fuel pressure CHRYSLER CARAVAN 2003 Workshop Manual
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Page 1367 of 2177
FUEL PUMP MODULE
DESCRIPTION
The fuel pump module is installed in the top of the
fuel tank (Fig. 10) .
The fuel pump module contains the following:
²Electric fuel pump
²Fuel pump reservoir
²Inlet strainer
²Fuel pressure regulator
²Fuel gauge sending unit
²Fuel supply line connection
The inlet strainer, fuel pressure regulator
and fuel level sensor are the only serviceable
items. If the fuel pump or electrical wiring har-
ness requires service, replace the fuel pump
module.
The electric fuel pump is located in and is part of
the fuel pump module. It is a positive displacement,
gerotor type, immersible pump with a permanent
magnet electric motor.
OPERATION
The pump draws fuel through a strainer and
pushes it through the motor to the outlet. The pump
contains one check valve. The check valve, in the
pump outlet, maintains pump pressure during engine
off conditions. The fuel pump relay provides voltage
to the fuel pump.
The fuel pump has a maximum deadheaded pres-
sure output of approximately 880 kPa (130 psi). The
regulator adjusts fuel system pressure to approxi-
mately 400 34 kPa (58 5 psi).
FUEL PUMP ELECTRICAL CONTROL
Voltage to operate the electric pump is supplied
through the fuel pump relay. For an electrical opera-
tional description of the fuel pump refer to fuel Pump
RelayÐPCM Output.
ELECTRICAL PUMP REPLACEMENT
The electric fuel pump is not serviceable. If the
fuel pump or electrical wiring harness needs replace-
ment, the complete fuel pump module must be
replaced. Perform the Fuel System Pressure Release
procedure before servicing the fuel pump.
REMOVAL
WARNING: RELEASE FUEL SYSTEM PRESSURE
BEFORE SERVICING FUEL SYSTEM COMPONENTS.
SERVICE VEHICLES IN WELL VENTILATED AREAS
AND AVOID IGNITION SOURCES. NEVER SMOKE
WHILE SERVICING THE VEHICLE.
(1) Remove fuel filler cap and perform Fuel Sys-
tem Pressure Release procedure.
(2) Disconnect negative cable from auxiliary
jumper terminal.
(3) Drain fuel tank, refer to the Fuel Tank proce-
dure in the Fuel Delivery section.
(4) Remove fuel tank, refer to the Fuel Tank
removal section.
(5) Clean top of tank to remove loose dirt and
debris.
(6) Using a brass punch and hammer remove lock-
nut to release pump module (Fig. 11).
Fig. 10 Fuel Pump Module
1 - INLET STRAINER
2 - FUEL RESERVOIR
3 - FUEL PRESSURE REGULATOR
4 - FUEL LEVEL SENSOR
Fig. 11 FUEL PUMP MODULE LOCKING RING
14 - 8 FUEL DELIVERYRS
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WARNING: THE FUEL RESERVOIR OF THE FUEL
PUMP MODULE DOES NOT EMPTY OUT WHEN THE
TANK IS DRAINED. THE FUEL IN THE RESERVOIR
MAY SPILL OUT WHEN THE MODULE IS REMOVED.
(7) Remove fuel pump module and O-ring from
tank (Fig. 12). Discard O-ring.
INSTALLATION
NOTE: Be careful not to allow dirt/debris to fall into
the fuel tank.
(1) Wipe seal area of tank clean and place a new
O-ring seal in position on pump.
(2) Position fuel pump module in tank.
(3) Tighten lockring using a brass punch and ham-
mer to install the lockring (Fig. 11).
(4) Install fuel tank, refer to the Fuel Tank instal-
lation section.
(5) Lower vehicle.
(6) Connect negative cable battery.
(7) Fill fuel tank. Use the DRB IIItscan tool to
pressurize the fuel system. Check for leaks.
(8) Install fuel filler cap.
FUEL RAIL
REMOVAL
REMOVAL - 2.4L
(1) Perform fuel system pressure release procedure
before servicing or starting repairs.Refer to
Fuel System Pressure Release Procedure in this sec-
tion.(2) Disconnect negative cable from battery.
(3) Disconnect the wiring connectors for fuel injec-
tors harness (Fig. 13).
(4) Remove wiring harness from brackets.
(5) Disconnect the connectors from the fuel injec-
tors.
(6) Remove harness from vehicle.
(7) Remove fuel hose quick connect fitting from the
chassis tube.Refer to Fuel Hoses, Clamps and
Quick Connect Fittings in this Section.Place a
shop towel under the connections to absorb any fuel
spilled from the fitting.
WARNING: WRAP A SHOP TOWEL AROUND HOSES
TO CATCH ANY GASOLINE SPILLAGE.
(8) Remove fuel rail attaching bolts.
(9) Remove fuel rail. Be careful not to damage the
injector O-rings upon removal from their ports.
REMOVAL - 3.3/3.8L
(1) Perform fuel system pressure release procedure
before servicing or starting repairs.Refer to
Fuel System Pressure Release Procedure in this sec-
tion.
(2) Disconnect negative cable from battery.
(3) Remove upper intake manifold, refer to the
Engine/Manifolds/Upper Intake for more informa-
tion..
(4) Cover intake manifold with suitable cover
when servicing.
(5) Remove the fuel hose quick connect fitting from
the chassis tube.Refer to Fuel Hoses, Clamps
and Quick Connect Fittings in this Section.
WARNING: WRAP A SHOP TOWEL AROUND HOSES
TO CATCH ANY GASOLINE SPILLAGE.
(6) Remove the fuel rail attaching bolts (Fig. 14).
Fig. 12 Fuel Pump Module Removal
1 - FUEL PUMP MODULE
2 - O-RING
Fig. 13 FUEL RAIL AND INJECTORS 2.4L
1 - Fuel Injectors
2 - Fuel Rail
RSFUEL DELIVERY14-9
FUEL PUMP MODULE (Continued)
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REMOVAL
(1) Remove fuel filler cap and perform Fuel Sys-
tem Pressure Release procedure (Fig. 15).
(2) Disconnect negative cable from battery.
(3) Insert fuel siphon hose into fuel filler neck and
push it into the tank.
(4) Drain fuel tank dry into holding tank or a
properly labeledGASOLINEsafety container.
(5) Raise vehicle on hoist and support.
(6) Use a transmission jack to support fuel tank.
Remove bolts from fuel tank straps.
(7) Lower tank slightly.
(8) Disconnect the fuel filler vent tube. Squeeze
tabs and pull apart (Fig. 16).
(9) Disconnect the fuel fill hose at the fuel tank
filler metal tubeNOT AT THE FUEL TANK(Fig.
16).
(10) Disconnect fuel line and vapor line at the
front of the fuel tank.
The fuel pump module electrical connector
has a retainer that locks it in place.
(11) Slide fuel pump module electrical connector
lock to unlock (Fig. 17).
(12) Push down on connector retainer (Fig. 18) and
pull connector off module.
(13) Lower tank from vehicle. Remove fuel filler
vent tube from frame (Fig. 19).
INSTALLATION
(1) Position fuel tank on transmission jack. Con-
nect rollover valve hose. Connect fuel filler tube vent
hose and tighten clamp.
(2) Raise tank into position and carefully work
filler metal tube into the rubber hose on fuel tank. A
light coating of clean engine oil on the tube end may
be used to aid assembly.
(3) Feed filler vent line thru frame rail. Careful
not to cross lines.
Fig. 15 Fuel Tank
1 - ROLLOVER VALVE
2 - FUEL FILLER INLET
3 - ROLLOVER VALVE
4 - GROUND STRAP
5 - FUEL FILTER
6 - FUEL PUMP MODULEFig. 16 FUEL FILLER AND VENT TUBE
1 - Filler Tube
2 - Vent Tube
Fig. 17 Fuel Line Retainers and Pump Connector
Lock
1 - PUSH
2 - CONNECTOR LOCK
3 - QUICK CONNECT RETAINERS
RSFUEL DELIVERY14-11
FUEL TANK (Continued)
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WARNING: RELEASE FUEL SYSTEM PRESSURE
BEFORE DISCONNECTING A QUICK-CONNECT FIT-
TINGS. REFER TO THE FUEL PRESSURE RELEASE
PROCEDURE.
(1) Perform Fuel Pressure Release Procedure.
Refer to the Fuel Pressure Release Procedure in this
section.
(2) Disconnect negative cable from battery or aux-
iliary jumper terminal.
(3) Squeeze retainer tabs together and pull fuel
tube/quick-connect fitting assembly off of fuel tube
nipple. The retainer will remain on fuel tube.
INSTALLATION
CAUTION: Never install a quick-connect fitting with-
out the retainer being either on the fuel tube or
already in the quick-connect fitting. In either case,
ensure the retainer locks securely into the quick-
connect fitting by firmly pulling on fuel tube and fit-
ting to ensure it is secured.
(1) Using a clean lint free cloth, clean the fuel tube
nipple and retainer.
(2) Prior to connecting the fitting to the fuel tube,
coat the fuel tube nipple with clean engine oil.
(3) Push the quick-connect fitting over the fuel
tube until theretainer seats and a click is heard.
(4) The plastic quick-connect fitting has windows
in the sides of the casing. When the fitting com-
pletely attaches to the fuel tube, the retainer locking
ears and the fuel tube shoulder are visible in the
windows. If they are not visible, the retainer was not
properly installed (Fig. 24).Do not rely upon the
audible click to confirm a secure connection.
(5) Connect negative cable to battery or auxiliary
jumper terminal.CAUTION: When using the ASD Fuel System Test,
the Auto Shutdown (ASD) Relay remains energized
for several minutes, until the test is stopped, or
until the ignition switch is turned to the Off posi-
tion.
(6) Use the DRB IIItscan tool ASD Fuel System
Test to pressurize the fuel system. Check for leaks.
TWO-TAB TYPE FITTING
This type of fitting is equipped with tabs located on
both sides of the fitting (Fig. 25). These tabs are sup-
plied for disconnecting the quick-connect fitting from
component being serviced.
CAUTION: The interior components (O-rings, spac-
ers) of this type of quick-connect fitting are not ser-
viced separately, but new plastic retainers are
available. Do not attempt to repair damaged fittings
or fuel lines/tubes. If repair is necessary, replace
the complete fuel tube assembly.
WARNING: THE FUEL SYSTEM IS UNDER A CON-
STANT PRESSURE (EVEN WITH THE ENGINE OFF).
BEFORE SERVICING ANY FUEL SYSTEM HOSES,
FITTINGS OR LINES, THE FUEL SYSTEM PRES-
SURE MUST BE RELEASED. REFER TO THE FUEL
PRESSURE RELEASE PROCEDURE IN THIS
GROUP.
DISCONNECTION/CONNECTION
(1) Perform fuel pressure release procedure. Refer
to Fuel Pressure Release Procedure in this group.
(2) Disconnect negative battery cable from battery
or auxiliary jumper terminal.
Fig. 24 Plastic Quick-Connect Fitting/Fuel Tube
Connection
1 - WINDOW
2-TAB(2)
3 - EAR
4 - SHOULDER (ON TUBE)
Fig. 25 Typical Two-Tab Type Quick-Connect Fitting
1 - TAB(S)
2 - QUICK-CONNECT FITTING
14 - 14 FUEL DELIVERYRS
QUICK CONNECT FITTING (Continued)
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Page 1374 of 2177
(3) Clean fitting of any foreign material before dis-
assembly.
(4) To disconnect quick-connect fitting, squeeze
plastic retainer tabs (Fig. 25) against sides of quick-
connect fitting with your fingers. Tool use is not
required for removal and may damage plastic
retainer. Pull fitting from fuel system component
being serviced. The plastic retainer will remain on
component being serviced after fitting is discon-
nected. The O-rings and spacer will remain in quick-
connect fitting connector body.
(5) Inspect quick-connect fitting body and compo-
nent for damage. Replace as necessary.
CAUTION: When the quick-connect fitting was dis-
connected, the plastic retainer will remain on the
component being serviced. If this retainer must be
removed, very carefully release the retainer from
the component with two small screwdrivers. After
removal, inspect the retainer for cracks or any dam-
age.
(6) Prior to connecting quick-connect fitting to
component being serviced, check condition of fitting
and component. Clean parts with a lint-free cloth.
Lubricate with clean engine oil.
(7) Insert quick-connect fitting to component being
serviced and into plastic retainer. When a connection
is made, a click will be heard.
(8) Verify a locked condition by firmly pulling on
fuel tube and fitting (15-30 lbs.).
(9) Connect negative cable to battery or auxiliary
jumper terminal.
(10) Use the DRB IIItscan tool ASD Fuel System
Test to pressurize the fuel system. Check for leaks.
PLASTIC RETAINER RING TYPE FITTING
This type of fitting can be identified by the use of a
full-round plastic retainer ring (Fig. 26) usually black
in color.
CAUTION: The interior components (O-rings, spac-
ers, retainers) of this type of quick-connect fitting
are not serviced separately. Do not attempt to repair
damaged fittings or fuel lines/tubes. If repair is nec-
essary, replace the complete fuel tube assembly.
WARNING: THE FUEL SYSTEM IS UNDER A CON-
STANT PRESSURE (EVEN WITH THE ENGINE OFF).
BEFORE SERVICING ANY FUEL SYSTEM HOSES,
FITTINGS OR LINES, THE FUEL SYSTEM PRES-
SURE MUST BE RELEASED. REFER TO THE FUEL
SYSTEM PRESSURE RELEASE PROCEDURE IN
THIS GROUP.DISCONNECTION/CONNECTION
(1) Perform fuel pressure release procedure. Refer
to Fuel Pressure Release Procedure in this section.
(2) Disconnect negative battery cable from battery
or auxiliary jumper terminal.
(3) Clean fitting of any foreign material before dis-
assembly.
(4) To release fuel system component from quick-
connect fitting, firmly push fitting towards compo-
nent being serviced while firmly pushing plastic
retainer ring into fitting (Fig. 26). With plastic ring
depressed, pull fitting from component.The plastic
retainer ring must be pressed squarely into fit-
ting body. If this retainer is cocked during
removal, it may be difficult to disconnect fit-
ting. Use an open-end wrench on shoulder of
plastic retainer ring to aid in disconnection.
(5) After disconnection, plastic retainer ring will
remain with quick-connect fitting connector body.
(6) Inspect fitting connector body, plastic retainer
ring and fuel system component for damage. Replace
as necessary.
(7) Prior to connecting quick-connect fitting to
component being serviced, check condition of fitting
and component. Clean parts with a lint-free cloth.
Lubricate with clean engine oil.
Fig. 26 Plastic Retainer Ring Type Fitting
1 - FUEL TUBE
2 - QUICK CONNECT FITTING
3 - PUSH
4 - PLASTIC RETAINER
5 - PUSH
6 - PUSH
7 - PUSH
8 - PUSH
RSFUEL DELIVERY14-15
QUICK CONNECT FITTING (Continued)
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FUEL INJECTION
OPERATION
OPERATION - INJECTION SYSTEM
All engines used in this section have a sequential
Multi-Port Electronic Fuel Injection system. The MPI
system is computer regulated and provides precise
air/fuel ratios for all driving conditions. The Power-
train Control Module (PCM) operates the fuel injec-
tion system.
The PCM regulates:
²Ignition timing
²Air/fuel ratio
²Emission control devices
²Cooling fan
²Charging system
²Idle speed
²Vehicle speed control
Various sensors provide the inputs necessary for
the PCM to correctly operate these systems. In addi-
tion to the sensors, various switches also provide
inputs to the PCM.
The PCM can adapt its programming to meet
changing operating conditions.
Fuel is injected into the intake port above the
intake valve in precise metered amounts through
electrically operated injectors. The PCM fires the
injectors in a specific sequence. Under most operat-
ing conditions, the PCM maintains an air fuel ratio
of 14.7 parts air to 1 part fuel by constantly adjust-
ing injector pulse width. Injector pulse width is the
length of time the injector is open.
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 theprimaryinputs that determine
injector pulse width.
OPERATION - MODES OF OPERATION
As input signals to the PCM change, the PCM
adjusts its response to 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 differ-
ent 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
programming. Inputs from the upstream and down-
stream heated oxygen sensors are not monitored dur-
ing OPEN LOOP modes, except for heated oxygensensor diagnostics (they are checked for shorted con-
ditions at all times).
During CLOSED LOOP modes the PCM monitors
the inputs from the upstream and downstream
heated oxygen sensors. The upstream heated oxygen
sensor input tells the PCM if the calculated injector
pulse width resulted in the ideal air-fuel ratio of 14.7
to one. By monitoring the exhaust oxygen content
through the upstream heated oxygen sensor, the
PCM can fine tune injector pulse width. Fine tuning
injector pulse width allows the PCM to achieve opti-
mum fuel economy combined with low emissions.
For the PCM to enter CLOSED LOOP operation,
the following must occur:
(1) Engine coolant temperature must be over 35ÉF.
²If the coolant is over 35ÉF the PCM will wait 38
seconds.
²If the coolant is over 50ÉF the PCM will wait 15
seconds.
²If the coolant is over 167ÉF the PCM will wait 3
seconds.
(2) For other temperatures the PCM will interpo-
late the correct waiting time.
(3) O2 sensor must read either greater than 0.745
volts or less than 0.29 volt.
(4) The multi-port fuel injection systems has the
following modes of operation:
²Ignition switch ON (Zero RPM)
²Engine start-up
²Engine warm-up
²Cruise
²Idle
²Acceleration
²Deceleration
²Wide Open Throttle
²Ignition switch OFF
(5) The engine start-up (crank), engine warm-up,
deceleration with fuel shutoff and wide open throttle
modes are OPEN LOOP modes. Under most operat-
ing conditions, the acceleration, deceleration (with
A/C on), idle and cruise modes,with the engine at
operating temperatureare CLOSED LOOP modes.
IGNITION SWITCH ON (ZERO RPM) MODE
When the ignition switch activates the fuel injec-
tion system, the following actions occur:
²The PCM monitors the engine coolant tempera-
ture sensor and throttle position sensor input. The
PCM determines basic fuel injector pulse width from
this input.
²The PCM determines atmospheric air pressure
from the MAP sensor input to modify injector pulse
width.
When the key is in the ON position and the engine
is not running (zero rpm), the Auto Shutdown (ASD)
and fuel pump relays de-energize after approximately
14 - 18 FUEL INJECTIONRS
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1 second. Therefore, battery voltage is not supplied to
the fuel pump, ignition coil, fuel injectors and heated
oxygen sensors.
ENGINE START-UP MODE
This is an OPEN LOOP mode. If the vehicle is in
park or neutral (automatic transaxles) or the clutch
pedal is depressed (manual transaxles) the ignition
switch energizes the starter relay when the engine is
not running. The following actions occur when the
starter motor is engaged.
²If the PCM receives the camshaft position sensor
and crankshaft position sensor signals, it energizes
the Auto Shutdown (ASD) relay and fuel pump relay.
If the PCM does not receive both signals within
approximately one second, it will not energize the
ASD relay and fuel pump relay. The ASD and fuel
pump relays supply battery voltage to the fuel pump,
fuel injectors, ignition coil, (EGR solenoid and PCV
heater if equipped) and heated oxygen sensors.
²The PCM energizes the injectors (on the 69É
degree falling edge) for a calculated pulse width until
it determines crankshaft position from the camshaft
position sensor and crankshaft position sensor sig-
nals. The PCM determines crankshaft position within
1 engine revolution.
²After determining crankshaft position, the PCM
begins energizing the injectors in sequence. It adjusts
injector pulse width and controls injector synchroni-
zation by turning the individual ground paths to the
injectors On and Off.
²When the engine idles within 64 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.
Once the ASD and fuel pump relays have been
energized, the PCM determines injector pulse width
based on the following:
²MAP
²Engine RPM
²Battery voltage
²Engine coolant temperature
²Inlet/Intake air temperature (IAT)
²Throttle position
²The number of engine revolutions since cranking
was initiated
During Start-up the PCM maintains ignition tim-
ing at 9É BTDC.
ENGINE WARM-UP MODE
This is an OPEN LOOP mode. The following inputs
are received by the PCM:
²Manifold Absolute Pressure (MAP)
²Crankshaft position (engine speed)
²Engine coolant temperature
²Inlet/Intake air temperature (IAT)²Camshaft position
²Knock sensor
²Throttle position
²A/C switch status
²Battery voltage
²Vehicle speed
²Speed control
²O2 sensors
The PCM adjusts injector pulse width and controls
injector synchronization by turning the individual
ground paths to the injectors On and Off.
The PCM adjusts ignition timing and engine idle
speed. Engine idle speed is adjusted through the idle
air control motor.
CRUISE OR IDLE MODE
When the engine is at operating temperature this
is a CLOSED LOOP mode. During cruising or idle
the following inputs are received by the PCM:
²Manifold absolute pressure
²Crankshaft position (engine speed)
²Inlet/Intake air temperature
²Engine coolant temperature
²Camshaft position
²Knock sensor
²Throttle position
²Exhaust gas oxygen content (O2 sensors)
²A/C switch status
²Battery voltage
²Vehicle speed
The PCM adjusts injector pulse width and controls
injector synchronization by turning the individual
ground paths to the injectors On and Off.
The PCM adjusts engine idle speed and ignition
timing. The PCM adjusts the air/fuel ratio according
to the oxygen content in the exhaust gas (measured
by the upstream and downstream heated oxygen sen-
sor).
The PCM monitors for engine misfire. During
active misfire and depending on the severity, the
PCM either continuously illuminates or flashes the
malfunction indicator lamp (Check Engine light on
instrument panel). Also, the PCM stores an engine
misfire DTC in memory, if 2nd trip with fault.
The PCM performs several diagnostic routines.
They include:
²Oxygen sensor monitor
²Downstream heated oxygen sensor diagnostics
during open loop operation (except for shorted)
²Fuel system monitor
²EGR monitor (if equipped)
²Purge system monitor
²Catalyst efficiency monitor
²All inputs monitored for proper voltage range,
rationality.
RSFUEL INJECTION14-19
FUEL INJECTION (Continued)
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²All monitored components (refer to the Emission
section for On-Board Diagnostics).
The PCM compares the upstream and downstream
heated oxygen sensor inputs to measure catalytic
convertor efficiency. If the catalyst efficiency drops
below the minimum acceptable percentage, the PCM
stores a diagnostic trouble code in memory, after 2
trips.
During certain idle conditions, the PCM may enter
a variable idle speed strategy. During variable idle
speed strategy the PCM adjusts engine speed based
on the following inputs.
²A/C status
²Battery voltage
²Battery temperature or Calculated Battery Tem-
perature
²Engine coolant temperature
²Engine run time
²Inlet/Intake air temperature
²Vehicle mileage
ACCELERATION MODE
This is a CLOSED LOOP mode. The PCM recog-
nizes an abrupt increase in Throttle Position sensor
output voltage or MAP sensor output voltage as a
demand for increased engine output and vehicle
acceleration. The PCM increases injector pulse width
in response to increased fuel demand.
²Wide Open Throttle-open loop
DECELERATION MODE
This is a CLOSED LOOP mode. During decelera-
tion the following inputs are received by the PCM:
²A/C status
²Battery voltage
²Inlet/Intake air temperature
²Engine coolant temperature
²Crankshaft position (engine speed)
²Exhaust gas oxygen content (upstream heated
oxygen sensor)
²Knock sensor
²Manifold absolute pressure
²Throttle position sensor
²IAC motor (solenoid) control changes in response
to MAP sensor feedback
The PCM may receive a closed throttle input from
the Throttle Position Sensor (TPS) when it senses an
abrupt decrease in manifold pressure. This indicates
a hard deceleration (Open Loop). In response, the
PCM may momentarily turn off the injectors. This
helps improve fuel economy, emissions and engine
braking.
WIDE-OPEN-THROTTLE MODE
This is an OPEN LOOP mode. During wide-open-
throttle operation, the following inputs are used by
the PCM:
²Inlet/Intake air temperature
²Engine coolant temperature
²Engine speed
²Knock sensor
²Manifold absolute pressure
²Throttle position
When the PCM senses a wide-open-throttle condi-
tion through the Throttle Position Sensor (TPS) it de-
energizes the A/C compressor clutch relay. This
disables the air conditioning system and disables
EGR (if equipped).
The PCM adjusts injector pulse width to supply a
predetermined amount of additional fuel, based on
MAP and RPM.
IGNITION SWITCH OFF MODE
When the operator turns the ignition switch to the
OFF position, the following occurs:
²All outputs are turned off, unless 02 Heater
Monitor test is being run. Refer to the Emission sec-
tion for On-Board Diagnostics.
²No inputs are monitored except for the heated
oxygen sensors. The PCM monitors the heating ele-
ments in the oxygen sensors and then shuts down.
FUEL CORRECTION or ADAPTIVE MEMORIES
DESCRIPTION
In Open Loop, the PCM changes pulse width with-
out feedback from the O2 Sensors. Once the engine
warms up to approximately 30 to 35É F, the PCM
goes into closed loopShort Term Correctionand
utilizes feedback from the O2 Sensors. Closed loop
Long Term Adaptive Memoryis maintained above
170É to 190É F unless the PCM senses wide open
throttle. At that time the PCM returns to Open Loop
operation.
OPERATION
Short Term
The first fuel correction program that begins func-
tioning is the short term fuel correction. This system
corrects fuel delivery in direct proportion to the read-
ings from the Upstream O2 Sensor.
The PCM monitors the air/fuel ratio by using the
input voltage from the O2 Sensor. When the voltage
reaches its preset high or low limit, the PCM begins
to add or remove fuel until the sensor reaches its
switch point. The short term corrections then begin.
The PCM makes a series of quick changes in the
injector pulse-width until the O2 Sensor reaches its
14 - 20 FUEL INJECTIONRS
FUEL INJECTION (Continued)
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Page 1380 of 2177
opposite preset limit or switch point. The process
then repeats itself in the opposite direction.
Short term fuel correction will keep increasing or
decreasing injector pulse-width based upon the
upstream O2 Sensor input. The maximum range of
authority for short term memory is 25% (+/-) of base
pulse-width. Short term is violated and is lost when
ignition is turned OFF.
Long Term
The second fuel correction program is the long
term adaptive memory. In order to maintain correct
emission throughout all operating ranges of the
engine, a cell structure based on engine rpm and load
(MAP) is used.
Ther number of cells varies upon the driving con-
ditions. Two cells are used only during idle, based
upon TPS and Park/Neutral switch inputs. There
may be two other cells used for deceleration, based
on TPS, engine rpm, and vehicle speed. The other
twelve cells represent a manifold pressure and an
rpm range. Six of the cells are high rpm and the
other six are low rpm. Each of these cells has a spe-
cific MAP voltage range Typical Adaptive Memory
Fuel Cells .As the engine enters one of these cells the PCM
looks at the amount of short term correction being
used. Because the goal is to keep short term at 0 (O2
Sensor switching at 0.5 volt), long term will update
in the same direction as short term correction was
moving to bring the short term back to 0. Once short
term is back at 0, this long term correction factor is
stored in memory.
The values stored in long term adaptive memory
are used for all operating conditions, including open
loop and cold starting. However, the updating of the
long term memory occurs after the engine has
exceeded approximately 170É-190É F, with fuel control
in closed loop and two minutes of engine run time.
This is done to prevent any transitional temperature
or start-up compensations from corrupting long term
fuel correction.
Long term adaptive memory can change the pulse-
width by as much as 25%, which means it can correct
for all of short term. It is possible to have a problem
that would drive long term to 25% and short term to
another 25% for a total change of 50% away from
base pulse-width calculation.
TYPICAL ADAPTIVE MEMORY FUEL CELLS
Open
ThrottleOpen
ThrottleOpen
ThrottleOpen
ThrottleOpen
ThrottleOpen
Throttle Idle Decel
Vacuum 20 17 13 9 5 0
Above 1,984
rpm1 3 5 7 9 11 13 Drive 15
Below 1,984
rpm02 4 6 8 1012
Neutral14
MAP volt =0 1.4 2.0 2.6 3.3 3.9
Fuel Correction Diagnostics
There are two fuel correction diagnostic routines:
²Fuel System Rich
²Fuel System Lean
A DTC is set and the MIL is illuminated if the
PCM detects either of these conditions. This is deter-
mined based on total fuel correction, short term
times long term.
PROGRAMMABLE COMMUNICATIONS
INTERFACE (PCI) BUS
DESCRIPTION
The Programmable Communication Interface Mul-
tiplex system (PCI Bus) consist of a single wire. The
Body Control Module (BCM) acts as a splice to con-
nect each module and the Data Link Connector(DLC) together. Each module is wired in parallel to
the data bus through its PCI chip set and uses its
ground as the bus reference. The wiring is a mini-
mum 20 gage wire.
OPERATION
Various modules exchange information through a
communications port called the PCI Bus. The Power-
train Control Module (PCM) transmits the Malfunc-
tion Indicator Lamp (Check Engine) On/Off signal
and engine RPM on the PCI Bus. The PCM receives
the Air Conditioning select input, transaxle gear
position inputs over the PCI Bus. The PCM also
receives the air conditioning evaporator temperature
signal from the PCI Bus.
The following components access or send informa-
tion on the PCI Bus.
RSFUEL INJECTION14-21
FUEL INJECTION (Continued)
ProCarManuals.com
Page 1382 of 2177
SPECIAL TOOLS
FUEL
ACCELERATOR PEDAL
REMOVAL
(1) Hold the throttle body throttle lever in the
wide open position. Remove the throttle cable from
the throttle body cam (Fig. 1).
(2) From inside the vehicle, hold up the pedal and
remove the pedal retainer and throttle cable from the
upper end of the pedal lever (Fig. 2).
(3) Remove nuts from accelerator pedal attaching
studs. Remove assembly from vehicle (Fig. 3).
Pressure Gauge Assembly C±4799±B
Fuel Pressure Test Adapter 6539
Spanner Wrench 6856
Fuel Line Adapter 1/4
O2S (Oxygen Sensor) Remover/InstallerÐC-4907
O2S (Oxygen Sensor) Remover/Installer - 8439
Fig. 1 THROTTLE CABLE RELEASE
RSFUEL INJECTION14-23
FUEL INJECTION (Continued)
ProCarManuals.com