tow CHEVROLET DYNASTY 1993 Manual Online

jector terminal in the harness connector. Repeat pro-
cedure for 2 to 3 injectors.
FUEL TANK
DRAINING FUEL TANK
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.
(1) Remove fuel filler cap.
(2) Perform the Fuel System Pressure Release pro-
cedure. (3) Remove ground cable from battery.
(4) Raise vehicle on hoist.
(5) Remove rubber cap from drain tube. The tube
is located on rear of fuel tank. Connect either a por-
table holding tank or a siphon hose to the drain tube
(Fig. 4). (6) Drain fuel tank into holding tank or a properly
labeled Gasoline safety container.
FUEL TANK REMOVAL
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.
(1) Perform fuel system pressure release.
(2) Drain fuel tank. Refer to Draining Fuel Tank
in this section. (3) Remove fuel filler tube to quarter panel screws
(Fig. 5). (4) Raise vehicle on hoist. Some models will re-
quire removal of the right rear wheel to access the
fuel filler tube.
WARNING: WRAP SHOP TOWELS AROUND HOSES
TO CATCH ANY GASOLINE SPILLAGE.
(5) Disconnect fuel pump and gauge sending unit
electrical connectors. (6) Disconnect the fuel supply and return hoses
from fuel pump. Refer to Quick Connect Hoses in the
Fuel Delivery section of this group. (7) Support tank with transmission jack. Loosen
tank mounting straps and lower tank slightly. Re-
move hose from pressure relief/rollover valve. (8) Carefully work fuel filler tube from tank.
(9) Remove tank mounting straps and lower tank.
(10) If removing tank from an flexible fuel AA-
body vehicle, inspect the heat shield. Replace as nec-
essary.
Fig. 3 Injector Harness ConnectorÐ2.2L/2.5L TBIFig. 4 Drain Tube Connection Location
14 - 16 FUEL SYSTEMS Ä

On AC, AG and AJ models, the A/C clutch is lo-
cated in the power distribution center. Refer to the
Wiring and Component Identification section of
Group 8W. ON AA and AP models, the A/C clutch relay is
mounted to the inner fender panel, next to the driv-
ers side strut tower (Fig. 10).
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-
sition, the PCM monitors the distributor pick-up sig-
nal. From the distributor signal, the PCM
determines engine speed and ignition timing (coil
dwell). If the PCM does not receive a distributor sig-
nal when the ignition switch is in the Run position,
it will de-energize both relays. When the relays are
de-energized, battery voltage is not supplied to the
fuel injector, ignition coil, fuel pump and oxygen sen-
sor heating element. On AC, AG and AJ models, the ASD relay and fuel
pump relay are located in the power distribution cen-
ter. Refer to the Wiring and Component Identifica-
tion section of Group 8W. On AA and AP models, the ASD relay and fuel
pump relay are mounted on the drivers side fender
well, next to the strut tower (Fig. 10).
IDLE AIR CONTROL MOTORÐPCM OUTPUT
The idle air control motor is mounted on the throt-
tle body (Fig. 11). The PCM operates the idle air con-
trol motor. The PCM adjusts engine idle speed
through the idle air control motor to compensate for
engine load or ambient 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 from the throttle position sensor, speed
sensor (distributor pick-up coil), coolant temperature
sensor, and various switch operations (brake, park/
neutral, air conditioning). Deceleration die out is also
prevented by increasing airflow when the throttle is
closed quickly after a driving (speed) condition.
EVAP CANISTER PURGE SOLENOIDÐPCM
OUTPUT
Vacuum for the Evaporative Canister is controlled
by the EVAP Canister Purge Solenoid (Fig. 12). The
solenoid is controlled by the PCM. The PCM operates the solenoid by switching the
ground circuit on and off based on engine operating
conditions. When grounded, the solenoid energizes
and prevents vacuum from reaching the evaporative
canister. When not energized, the solenoid allows
vacuum to flow to the canister. During warm-up and for a specified time period af-
ter hot starts, the PCM grounds the purge solenoid.
Vacuum does not operate the evaporative canister
valve.
Fig. 10 Relay Identification
Fig. 11 Idle Air Control Motor
Ä FUEL SYSTEMS 14 - 29

FUEL INJECTORÐPCM OUTPUT
The Fuel Injector is an electric solenoid operated
by the PCM (Fig. 15).
Based on sensor inputs, the PCM determines when
and how long the fuel injector should operate. The
amount of time the injector fires is referred to as in-
jector pulse width. The auto shutdown (ASD) relay
supplies battery voltage to the injector. The PCM
supplies the ground path. By switching the ground
path on and off, the PCM adjusts injector pulse
width. When the PCM supplies a ground path, a
spring loaded needle or armature lifts from its seat.
Fuel flows through the orifice and deflects off the
sharp edge of the injector nozzle. The resulting fuel
sprays forms a 45É cone shaped pattern before enter-
ing the air stream in the throttle body. Fuel is supplied to the injector constantly at regu-
lated 270 Kpa (39 psi). Unused fuel returns to the
fuel tank.
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.
IGNITION COILÐPCM OUTPUT
The PCM provides a ground contact (circuit) for en-
ergizing the ignition coil. When the PCM breaks the
contact, the energy in the coil primary transfers to
the secondary causing the spark. The PCM will de-
energize the ASD relay if it does not receive an input
from the distributor pick-up. Refer to Auto Shutdown
(ASD) Relay/Fuel Pump RelayÐPCM Output in this
section for relay operation. The ignition coil is mounted on the hot box next to
the thermostat housing (Fig. 16).
PART THROTTLE UNLOCK SOLENOIDÐPCM
OUTPUT
Three-speed automatic transaxles use a part throt-
tle unlock solenoid. The PCM controls the lock-up of
the torque convertor through the part throttle unlock
solenoid. The transaxle is locked up only in direct
drive mode. Refer to Group 21 for transaxle informa-
tion.
RADIATOR FAN RELAYÐPCM OUTPUT
The radiator fan is energized by the PCM through
the radiator fan relay. The PCM grounds the radia-
tor fan relay when engine coolant reaches a predeter-
mined temperature. For more information, refer to
Group 7, Cooling Systems. On AC, AG and AJ models, the radiator fan relay
is located in the power distribution center. Refer to
the Wiring and Component Identification section of
Group 8W. On AA and AP models, the radiator fan relay is
mounted on the drivers side fender well, next to the
strut tower (Fig. 10).
SPEED CONTROL SOLENOIDSÐPCM OUTPUT
The speed control vacuum and vent solenoids are
operated by the PCM. When the PCM supplies a
ground to the vacuum and vent solenoids, the speed
control system opens the throttle blade. When the
PCM supplies a ground only to the vent solenoid, the
throttle blade holds position. When the PCM removes
the ground from both the vacuum and vent solenoids,
the throttle blade closes. The PCM balances the two
solenoids to maintain the set speed. Refer to Group
8H for speed control information.
Fig. 15 Fuel Injector
Fig. 16 Ignition Coil
Ä FUEL SYSTEMS 14 - 31

(5) Remove throttle cable. If equipped, remove the
speed control and transaxle kickdown cables. (6) Remove return spring.
(7) Loosen fuel tube clamp on valve cover (Fig. 4).
(8) Wipe quick connect fittings to remove any dirt.
Remove fuel intake and return tubes. Refer to Fuel
Hoses, Clamps and Quick Connect Fittings in the
Fuel Delivery Section of this Group. Place a shop
towel under the connections to absorb any fuel spilled. (9) Remove throttle body mounting screws and lift
throttle body from vehicle. Remove throttle body gas-
ket from intake manifold.
INSTALLATION
(1) Using a new gasket, install throttle body and
tighten mounting screws to 20 N Im (175 in. lbs.)
torque. (2) Lubricate the ends of the fuel supply and return
tubes with clean 30 weight oil. Connect fuel lines to
quick connect fittings. Refer to Fuel Hoses, Clamps
and Quick Connect Fittings in the Fuel Delivery
Section of this Group . After the fuel tubes are
connected to the fittings, pull on the tubes to ensure
that they are fully inserted and locked into position. (3) Tighten the fuel tube clamp on the valve cover.
(4) Install return spring.
(5) Install throttle cable. If equipped, install kick-
down and speed control cables. (6) Install wiring connectors and vacuum hoses.
(7) Install air cleaner.
(8) Reconnect negative battery cable.
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. (9) With the ignition key in ON position, access the
DRBII scan tool ASD Fuel System Test to pressurize
the fuel system. Check for leaks.
FUEL FITTING
REMOVAL
(1) Remove air cleaner assembly.
(2) Perform Fuel System Pressure Release proce-
dure. (3) Disconnect negative battery cable.
(4) Loosen fuel tube clamp on valve cover.
(5) Wipe any dirt from around quick connect fittings.
(Fig. 5) Place a shop towel under the connections to
catch any spilled fuel. Remove fuel tubes from quick
connect fittings. Refer to Fuel Hoses, Clamps and
Quick Connect Fittings in the Fuel Delivery Sec-
tion of this Group .
(6) Remove each fitting from throttle body and note
inlet diameter. Remove copper washers.
INSTALLATION
(1) Replace copper washers with new washers.
(2) Install fuel fittings in proper ports and tighten to
20 N Im (175 in. lbs.) torque.
(3) Lubricate ends of the fuel tubes with 30 weight
oil. Insert the tubes into the quick connect fittings.
Refer to Fuel Hoses, Clamps and Quick Connect
Fittings in the Fuel Delivery Section of this
Group . After the fuel tubes are connected to the
fittings, pull on the tubes to ensure that they are fully
inserted and locked into position. (4) Tighten fuel tube clamp on valve cover.
(5) Reconnect negative battery cable.
Fig. 5 Servicing Fuel Fitting
Fig. 4 Fuel Line Clamp
14 - 50 FUEL SYSTEMS Ä

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 ignition key in ON position, access
the DRBII scan tool ASD Fuel System Test to pres-
surize the fuel system. Check for leaks. (7) Reinstall air cleaner assembly.
FUEL PRESSURE REGULATOR
The fuel pressure regulator is mounted on top of
the throttle body (Fig. 6).
REMOVAL
(1) Remove air cleaner assembly.
(2) Perform Fuel System Pressure Release proce-
dure. (3) Disconnect battery negative cable.
(4) Remove pressure regulator mounting screws
(Fig. 6).
WARNING: PLACE A SHOP TOWEL AROUND FUEL
INLET CHAMBER TO CONTAIN ANY FUEL REMAIN-
ING IN THE SYSTEM.
(5) Pull pressure regulator from the throttle body.
(6) Carefully remove O-ring from pressure regula-
tor and remove gasket.
INSTALLATION
(1) Place new gasket on pressure regulator. Care-
fully install new O-ring. (2) Position pressure regulator on throttle body.
Press regulator into place and install mounting
screws. Tighten screws to 5 N Im (40 in. lbs.) torque.
(3) 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. (4) With the ignition key in ON position, access
the DRBII scan tool ASD Fuel System Test to pres-
surize the fuel system. Check for leaks. (5) Reinstall air cleaner assembly.
FUEL INJECTOR
The fuel injector is installed in the top of the throt-
tle body. The injector is covered by a cap.
REMOVAL
(1) Remove air cleaner assembly.
(2) Perform Fuel System Pressure Release proce-
dure. (3) Disconnect negative cable from battery.
(4) Remove injector cap holddown screw (Torx-
head). (5) With two small screwdrivers, lift the top off the
injector using the slots provided (Fig. 7).
(6) Using a small screwdriver placed in the hole in
the front of the electrical connector, gently pry the
injector from the pod (Fig. 8).
Fig. 6 Servicing Fuel Pressure Regulator
Fig. 7 Removing Injector Cap
Fig. 8 Removing Fuel Injector
Ä FUEL SYSTEMS 14 - 51

(7) Ensure the injector lower O-ring has been re-
moved from the pod (Fig. 9).
INSTALLATION
(1) Apply a light coating of clean engine oil on the
O-rings. (2) Place assembly in the pod. Align the injector
wiring terminals with the injector cap fastener hole
(Fig. 10).
(3) Install injector cap with locating notch aligned
with the locating lobe on the injector (Fig. 11). (4) Push down on the cap to ensure a good seal.
(5) Rotate the cap and injector to line up the at-
tachment hole (Fig. 12).
(6) Install injector cap holddown screw (torx-head
screw). Tighten screw to 4-5 N Im (35-45 in. lbs.) torque.
(7) 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. (8) With the ignition key in ON position, access
the DRBII scan tool ASD Fuel System Test to pres-
surize the fuel system. Check for leaks. (9) Reinstall the air cleaner assembly.
THROTTLE POSITION SENSOR
REMOVAL
(1) Disconnect negative cable from battery.
(2) Remove air cleaner.
(3) Disconnect harness connector from throttle po-
sition sensor (Fig. 13). (4) Remove throttle position sensor mounting
screws. (5) Remove throttle position sensor from throttle
shaft.
INSTALLATION
(1) Install throttle position sensor to throttle body,
position toward the front of the vehicle. Tighten
screws to 2 N Im (20 in. lbs.) torque.
(2) Connect 3 way connector at throttle position
sensor.
Fig. 9 Servicing Fuel Injector
Fig. 10 Fuel Injector Installation
Fig. 11 Installing Fuel Injector Cap
Fig. 12 Fuel Injector Installed
14 - 52 FUEL SYSTEMS Ä

desired MAP value. Under idle conditions, the PCM
adjusts the idle air control motor to maintain a de-
sired engine speed.
AIR CONDITIONING (A/C) 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. With the engine operating, the PCM cycles the air
conditioning clutch on and off when the A/C switch
closes with the blower motor switch in the on posi-
tion. When the PCM senses low idle speeds or wide
open throttle through the throttle position sensor, it
de-energizes the A/C clutch relay. The relay contacts
open, preventing air conditioning clutch engagement. The A/C clutch relay is mounted to the inner
fender panel, next to the drivers side strut tower
(Fig. 11).
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-
sition, the PCM monitors the camshaft position sen-
sor (distributor pick-up) signal to determine engine
speed and ignition timing (coil dwell). If the PCM
does not receive a camshaft position sensor signal
when the ignition switch is in the Run position, it
de-energizes both relays. Battery voltage is not sup-
plied to the fuel injector, ignition coil, fuel pump and
oxygen sensor heating element. The ASD relay and fuel pump relay are mounted
on the drivers side fender well, next to the strut
tower (Fig. 11).
DUTY CYCLE EVAP PURGE SOLENOIDÐPCM
OUTPUT
The duty cycle EVAP purge solenoid regulates the
rate of vapor flow from the EVAP canister to the
throttle body. The powertrain control module oper-
ates the solenoid. During the cold start warm-up period and the hot
start time delay, the PCM does not energize the so-
lenoid. When de-energized, no vapors are purged.
The PCM de-energizes the solenoid during open loop
operation. The engine enters closed loop operation after it
reaches a specified temperature and the time delay
ends. During closed loop operation, the PCM ener-
gizes and de-energizes the solenoid approximately 5
to 10 times per second, depending upon operating
conditions. The PCM varies the vapor flow rate by
changing solenoid pulse width. Pulse width is the
amount of time the solenoid energizes. A rubber boot covers the EVAP purge solenoid.
The solenoid and bracket attach to the EVAP canis-
Fig. 12 EVAP Purge Solenoid
Fig. 11 Relay Identification
Ä FUEL SYSTEMS 14 - 61

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 and by using stored default values.Signals that can trigger the Malfunction Indi-
cator (Check Engine) Lamp.
² An emission system component
² Battery Voltage Input
² Charging system
² Engine Coolant Temperature Sensor
² Manifold Absolute Pressure Sensor
² Methanol Concentration Sensor
² Throttle Position Sensor
The malfunction indicator lamp can also display
diagnostic trouble codes. Cycle the ignition switch on,
off, on, off, on, within five seconds and the PCM
displays any diagnostic trouble codes stored in
memory. Refer to the 2.5L Flexible Fuel Multi-Port
Fuel InjectionÐOn Board Diagnostics section in this
group for diagnostic trouble code descriptions.
RADIATOR FAN RELAYÐPCM OUTPUT
The radiator fan is energized by the PCM through
the radiator fan relay. The PCM grounds the radiator
fan relay when engine coolant reaches a predetermined
temperature. For more information, refer to Group 7,
Cooling Systems. The radiator fan relay is mounted on the drivers side
fender well, next to the strut tower (Fig. 11).
SPEED CONTROL SOLENOIDSÐPCM OUTPUT
The speed control vacuum and vent solenoids are
operated by the PCM. When the PCM supplies a
ground to the vacuum and vent solenoids, the speed
control system opens the throttle blade. When the PCM
supplies a ground only to the vent solenoid, the throttle
blade holds position. When the PCM removes the
ground from both the vacuum and vent solenoids, the
throttle blade closes. The PCM balances the two sole-
noids to maintain the set speed. Refer to Group 8H for
speed control information.
TACHOMETERÐPCM OUTPUT
The PCM supplies engine RPM to the instrument
panel tachometer. Refer to Group 8 for tachometer
information.
TORQUE CONVERTER CLUTCH SOLENOIDÐPCM
OUTPUT
Three-speed automatic transaxles use a torque con-
verter clutch solenoid. The PCM controls the lock-up of
the torque convertor through the solenoid. The tran-
saxle is locked up only in direct drive mode. Refer to
Group 21 for transaxle information.
MODES OF OPERATION
As input signals to the PCM change, the PCM
adjusts its response to the output devices. For example, the PCM must calculate a different injector pulse
width and ignition timing for idle than it does for wide
open throttle (WOT). There are several different modes
of operation that determine how the PCM responds to
the various input signals. There are two different areas of operation, Open
Loop and Closed Loop. During Open Loop modes, the PCM receives input
signals and responds according to preset PCM pro-
gramming. Input from the oxygen (O
2) sensor is not
monitored during Open Loop modes. During CLOSED LOOP modes, the PCM does moni-
tor the oxygen (O
2) sensor input. The input indicates if
the calculated injector pulse width results in the ideal
air-fuel ratio for the current percentage of methanol in
the fuel. By monitoring the exhaust oxygen content
through the O
2sensor, the PCM can fine tune the
injector pulse width to achieve optimum fuel economy
combined with low emissions. The 2.5L flexible fuel multi-port fuel injection system
has the following modes of operation:
² Ignition switch ON - Zero RPM
² Engine start-up
² Engine warm-up
² Cruise (Idle)
² Acceleration
² Deceleration
² Wide Open Throttle
² Ignition switch OFF
The engine start-up (crank), engine warm-up, and
wide open throttle modes are OPEN LOOP modes. The
acceleration, deceleration, and cruise modes, with the
engine at operating temperature are CLOSED
LOOP modes (under most operating conditions).
IGNITION SWITCH ON (ZERO RPM) MODE
When the ignition switch cycles and past the On
position, the fuel injection system activates and the
following actions occur:
² For two seconds at key ON (and during cranking),
the methanol concentration sensor calibrates the PCM.
During the calibration period the sensor sends 4.45
volts to the PCM as a correction factor. After the
calibration period, the methanol concentration sensor
output represents the methanol percentage in the fuel.
² The PCM calculates basic fuel strategy by determin-
ing atmospheric air pressure from the MAP sensor
input.
² The PCM monitors the coolant temperature sensor
and throttle position sensor input. The PCM modifies
fuel strategy based on this input. When the key is in the ON position and the engine is
not running, the auto shutdown (ASD) relay and fuel
pump relay are not energized. Therefore battery volt-
age is not supplied to the fuel pump, ignition coil, fuel
injector or oxygen sensor heating element.
Ä FUEL SYSTEMS 14 - 63

(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

noid is energized. The solenoid mounts to the passen-
ger side inner fender panel, next to the strut tower
(Fig. 17).
MODES OF OPERATION
As input signals to the PCM change, the PCM
adjusts its response to the output devices. For example,
the PCM must calculate a different injector pulse
width and ignition timing for idle than it does for wide
open throttle (WOT). There are several different modes
of operation that determine how the PCM responds to
the various input signals. There are two different areas of operation, OPEN
LOOP and CLOSED LOOP. During OPEN LOOP modes, the PCM receives input
signals and responds according to preset PCM pro-
gramming. Input from the oxygen (O
2) sensor is not
monitored during OPEN LOOP modes. During CLOSED LOOP modes, the PCM does moni-
tor the oxygen (O
2) sensor input. This input indicates
to the PCM whether or not the calculated injector pulse
width results in the ideal air-fuel ratio of 14.7 parts air
to 1 part fuel. By monitoring the exhaust oxygen
content through the O
2sensor, the PCM can fine tune
the injector pulse width to achieve optimum fuel
economy combined with low emissions. The 2.2L Turbo III multi-port fuel injection system
has the following modes of operation:
² Ignition switch ON - Zero RPM
² Engine start-up
² Engine warm-up
² Cruise (Idle)
² Acceleration
² Deceleration
² Wide Open Throttle
² Ignition switch OFF
The engine start-up (crank), engine warm-up, and
wide open throttle modes are OPEN LOOP modes. The
acceleration, deceleration, and cruise modes, with the
engine at operating temperature are CLOSED
LOOP modes (under most operating conditions).
IGNITION SWITCH ON (ZERO RPM) MODE
When the ignition switch activates the fuel injection
system the following actions occur:
²
The PCM calculates basic fuel strategy by determining
atmospheric air pressure from the MAP sensor input.
² The PCM monitors the coolant temperature sensor
and throttle position sensor input. The PCM modifies
fuel strategy based on this input. When the key is in the ON position and the engine is
not running, the auto shutdown (ASD) relay and fuel
pump relay are not energized. Therefore battery volt-
age is not supplied to the fuel pump, ignition coil, fuel
injector or oxygen sensor heating element.
ENGINE START-UP MODE
This is an OPEN LOOP mode. The following actions
occur when the starter motor is engaged. If the PCM receives the camshaft position and crank-
shaft position sensor signals, it energizes the auto
shutdown (ASD) relay and fuel pump relay. These
relays supply battery voltage to the fuel pump, fuel
injectors, ignition coil, and oxygen sensor heating ele-
ment. If the PCM does not receive the camshaft posi-
tion sensor and crankshaft position sensor signals
within approximately one second, it de-energizes the
ASD relay and fuel pump relay. The PCM energizes all injectors until it determines
crankshaft position from the camshaft position sensor
and crankshaft position sensor signals. The PCM de-
termines crankshaft position within 1 engine revolu-
tion. After determining crankshaft position, the PCM be-
gins energizing the injectors in sequence. The PCM
adjusts injector pulse width and controls injector syn-
chronization by turning the individual ground paths to
the injectors On and Off. When the engine idles within 664 RPM of its target
RPM, the PCM compares current MAP sensor value
with the atmospheric pressure value received during
the Ignition Switch On (zero RPM) mode. If the PCM
does not detect a minimum difference between the two
values, it sets a MAP fault into memory. Once the ASD and fuel pump relays have been
energized, the PCM:
² Determines injector pulse width based on coolant
temperature, manifold absolute pressure (MAP) and
the number of engine revolutions since cranking was
initiated.
² Monitors the coolant temperature sensor, camshaft
position sensor, crankshaft position sensor, MAP sen-
sor, and throttle position sensor to determine correct
ignition timing.
ENGINE WARM-UP MODE
This is a OPEN LOOP mode. The following inputs
are received by the PCM:
² engine coolant temperature
² knock sensor
² manifold absolute pressure (MAP)
² engine speed (crankshaft position sensor)
² throttle position
² A/C switch
² battery voltage
The PCM provides a ground path for the injectors to
precisely control injector pulse width (by switching the
ground on and off). The PCM adjusts engine idle speed
through the idle air control motor. Also, the PCM
regulates ignition timing.
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