectors in sequence. The crankshaft position sensor is located in the
transaxle housing, below the throttle body (Fig. 10).
The bottom of the sensor is positioned next to the
drive plate. The distance between the bottom of sensor and the drive plate is critical to the oper-
ation of the system. When servicing the crank-
shaft position sensor, refer to the 2.2L Turbo III
Multi-Port Fuel InjectionÐService Procedures
section in this Group.
KNOCK SENSORÐPCM INPUT
The knock sensor generates a signal when spark
knock occurs in the combustion chambers. The sensor
can detect detonation in the cylinders. The sensor
provides information used by the PCM to modify
spark advance and boost schedules in order to elimi-
nate detonation. The knock sensor is installed into the engine, be-
hind the PCV breather/separator (Fig. 11).
MANIFOLD ABSOLUTE PRESSURE (MAP)
SENSORÐPCM INPUT
The PCM supplies 5 volts to the MAP sensor. The
Map sensor converts intake manifold pressure into
voltage. The PCM monitors the MAP sensor output
voltage. As vacuum increases, MAP sensor voltage
decreases proportionately. Also, as vacuum decreases,
MAP sensor voltage increases proportionately.
Fig. 7 Coolant Temperature Sensor
Fig. 8 Crankshaft Position Sensor
Fig. 9 Timing Slots
Fig. 10 Crankshaft Position Sensor Location
Ä FUEL SYSTEMS 14 - 87

During cranking, before the engine starts running,
the PCM determines atmospheric air pressure from
the MAP sensor voltage. While the engine operates,
the PCM determines intake manifold pressure and
barometric pressure from the MAP sensor voltage.
Based on MAP sensor voltage and inputs from other
sensors, the PCM adjusts spark advance, air/fuel
mixture and controls the turbocharger wastegate. The MAP sensor (Fig. 12) mounts underhood on
the right side of the engine compartment. The sensor
connects electrically to the PCM.
HEATED OXYGEN SENSOR (O2SENSOR)ÐPCM
INPUT
The O2sensor is located in the turbocharger outlet
and provides an input voltage to the PCM (Fig. 13).
The input tells the PCM the oxygen content of the
exhaust gas. The PCM uses this information to fine
tune the air-fuel ratio by adjusting injector pulse
width. The O
2sensor produces voltages from 0 to 1 volt,
depending upon the oxygen content of the exhaust
gas in the exhaust manifold. When a large amount of oxygen is present (caused by a lean air-fuel mixture),
the sensor produces a low voltage. When there is a
lesser amount present (rich air-fuel mixture) it pro-
duces a higher voltage. By monitoring the oxygen
content and converting it to electrical voltage, the
sensor acts as a rich-lean switch. The oxygen sensor is equipped with a heating ele-
ment that keeps the sensor at proper operating tem-
perature during all operating modes. Maintaining
correct sensor temperature at all times allows the
system to enter into closed loop operation sooner.
Also, it allows the system to remain in closed loop
operation during periods of extended idle. In Closed Loop operation the PCM monitors the O
2
sensor input (along with other inputs) and adjusts
the injector pulse width accordingly. During Open
Loop operation the PCM ignores the O
2sensor input.
The PCM adjusts injector pulse width based on pre-
programmed (fixed) values and inputs from other
sensors.
SPEED CONTROLÐPCM INPUT
The speed control system provides four separate
voltages (inputs) to the PCM. The voltages corre-
spond to the On/Off, Set, and Resume. The speed control ON voltage informs the PCM
that the speed control system has been activated.
The speed control SET voltage informs the PCM that
a fixed vehicle speed has been selected. The speed
control RESUME voltage indicates the previous fixed
speed is requested. The speed control OFF voltage
tells the PCM that the speed control system has de-
activated. Refer to Group 8H for further speed con-
trol information.
THROTTLE POSITION SENSOR (TPS)ÐPCM INPUT
The Throttle Position Sensor (TPS) is mounted on
the throttle body and connected to the throttle blade
shaft (Fig. 14). The TPS is a variable resistor that
provides the PCM with an input signal (voltage) rep-
Fig. 11 Knock Sensor
Fig. 12 MAP Sensor
Fig. 13 Heated Oxygen Sensor
14 - 88 FUEL SYSTEMS Ä

resenting throttle blade position. As the position of
the throttle blade changes, the resistance of the TPS
changes. The PCM supplies approximately 5 volts to the
TPS. The TPS output voltage (input signal to the
PCM) represents the throttle blade position. The TPS
output voltage to the PCM varies from approxi-
mately 0.5 volt at minimum throttle opening (idle) to
4 volts at wide open throttle. Along with inputs from
other sensors, the PCM uses the TPS input to deter-
mine current engine operating conditions and adjust
fuel injector pulse width and ignition timing.
VEHICLE SPEED SENSORÐPCM INPUT
The vehicle speed sensor (Fig. 15) is located on the
transaxle extension housing. The sensor input is
used by the PCM to determine vehicle speed and dis-
tance traveled.
The speed sensor generates 8 pulses per sensor rev-
olution. These signals, along with a closed throttle
signal from the TPS, determine if a closed throttle
deceleration or normal idle condition (vehicle
stopped) exists. Under deceleration conditions, the
PCM adjusts the idle air control motor to maintain a desired MAP value. Under idle conditions, the PCM
adjusts the idle air control motor to maintain desired
engine speed.
AIR CONDITIONING CLUTCH RELAYÐPCM
OUTPUT
The PCM operates the air conditioning clutch relay
ground circuit. The radiator fan relay supplies bat-
tery power to the solenoid side of the A/C clutch re-
lay. The air conditioning clutch relay will not
energize unless the radiator fan relay energizes. The
PCM energizes the radiator fan relay when the air
conditioning or defrost switch is put in the ON posi-
tion and the low pressure and high pressure switches
close. When the PCM senses wide open throttle
through the throttle position sensor, or low engine
RPM it will de-energize the A/C clutch relay, open
it's contacts and prevent air conditioning clutch en-
gagement. On AG Body vehicles, the relay is located in the
power distribution center (Fig. 16).
GENERATOR FIELDÐPCM OUTPUT
The PCM regulates the charging system voltage
within a range of 12.9 to 15.0 volts. Refer to Group
8A for charging system information.
AUTO SHUTDOWN (ASD) RELAY AND FUEL PUMP
RELAYÐPCM OUTPUT
The PCM operates the auto shutdown (ASD) relay
and fuel pump relay through one ground path. The
PCM operates the relays by switching the ground
path on and off. Both relays turn on and off at the
same time. The ASD relay connects battery voltage to the fuel
injector and ignition coil. The fuel pump relay con-
nects battery voltage to the fuel pump and oxygen
sensor heating element. The PCM turns the ground path off when the igni-
tion switch is in the Off position. Both relays are off.
When the ignition switch is in the On or Crank po-
Fig. 14 Throttle Position Sensor and Idle Air Control Motor
Fig. 15 Vehicle Speed Sensor
Fig. 16 Power Distribution CenterÐAG Body
Ä FUEL SYSTEMS 14 - 89

sition, the PCM monitors the crankshaft position and
camshaft position sensor signals to determine engine
speed and ignition timing (coil dwell). If the PCM
does not receive the crankshaft position sensor and
camshaft position sensor signals when the ignition
switch is in the Run position, it de-energizes both re-
lays. When the relays are de-energized, battery volt-
age is not supplied to the fuel injector, ignition coil,
fuel pump and oxygen sensor heating element. The ASD relay and fuel pump relay are located in
the power distribution center (Fig. 16).
IDLE AIR CONTROL MOTORÐPCM OUTPUT
The idle air control motor is mounted on the throt-
tle body (Fig. 14). The PCM operates the motor. The
PCM adjusts engine idle speed through the idle air
control motor to compensate for engine load or ambi-
ent conditions. The throttle body has an air bypass passage that
provides air for the engine at idle (the throttle blade
is closed). The idle air control motor pintle protrudes
into the air bypass passage and regulates air flow
through it. The PCM adjusts engine idle speed by moving the
idle air control motor pintle in and out of the bypass
passage. The adjustments are based on inputs the
PCM receives. The inputs are from the throttle posi-
tion sensor, camshaft position sensor, crankshaft po-
sition sensor, coolant temperature sensor, and
various switch operations (brake and air condition-
ing). Deceleration die out is also prevented by in-
creasing airflow when the throttle is closed quickly
after a driving (speed) condition.
BAROMETRIC READ SOLENOIDÐPCM OUTPUT
The barometric pressure read solenoid is spliced
into the manifold absolute pressure (MAP) sensor
vacuum hose (Fig. 12). The barometric read solenoid
switches the pressure supply to the MAP sensor from
either barometric pressure (atmospheric) or manifold
vacuum. The PCM operates the solenoid. Atmospheric pressure is periodically supplied to
the MAP sensor to measure barometric pressure.
This occurs at closed throttle, once per throttle clo-
sure but no more often than once every 3 minutes
and within a specified RPM band. Barometric infor-
mation is used primarily for boost control and start
fuel enrichment at various altitudes.
CANISTER PURGE SOLENOIDÐPCM OUTPUT
Vacuum for the Evaporative Canister is controlled
by the Canister Purge Solenoid (Fig. 17). The sole-
noid is controlled by the PCM. The PCM operates the solenoid by switching the
ground circuit on and off. When grounded, the sole-
noid energizes and prevents vacuum from reaching
the evaporative canister. When not energized the so-
lenoid allows vacuum to flow to the canister. During warm-up and for a specified time period after
hot starts the PCM grounds the purge solenoid.
Vacuum does not operate the evaporative canister
valve. The PCM removes the ground to the solenoid when
the engine reaches a specified temperature and the
time delay interval has occurred. When the solenoid is
de-energized, vacuum flows to the canister purge
valve. Vapors are purged from the canister and flow to
the throttle body. The purge solenoid will also be energized during
certain idle conditions, in order to update the fuel
delivery calibration.
MALFUNCTION INDICATOR LAMP (CHECK
ENGINE)ÐPCM OUTPUT
The malfunction indicator lamp (instrument panel
Check Engine lamp) comes on each time the ignition
key is turned ON and stays on for 3 seconds as a bulb
test. The malfunction indicator lamp warns the opera-
tor that the PCM has entered a Limp-in mode. During
Limp-in-Mode, the PCM attempts to keep the system
operational. The malfunction indicator lamp signals
the need for immediate service. In limp-in mode, the
PCM compensates for the failure of certain components
that send incorrect signals. The PCM substitutes for
the incorrect signals with inputs from other sensors. Signals that can trigger the malfunction indi-
cator lamp (Check Engine Lamp).
² Engine Coolant Temperature Sensor
² Manifold Absolute Pressure Sensor
² Throttle Position Sensor
² Battery Voltage Input
² An Emissions Related System
² Charging system
The malfunction indicator lamp can also be used to
display diagnostic trouble codes. Cycle the ignition
switch on, off, on, off, on, within five seconds and any
Fig. 17 EVAP Canister Purge Solenoid and Waste- gate Control Solenoid
14 - 90 FUEL SYSTEMS Ä