sensor CHEVROLET DYNASTY 1993 Service Manual

SYSTEM TESTS
Apply parking brake and/or block wheels be-
fore performing idle check or adjustment, or any
engine running tests.
OBTAINING DIAGNOSTIC TROUBLE CODES
(1) Connect DRBII scan tool to the data link connec-
tor (Fig. 1). (2) Start the engine if possible, cycle the trans mis-
sion selector and the A/Cswitch if applicable. Shut off
the engine. (3) Turn the ignition switch on, access Read Fault
Screen. Record all the fault messages shown on the
DRBII scan tool. Observe the malfunction indicator
lamp (check engine lamp on the instrument panel). The
lamp should light for 2 seconds then go out (bulb
check). Diagnostic trouble code erasure: access erase
diagnostic trouble code data.
STATE DISPLAY TEST MODE
The switch inputs used by the powertrain control
module (PCM) have only two recognized states, HIGH
and LOW. For this reason, the PCM cannot recognize
the difference between a selected switch position ver-
sus an open circuit, a short circuit, or a defective
switch. If the display changes, assume the entire
switch circuit to the PCM is functional. From the state
display screen access either State Display Inputs and
Outputs or State Display Sensors.
STATE DISPLAY INPUTS AND OUTPUTS
Connect the DRBII scan tool to the vehicle and access
the State Display screen. Then access Inputs and
Outputs. The following is a list of the engine control
system functions accessible through the Inputs and
Outputs screen. Speed Control Resume
Brake Switch
Speed Control On/Off
Speed Control Set
A/C Switch Sense
S/C Vent Solenoid S/C Vacuum Solenoid
A/C Clutch Relay
Baro Read Solenoid
Wastegate Solenoid
Auto Shutdown Relay
Radiator Fan Relay
Purge Solenoid
Malfunction Indicator Lamp (Check Engine Lamp)
STATE DISPLAY SENSORS
Connect the DRBII scan tool to the vehicle and ac-
cess the State Display screen. Then access Sensor
Display. The following is a list of the engine control
system functions accessible through the Sensor Dis-
play screen. Oxygen Sensor Signal
Coolant Temperature
Coolant Temp Sensor
Throttle Position
Minimum Throttle
Knock Sensor Signal
Battery Voltage
MAP Sensor Reading
Idle Air Control Motor Position
Adaptive Fuel Factor
Barometric Pressure
Min Airflow Idle Spd (speed)
Engine Speed
DIS Sensor Status
Fault #1 Key-On Info
Module Spark Advance
Cyl 1 Knock Retard
Cyl 2 Knock Retard
Cyl 3 Knock Retard
Cyl 4 Knock Retard
Boost Pressure Goal
Charge Temperature
Charge Temp Sensor
Speed Control Target
Fault #2 Key-on Info
Fault #3 Key-on Info
Speed Control Status
Charging System Goal
Theft Alarm Status
DIAGNOSTIC TROUBLE CODE DESCRIPTION (CON'T)
14 - 104 FUEL SYSTEMS Ä

Wastegate Duty Cycle
Battery Temperature
Map Sensor Voltage
Vehicle Speed
Oxygen Sensor State
Baro Read Update
MAP Gauge Reading
Throttle Opening (percentage)
Total Spark Advance
CIRCUIT ACTUATION TEST MODE
The purpose of the circuit actuation test mode is to
check for the proper operation of output circuits or
devices which the powertrain control module (PCM)
cannot internally recognize. The PCM can attempt to
activate these outputs and allow an observer to ver-
ify proper operation. Most of the tests available in
this mode provide an audible or visual indication of
device operation (click of relay contacts, spray fuel,
etc.). With the exception of an intermittent condition,
if a device functions properly during its test, assume
the device, its associated wiring, and its driver cir-
cuit are in working order.
OBTAINING CIRCUIT ACTUATION TEST
Connect the DRBII scan tool to the vehicle and ac-
cess the Actuators screen. The following is a list of
the engine control system functions accessible
through Actuators screens. Stop All Tests
Ignition Coil #1
Ignition Coil #2
Fuel Injector #1
Fuel Injector #2
Fuel Injector #3
Idle Air Control Motor Open/Close
Radiator Fan Relay
A/C Clutch Relay
Auto Shutdown Relay
Purge Solenoid
S/C Serv Solenoids
Generator Field
Tachometer Output
Wastegate Solenoid
Baro Read Solenoid
All Solenoids/Relays
Speed Control Vent Solenoid
Speed Control Vacuum Solenoid
ASD Fuel System Test
Fuel Injector #4
THROTTLE BODY MINIMUM AIR FLOW CHECK
PROCEDURE
(1) Warm the engine in neutral until the cooling
fan has cycled on and off at least once. (2) Shut off engine.
(3) Hook-up Tachometer.
(4) Disconnect the PCV valve hose from the nipple
on the intake manifold. (5) Attach air metering fitting, special tool 6457
(0.125 inch orifice), to the intake manifold PCV nip-
ple. (6) Disconnect 3/16 inch manifold vacuum purge
line from the top of the throttle body. Cap the 3/16
inch throttle body nipple. (7) Connect DRBII scan tool.
(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 will fully close.
² Idle spark advance will become fixed.
² Engine RPM will be displayed on the DRBII scan
tool. (10) Check idle RPM with tachometer, if idle RPM
is within the below specification then the throttle
body minimum 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 in-
take manifold PCV nipple. Connect the PCV hose to
the nipple. (13) Remove DRBII scan tool.
(14) Disconnect tachometer.
(15) Reconnect purge line to throttle body.
IGNITION TIMING PROCEDURE
Ignition timing cannot be changed or set on the
Turbo III engine. Refer to Group 8D for a description
of the Direct Ignition System (DIS).
60-WAY PCM WIRING CONNECTOR
Refer to the PCM wiring connector diagram (Fig.
2) for information regarding wire colors and cavity
numbers.
IDLE SPECIFICATIONS
Ä FUEL SYSTEMS 14 - 105

2.2L TURBO III MULTI-PORT FUEL INJECTIONÐSERVICE PROCEDURES INDEX
page page
Fuel Injector Rail Assembly ................ 109
Fuel Injectors .......................... 110
Fuel Pressure Regulator .................. 111
Fuel System Pressure Release Procedure ..... 107
Heated Oxygen Sensor (O
2Sensor) ......... 112
Idle Air Control Motor .................... 108
Manifold Absolute Pressure (MAP) Sensor Service .............................. 111 PCM Service
........................... 111
Throttle Body ........................... 107
Throttle Body Removal ................... 108
Throttle Position Sensor (TPS) ............. 107
Wastegate and Canister Purge Solenoid Service . 111
THROTTLE BODY
When servicing throttle body components, always
reassemble components with new O-rings and seals
where applicable (Fig. 1). Never use lubricants on
O-rings or seals, damage may result. If assembly of
component is difficult, use water to aid assembly.
Use care when removing hoses to prevent damage to
hose or hose nipple.
FUEL SYSTEM PRESSURE RELEASE PROCEDURE
CAUTION: The fuel system is under a constant
pressure of approximately 380 kPa (55 psi). Before
servicing the fuel pump, fuel lines, fuel filter, throt-
tle body, or fuel injectors, the fuel system pressure
must be released.
(1) Disconnect negative cable from battery.
(2) Remove fuel filler cap. (3) Remove the protective cap from the fuel pres-
sure test port on the fuel rail (Fig. 2). (4) Place the open end of fuel pressure release
hose, tool number C-4799-1, into an approved gaso-
line container. Connect the other end of hose
C-4799-1 to the fuel pressure test port. Fuel pressure
will bleed off through the hose into the gasoline con-
tainer. Fuel gauge C-4799-A contains hose C-4799-1. (5) Continue fuel system service.THROTTLE POSITION SENSOR (TPS)
REMOVAL
(1) Disconnect the negative cable from the battery.
(2) Disconnect harness connector from throttle po-
sition sensor (Fig. 3). (3) Remove throttle position sensor mounting
screws. (4) Lift throttle position sensor off throttle shaft.
Fig. 1 Throttle Body
Ä FUEL SYSTEMS 14 - 107

INSTALLATION
(1) Install throttle position sensor on throttle shaft.
Install mounting screws. Tighten screws to 2 N Im (17
in. lbs.) torque. (2) Attach harness connector to sensor.
(3) Connect negative cable to negative post of the
battery.
IDLE AIR CONTROL MOTOR
REMOVAL
(1) Disconnect negative cable from battery.
(2) Disconnect harness connector from idle air con-
trol motor (Fig. 4). (3) Remove idle air control motor mounting screws.
(4) Remove the motor from throttle body. Ensure the
O-ring is was removed with the idle air control 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 by using the IDLE
AIR CONTROL MOTOR OPEN/CLOSE mode of the
DRBII scan tool. (2) Carefully place idle air control motor into
throttle body. (3) Install 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.
5). (3) Remove accelerator cable.
(4) Disconnect idle air control motor and throttle
position sensor (TPS) electrical connectors (Fig. 6). (5) Disconnect vacuum hoses from throttle body.
(6) Remove throttle body to intake manifold at-
taching nuts (2). (7) Remove throttle body and gasket.
INSTALLATION
(1) Install throttle body with new gasket.
(2) Install throttle body attaching nuts. Tighten
nuts to 25 N Im (225 in. lbs.) torque.
(3) Connect vacuum hoses to the throttle body.
(4) Attach harness connectors to the throttle posi-
tion sensor (TPS) and the idle air control motor. (5) Install throttle and speed control cables (if ap-
plicable). (6) Install throttle body intake air hose. Tighten
clamp to 4 N Im (30 in. lbs.) torque.
(7) Connect negative cable to battery.
Fig. 4 Idle Air Control MotorFig. 2 Fuel Pressure Test Port
Fig. 3 Throttle Position Sensor
14 - 108 FUEL SYSTEMS Ä

INSTALLATION
(1) Before installing an injector, the rubber O-ring
must be lubricated with a drop of clean engine oil to aid
in installation. (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. 11). (4) Repeat steps for remaining injectors.
(5) Install injector wiring harness to injectors. Place
harness into retaining clips.
FUEL PRESSURE REGULATOR
WARNING: THE 2.2L TURBO III FUEL SYSTEM IS
UNDER A CONSTANT PRESSURE OF APPROXI-
MATELY 380 KPA (55 PSI). PERFORM FUEL PRES-
SURE RELEASE PROCEDURE BEFORE SERVICING
THE FUEL PRESSURE REGULATOR.
REMOVAL
(1) Perform fuel system pressure release procedure.
(2) Disconnect negative cable from battery.
(3) Disconnect vacuum hose from fuel pressure regu-
lator (Fig. 12).
Place a shop towel under fuel pressure regula-
tor to absorb any fuel spillage. (4) Loosen fuel hose clamp and remove fuel return
hose. (5) Remove fuel pressure regulator mounting nuts.
Remove fuel pressure regulator from rail (Fig. 12).
Check O-Ring for damage. If O-Ring is damaged it
must be replaced.
INSTALLATION
(1) Lubricate O-ring with a drop of clean engine oil.
Install O-ring into the receiver cup on fuel rail. (2) Install fuel pressure regulator mounting nuts.
Tighten nuts to 7 N Im (65 in. lbs.) torque. (3) Connect fuel return hose to pressure regulator.
Tighten hose clamp to 1 N Im (10 in. lbs.) torque (Fig.
12). (4) Install vacuum hose on fuel pressure regulator.
(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 the ASD Fuel System
Test to pressurize system and check for leaks.
MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR
SERVICE
(1) Remove vacuum hose from MAP sensor (Fig.
13) (2) Remove MAP sensor mounting screws (Fig. 13).
(3) Remove electrical connector. Remove sensor.
(4) Reverse the above procedure for installation.
WASTEGATE AND CANISTER PURGE SOLENOID
SERVICE
(1) Remove vacuum hoses from sensors (Fig. 14).
(2) Disconnect electrical connector from solenoids
(Fig. 14). (3) Remove solenoid pack mounting nut. Remove
solenoid pack. (4) Depress tab on top of solenoid to be replaced
and slide the solenoid downward out of mounting
bracket. (5) Reverse above procedure to install.
PCM SERVICE
(1) Remove air cleaner duct from PCM.
(2) Remove battery.
(3) Remove PCM mounting screws (Fig. 15).
(4) Disconnect the 60-way wiring connector. Re-
move the PCM. (5) Reverse the above procedure for installation.
Fig. 13 Manifold Absolute Pressure Sensor
Fig. 12 Servicing Fuel Pressure Regulator
Ä FUEL SYSTEMS 14 - 111

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. (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 sensors are packaged with compound on the
threads and do not require additional compound.
Tighten the sensor to 27 N Im (20 ft. lbs.) torque.
Fig. 14 Solenoid Mounting
Fig. 15 PCM
Fig. 16 Heated Oxygen Sensor
Fig. 17 Oxygen Sensor Socket
14 - 112 FUEL SYSTEMS Ä

3.0L MULTI-PORT FUEL INJECTIONÐSYSTEM OPERATION INDEX
page page
Air Conditioning (A/C) Clutch Relay (AA, AG, AJ Body)ÐPCM Output .................... 118
Air Conditioning (A/C) Clutch Relay (AC Body) ÐPCM Output ........................ 118
Air Conditioning Switch Sense (AA, AG, AJ Body)ÐPCM Input ..................... 115
Air Conditioning Switch Sense (AC Body)ÐPCM Input ................................ 115
Auto Shutdown (ASD) Relay and Fuel Pump RelayÐPCM Output .................... 119
Battery VoltageÐPCM Input ............... 115
Brake SwitchÐPCM Input ................. 115
CCD Bus .............................. 113
Data Link ConnectorÐPCM Output .......... 120
Distributor Pick-UpÐPCM Input ............. 115
Duty Cycle Evap Canister Purge Solenoid ÐPCM Output ........................ 119
Engine Coolant Temperature Sensor ÐPCM Input ......................... 115
Fuel InjectorsÐPCM Output ............... 120
Fuel Pressure Regulator .................. 124
Fuel Supply Circuit ...................... 123
General Information ...................... 113 Generator FieldÐPCM Output
.............. 118
Heated Oxygen Sensor (O
2Sensor)
ÐPCM Input ......................... 116
Idle Air Control MotorÐPCM Output ......... 119
Ignition CoilÐPCM Output ................. 121
Malfunction Indicator Lamp (Check Engine Lamp)ÐPCM Output ................... 120
Manifold Absolute Pressure (MAP) Sensor ÐPCM Input ......................... 116
Modes of Operation ...................... 121
Park/Neutral SwitchÐPCM Input ............ 117
Part Throttle Unlock SolenoidÐPCM Output . . . 121
Powertrain Control Module ................. 113
Radiator Fan RelayÐPCM Output ........... 121
Speed Control SolenoidsÐPCM Output ....... 121
Speed ControlÐPCM Input ................ 117
System Diagnosis ....................... 113
TachometerÐPCM Output ................. 121
Throttle Body ........................... 123
Throttle Position Sensor (TPS)ÐPCM Input .... 117
Transaxle Control ModuleÐPCM Output ...... 120
Vehicle Speed and Distance InputÐPCM Input . 118
Vehicle Speed SensorÐPCM Input .......... 118
GENERAL INFORMATION
The 3.0L engine uses a sequential Multi-Port Elec-
tronic Fuel Injection system (Fig. 1). The MPI system
is computer regulated and provides precise air/fuel
ratios for all driving conditions. The MPI system is operated by the powertrain con-
trol module (PCM). The PCM regulates ignition timing, air-fuel ratio,
emission control devices, cooling fan, charging sys-
tem, idle speed and speed control. Various sensors
provide the inputs necessary for the PCM to correctly
operate these systems. In addition to the sensors,
various switches also provide inputs to the PCM. All inputs to the PCM are converted into signals.
The PCM can adapt its programming to meet chang-
ing operating conditions. Fuel is injected into the intake port above the in-
take valve in precise metered amounts through elec-
trically operated injectors. The PCM fires the
injectors in a specific sequence. The PCM maintains
an air fuel ratio of 14.7 parts air to 1 part fuel by
constantly adjusting injector pulse width. Injector
pulse width is the length of time the injector is ener-
gized. The PCM adjusts injector pulse width by opening
and closing the ground path to the injector. Engine
RPM (speed) and manifold absolute pressure (air
density) are the primary inputs that determine injec-
tor pulse width.
SYSTEM DIAGNOSIS
The powertrain control module (PCM) tests many
of its own input and output circuits. If a fault is
found in a major system, the information is stored in
memory. Technicians can display fault information
through the malfunction indicator lamp (instrument
panel Check Engine lamp) or by connecting the
DRBII scan tool. For diagnostic trouble code informa-
tion, refer to the 3.0 Multi-Port Fuel InjectionÐOn-
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 the malfunc-
tion indicator (instrument panel check engine lamp)
On/Off signal, engine RPM and 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 referred
to as PCM Outputs. PCM Inputs:
² Air Conditioning Controls
² Battery Voltage
² Brake Switch
Ä FUEL SYSTEMS 14 - 113

² Engine Coolant Temperature Sensor
² Distributor Pick-up
² Manifold Absolute Pressure (MAP) Sensor
² Oxygen Sensor
² SCI Receive
² Speed Control System Controls
² Throttle Position Sensor
² Park/Neutral Switch (automatic transaxle)
² Vehicle Speed Sensor
PCM Outputs:
² Air Conditioning Clutch Relay ²
Generator Field
² Idle Air Control Motor
² Auto Shutdown (ASD) and Fuel Pump Relays
² Canister Purge Solenoid
² Malfunction Indicator Lamp (Check Engine Lamp)
² Data Link Connector
² Electric EGR Transducer (EET)
² Fuel Injectors
² Ignition Coil
² Torque Converter Clutch Solenoid
² Radiator Fan Relay
² Speed Control Solenoids
² Tachometer Output
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 the cooling fan, air
conditioning and speed control systems. The PCM
changes generator charge rate by adjusting the gen-
erator 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 (distributor pick-up)
² manifold absolute pressure
² throttle position
Fig. 1 Multi-Port Fuel Injection Components
Fig. 2 PCM
14 - 114 FUEL SYSTEMS Ä

The PCM adjusts ignition timing based on the fol-
lowing inputs.
² engine coolant temperature
² engine speed (distributor pick-up)
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 distributor pick-up signal is sent to the PCM.
If the PCM does not receive a distributor signal
within approximately one second of engine cranking,
the ASD relay and fuel pump relay are deactivated.
When these relays are deactivated, power is shut off
to the fuel injector, ignition coil, oxygen sensor heat-
ing 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 distributor pick-up and vehicle
speed sensor. The PCM also provides a 5.0 volts sup-
ply for the coolant temperature sensor, manifold ab-
solute pressure sensor and throttle position sensor.
AIR CONDITIONING SWITCH SENSE (AA, AG, AJ
BODY)ÐPCM INPUT
When the air conditioning or defrost switch is in
the ON position and the low pressure and high pres-
sure switches are closed, the PCM receives an input
for air conditioning. After receiving this input, the
PCM activates the A/C compressor clutch by ground-
ing the A/C clutch relay. The PCM also adjusts idle
speed to a scheduled RPM to compensate for in-
creased engine load.
AIR CONDITIONING SWITCH SENSE (AC
BODY)ÐPCM INPUT
When the air conditioning or defrost switch is in
the ON position and the low pressure, high pressure
and ambient temperature switches are closed, the
PCM receives an input for air conditioning. After re-
ceiving this input, the PCM activates the A/C com-
pressor clutch by grounding the A/C clutch relay.
The PCM also adjusts 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.
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 main-
tains idle speed to a scheduled RPM through the idle
air control motor. The brake switch is mounted on
the brake pedal support bracket.
ENGINE COOLANT TEMPERATURE SENSORÐPCM
INPUT
The coolant temperature sensor is a variable resis-
tor with a range of -40É to 265É. The sensor is in-
stalled next to the thermostat housing. The PCM supplies 5.0 volts to the coolant temper-
ature sensor. The sensor provides an input voltage to
the PCM (Fig. 3). As coolant temperature varies, the
sensors resistance changes, resulting in a different
input voltage to the PCM. The PCM demands slightly richer air-fuel mixtures
and higher idle speeds until the engine reaches nor-
mal operating temperature. This sensor is also used for cooling fan control.
DISTRIBUTOR PICK-UPÐPCM INPUT
The distributor pick-up provides two inputs to the
PCM. From one input the PCM determines RPM (en-
gine speed). From the other input it derives crank-
shaft position. The PCM regulates injector
synchronization and adjusts ignition timing and en-
gine speed based on these inputs. The distributor pick-up contains two signal gener-
ators. The pick-up unit consists of 2 light emitting
diodes (LED), 2 photo diodes, and a separate timing
disk. The timing disk contains two sets of slots. Each
set of slots rotates between a light emitting diode
and a photo diode (Fig. 4). The inner set contains 6
large slots, one for each cylinder. The outer set con-
tains several smaller slots. The outer set of slots on the rotating disk repre-
sents 2 degrees of crankshaft rotation. Up to 1200
engine RPM, the PCM uses the input from the outer
set of slots to increase ignition timing accuracy. The outer set of slots contains a 10 degree flat spot
(Fig. 5). The flat spot tells the PCM that the next
piston at TDC will be number 6. The position of each
piston is referenced by one of the six inner slots (Fig.
5). As each slot on the timing disk passes between the
diodes, the beam from the light emitting diode is in-
Fig. 3 Coolant Temperature Sensor
Ä FUEL SYSTEMS 14 - 115

terrupted. This creates an alternating voltage in
each photo diode which is converted into on-off
pulses. The pulses are the input to the PCM. During cranking, the PCM cannot determine
crankshaft position until the 10 degree flat spot on
the outer set of slots passes through the optical unit.
Once the flat spot is detected, the PCM knows piston
number 6 will be the next piston at TDC. Since the disk rotates at half crankshaft speed, it
may take 2 engine revolutions during cranking for
the PCM to determine the position of piston number
6. For this reason the PCM will energize all six in-
jectors at the same time until it senses the position
of piston number 6.
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. 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 from
the MAP sensor voltage. Based on MAP sensor voltage and inputs from
other sensors, the PCM adjusts spark advance and
the air/fuel mixture. The MAP sensor (Fig. 6) mounts on a bracket at-
tached to the generator bracket. The sensor is con-
nected to the throttle body with a vacuum hose and
to the PCM electrically.
HEATED OXYGEN SENSOR (O2SENSOR)ÐPCM
INPUT
The O2sensor is located in the exhaust manifold
and provides an input voltage to the PCM. The input
tells the PCM the oxygen content of the exhaust gas
(Fig. 7). 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. When a large amount of oxygen is present
Fig. 4 Distributor Pick-up
Fig. 5 Inner and Outer Slots of Rotating Disk
Fig. 6 Map Sensor
Fig. 7 Heated Oxygen SensorÐ3.0L Engine
14 - 116 FUEL SYSTEMS Ä