engine CHEVROLET DYNASTY 1993 Service Manual

THROTTLE BODY MINIMUM AIR FLOW CHECK
PROCEDURE
(1) Warm engine in Park or neutral until the cooling
fan has cycled on and off at least once. (2) Hook-up timing check device and Tachometer.
(3) Disconnect the coolant temperature sensor and
set basic timing to 12É BTDC 62É BTDC.
(4) Shut off engine. Connect harness connector to
coolant temperature sensor. (5) Disconnect the PCV valve hose from the nipple
on the intake manifold. (6) Attach Air Metering Fitting #6457 (0.125 in.
orifice) to the intake manifold PCV nipple (Fig. 2).
(7) Connect DRBII scan tool to the data link connec-
tor. The connector is located next to the powertrain
control module (PCM) (Fig. 1). (8) Restart engine. Allow engine to idle for at least
one minute. (9) Using the DRBII scan tool, access Min. Airflow
Idle Spd. The following will then occur:
² idle air control motor fully closes ²
Idle spark advance becomes fixed
² The DRBII scan tool displays engine RPM
(10) Check idle RPM with tachometer, if idle RPM is
within the specifications then the throttle body mini-
mum airflow is set correctly.
If the idle RPM is not within specification, replace
the throttle body. (11) Shut off engine.
(12) Remove Air Metering Fitting #6457 from the
intake manifold PCV nipple. Reinstall the PCV valve
hose. (13) Remove DRBII scan tool.
(14) Disconnect timing light and tachometer.
IGNITION TIMING PROCEDURE
Refer to Group 8D Ignition System.
POWERTRAIN CONTROL MODULE 60-WAY CON-
NECTOR
Check the powertrain control module (PCM) 60-way
connector for the following.
² Spread terminals
² Stretched or pulled out wires
² Undertightened or overtightened 60 way connector
Tighten the PCM connector to 4 N Im (35 in. lbs.)
torque. When checking terminal pin outs, refer to the
Powertrain Control Module 60-Way Connector Dia-
gram for circuit wire colors and cavity numbers.
Fig. 2 Checking Minimum Air Flow Using Special Tool 6457
IDLE SPECIFICATIONS
Ä FUEL SYSTEMS 14 - 73

(3) Remove idle air control motor mounting screws.
(4) Remove idle air control motor from throttle
body (make certain that the O-ring is on motor).
INSTALLATION
(1) New idle air control motors have a new O-ring
installed on them. If pintle measures more than 1
inch (25 mm) it must be retracted. Use the IDLE
AIR CONTROL MOTOR OPEN/CLOSE mode of the
DRBII scan tool (battery must be reconnected for this
operation). (2) Carefully place idle air control motor into
throttle body. (3) Install 2 mounting screws. Tighten screws to 2
N Im (17 in. lbs.) torque.
(4) Connect harness connector to motor.
(5) Connect negative cable to battery.
THROTTLE BODY REMOVAL
(1) Disconnect negative cable from battery.
(2) Remove clamp from air hose. Remove hose (Fig.
1). (3) Remove accelerator cable.
(4) Disconnect idle air control motor and throttle
position sensor (TPS) electrical connectors. (5) Remove throttle body mounting nuts.
(6) Remove throttle body and gasket.
(7) Reverse the above procedures for installation.
FUEL INJECTOR RAIL ASSEMBLY
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 the fuel injector harness connector
from the engine harness (Fig. 6).
(4) Remove the quick connect fittings from the
chassis fuel tubes. Refer to Quick Connect Fittings in
the Fuel Delivery section of this group. (5) Disconnect the vacuum hose from the top of the
intake manifold (Fig. 6). (6) Disconnect vacuum hose from the pressure reg-
ulator (Fig. 6). (7) Remove screw from the fuel tube clamp (Fig.
6). (8) Remove fuel rail mounting screws.
(9) Pull up on the injector rail. The injectors will
pull straight out of the ports. Do not damage the in-
jector O-rings. (10) Remove fuel rail assembly from vehicle. Do
not remove fuel injectors until fuel rail assembly has
been completely removed from vehicle. (11) Plug or cover intake manifold injector ports to
prevent dirt from entering the openings (Fig. 7).
INSTALLATION
WARNING: FUEL RAILS, INJECTORS AND PRES-
SURE REGULATORS 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) Ensure injectors are seated into the receiver
cup on the fuel rail with the lock ring in place. (2) Attach harness connectors to injectors. Fasten
the harness into wiring clips.
Fig. 5 Servicing Idle Air Control Motor
Fig. 6 Injector Harness and Engine Harness Connection
Ä FUEL SYSTEMS 14 - 79

(3) Ensure the injector holes are clean and all plugs
have been removed. (4) Lubricate the injector O-rings with a drop of
clean engine oil to ease installation. (5) Install the injector assembly into their holes.
Install mounting screws. Fuel rail assembly must be
drawn into the intake manifold evenly making sure
each injector enters its own hole. Once all injectors are
seated, tighten bolts to 23 N Im (200 in. lbs) torque.
(6) Connect vacuum hose to fuel pressure regulator.
(7) Close fuel tube clip around fuel tubes and install
fastener. (8) Lubricate the ends of the chassis fuel tubes with
a light coating of clean 30 weight engine oil. Connect
fuel supply and return hoses to chassis fuel tube
assembly. Pull back on the quick connect fittings to
ensure complete insertion. Refer to Quick Connect
Fittings in the Fuel Delivery section of this group. (9) Connect vacuum hose intake manifold nipple.
(10) 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 until the
ignition switch is turned to the Off position.
(11) With the DRBII scan tool, use the ASD Fuel
System Test to pressurize system and check for leaks.
FUEL INJECTOR
The fuel rail must be removed to service the injec-
tors. Refer to Fuel Injector Rail Assembly in this
section.
REMOVAL
WARNING: RELEASE FUEL SYSTEM PRESSURE BE-
FORE 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.
(1) Disconnect electrical connector from injector
(Fig. 8).
(2) Position fuel rail assembly so that the fuel injec-
tors are easily accessible (Fig. 9). (3) Remove injector lock ring from fuel rail and
injector. Pull injector straight out of fuel rail receiver
cup. (4) Check injector O-ring for damage. Replace dam-
aged O-rings. If injector is reused, install a protective
cap on the injector tip to prevent damage. (5) Repeat steps for remaining injectors.
INSTALLATION
WARNING: FUEL INJECTORS AND INJECTOR
O-RINGS DESIGNED FOR GASOLINE ONLY VE-
HICLES CANNOT BE USED ON FLEXIBLE FUEL AA-
BODY VEHICLES. WHEN SERVICING THE FUEL SYS-
TEM OF A FLEXIBLE FUEL VEHICLE, ONLY USE
ORIGINAL EQUIPMENT OR EQUIVALENT REPLACE-
MENT COMPONENTS.
Fig. 7 Fuel Injector Ports
Fig. 8 Servicing Fuel Injectors
14 - 80 FUEL SYSTEMS Ä

(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

(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