Optimize Fuel System Guide

ZJ FUEL SYSTEM 14 - 1

FUEL SYSTEM

CONTENTS

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ACCELERATOR PEDAL AND THROTTLE CABLE MULTI-PORT FUEL INJECTION (MFI)—4.0L 6
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 CYL. ENGINE—GENERAL DIAGNOSIS . . . . . 29
FUEL DELIVERY SYSTEM . . . . . . . . . . . . . . . . . . 3 MULTI-PORT FUEL INJECTION (MFI)—5.2L V-8
FUEL TANKS . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 ENGINE—COMPONENT DESCRIPTION/
GENERAL INFORMATION . . . . . . . . . . . . . . . . . . 1 SYSTEM OPERATION . . . . . . . . . . . . . . . . . . . 53
MULTI-PORT FUEL INJECTION (MFI)—4.0L 6 MULTI-PORT FUEL INJECTION (MFI)—5.2L V-8
CYL. ENGINE—COMPONENT DESCRIPTION/ ENGINE—COMPONENT REMOVAL/
SYSTEM OPERATION . . . . . . . . . . . . . . . . . . . 17 INSTALLATION . . . . . . . . . . . . . . . . . . . . . . . . 85
MULTI-PORT FUEL INJECTION (MFI)—4.0L 6 MULTI-PORT FUEL INJECTION (MFI)—5.2L V-8
CYL. ENGINE—COMPONENT REMOVAL/ ENGINE—GENERAL DIAGNOSIS . . . . . . . . . . 66
INSTALLATION . . . . . . . . . . . . . . . . . . . . . . . . 45 SPECIFICATIONS . . . . . . . . . . . . . . . . . . . . . . . . 95

GENERAL INFORMATION

Throughout this group, references are made to par- tive Control System is found in Group 25, Emission
ticular vehicle models by alphabetical designation or Control Systems.
by the particular vehicle nameplate. A chart showing
a breakdown of the alphabetical designations is in- FUEL USAGE STATEMENT
cluded in the Introduction section at the beginning of Your vehicle was designed to meet all emission reg-
this manual. ulations and provide excellent fuel economy using
The Fuel System consists of: the fuel tank, an high quality unleaded gasoline. Only use unleaded
electric (fuel tank mounted) fuel pump, a fuel pres- gasolines having a minimum posted octane of 87.
sure regulator, fuel filter, sensors, switches and pow- If your vehicle develops occasional light spark
ertrain control module (PCM). It also consists of fuel knock (ping) at low engine speeds, this is not harm-
tubes/lines/hoses, vacuum hoses, throttle body, fuel ful. However, continued heavy knock at high
rail and fuel injectors. speeds can cause damage and should be re-
The Fuel Delivery System consists of: the electric
ported to your dealer immediately. Engine dam-
fuel pump, a frame mounted fuel filter, fuel tubes/
age as a result of heavy knock operation may not be
lines/hoses, fuel rail, fuel injectors and fuel pressure
covered by the new vehicle warranty.
regulator.
In addition to using unleaded gasoline with the
A Fuel Return System is used on all models with
either a 4.0L or 5.2L engine. A separate fuel return proper octane rating, those that contain deter-
line from the engine to the tank is no longer used on gents, corrosion and stability additives are rec-
any 4.0L or 5.2L engine. Excess fuel is returned ommended. Using gasolines that have these
through the fuel pump module and back into the fuel additives will help improve fuel economy, reduce
tank through the fuel pressure regulator. The fuel emissions and maintain vehicle performance.
pressure regulator is located in the fuel tank within Poor quality gasoline can cause problems such
the fuel pump module. as hard starting, stalling and stumble. If you experi-
The Fuel Tank Assembly consists of: the fuel ence these problems, use another brand of gasoline
tank, filler tube, fuel gauge sending unit/electric fuel before considering service for the vehicle.
pump module, a fuel pressure regulator mounted to
the fuel pump module, a pressure relief/rollover valve GASOLINE/OXYGENATE BLENDS
and a pressure-vacuum filler cap. Some fuel suppliers blend unleaded gasoline with
Also to be considered part of the fuel system is the materials that contain oxygen such as alcohol, MTBE
Evaporation Control System. This is designed to and ETBE. The type and amount of oxygenate used
reduce the emission of fuel vapors into the atmo- in the blend is important. The following are generally
sphere. The description and function of the Evapora- used in gasoline blends:

14 - 2 FUEL SYSTEM ZJ

ETHANOL MTBE/ETBE
Ethanol (Ethyl or Grain Alcohol) properly blended, Gasoline and MTBE (Methyl Tertiary Butyl Ether)
is used as a mixture of 10 percent ethanol and 90 blends are a mixture of unleaded gasoline and up to
percent gasoline. Gasoline with ethanol may be 15 percent MTBE. Gasoline and ETBE (Ethyl Ter-
used in your vehicle. tiary Butyl Ether) are blends of gasoline and up to
17 percent ETBE. Gasoline blended with MTBE or
METHANOL ETBE may be used in your vehicle.
CAUTION: DO NOT USE GASOLINES CONTAINING CLEAN AIR GASOLINE
METHANOL. Use of methanol/gasoline blends may re-
Many gasolines are now being blended that con-
sult in starting and driveability problems. In addition,
tribute to cleaner air, especially in those areas of the
damage may be done to critical fuel system compo-
country where air pollution levels are high. These
nents.
new blends provide a cleaner burning fuel and some
Methanol (Methyl or Wood Alcohol) is used in a va- are referred to as Reformulated Gasoline.
riety of concentrations blended with unleaded gaso- In areas of the country where carbon monoxide lev-
line. You may encounter fuels containing 3 percent or els are high, gasolines are being treated with oxygen-
more methanol along with other alcohols called cosol- ated materials such as MTBE, ETBE and ethanol.
vents. Chrysler Corporation supports these efforts toward
Problems that are the result of using methanol/gas- cleaner air and recommends that you use these gaso-
oline blends are not the responsibility of Chrysler lines as they become available.
Corporation. They may not be covered by the vehicle
warranty.

ZJ FUEL DELIVERY SYSTEM 14 - 3

FUEL DELIVERY SYSTEM

INDEX
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Fuel Filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Fuel Pump Module . . . . . . . . . . . . . . . . . . . . . . . . . 3
Fuel Line with Latch Clip . . . . . . . . . . . . . . . . . . . . 10 Fuel System Pressure Release Procedure . . . . . . . . 4
Fuel Pressure Leak Down Test . . . . . . . . . . . . . . . . 6 Fuel System Pressure Test . . . . . . . . . . . . . . . . . . . 5
Fuel Pressure Regulator . . . . . . . . . . . . . . . . . . . . . 4 Fuel Tubes/Lines/Hoses and Clamps . . . . . . . . . . . . 7
Fuel Pump Capacity Test . . . . . . . . . . . . . . . . . . . . 5 Quick-Connect Fittings . . . . . . . . . . . . . . . . . . . . . . 7
Fuel Pump Electrical Control . . . . . . . . . . . . . . . . . . 4

FUEL PUMP MODULE The fuel pump module is not serviceable. If the
The fuel pump module is installed in the top of the electric fuel pump or the fuel pressure regulator
fuel tank (Fig. 1). The fuel pressure regulator is a needs replacement, the complete fuel pump module
part of the fuel pump module assembly and is no must be replaced.
longer mounted to the fuel rail on either engine. The
fuel pump module contains the following components: REMOVAL
• Electric fuel pump WARNING: THE FUEL SYSTEM IS UNDER A CON-
• Fuel pressure regulator STANT PRESSURE EVEN WITH THE ENGINE OFF.
• Fuel pump reservoir BEFORE SERVICING THE FUEL PUMP MODULE,
• In-tank fuel filter THE FUEL SYSTEM PRESSURE MUST BE RE-
• Fuel gauge sending unit LEASED. REFER TO THE FUEL SYSTEM PRES-
• Fuel supply line (tube) connection SURE RELEASE PROCEDURE IN THIS GROUP.

(1) Drain and remove the fuel tank. Refer to Fuel
Tank removal and installation in the Fuel Tank sec-
tion of this group.
(2) The fuel pump module locknut is threaded onto
the fuel tank. Remove the fuel pump module locknut
(Fig. 2). The fuel pump module will spring up from
the fuel tank after the locknut has been removed.

Fig. 1 Fuel Pump Module Location
The fuel pump used on all models is driven by a
permanent magnet 12 volt electric motor that is im-
mersed in the fuel tank. The electrical pump is inte-
gral with the fuel sender unit. The pump/sender
assembly is installed inside the fuel tank.
The fuel pump has a check valve at the outlet end
that consists of a ball held against a seat by force ap-
Fig. 2 Top View of Fuel Pump Module—Typical
plied from a spring. When the pump is operating,
fuel pressure overcomes spring pressure and forces (3) Remove module from fuel tank.
the ball off its seat, allowing fuel to flow. When the
pump is not operating, spring pressure forces the ball INSTALLATION
back against the seat preventing fuel backflow
CAUTION: Whenever the fuel pump module is ser-
through the pump. viced, the rubber gasket must be replaced.

14 - 4 FUEL DELIVERY SYSTEM ZJ

(1) Clean the fuel tank at the module opening.
(2) Using a new gasket on the fuel tank (Fig. 3),
position fuel pump module into opening in fuel tank.
Refer to figure 2 for rotational position.

Fig. 4 Fuel Pressure Regulator Location
Fuel is supplied to the regulator by the electric fuel
pump. The fuel pump also contains a check valve to
maintain some fuel pressure at the fuel injectors
Fig. 3 Rubber Gasket when the engine is not operating. This will help to
start the engine.
(3) Tighten locknut. If fuel pressure at the pressure regulator exceeds
(4) Install fuel tank. Refer to Fuel Tank Installa- 269-283 kPa (39-41 psi), an internal diaphragm
tion in this group. closes and excess fuel pressure is routed back into
the fuel tank through the pressure regulator. A sep-
FUEL PUMP REPLACEMENT
arate fuel return line to the engine is no longer used
The electric fuel pump is not serviceable. If the fuel with any 4.0L or 5.2L engine.
pump needs replacement, the complete fuel pump
module must be replaced. Refer to the previous pro- REMOVAL/INSTALLATION
cedure. The fuel pressure regulator is not serviced sepa-
rately. If the pressure regulator needs replacement,
FUEL GAUGE SENDING UNIT REPLACEMENT the fuel pump module must be replaced. Refer to
The fuel gauge sending unit is not serviceable. If Fuel Pump Module Removal/Installation for proce-
the unit needs replacement, the complete fuel pump dures.
module must be replaced.
FUEL PUMP ELECTRICAL CONTROL
FUEL PRESSURE REGULATOR The powertrain control module (PCM) computer en-
ergizes the fuel pump through the fuel pump relay.
ALL ENGINES Battery voltage is applied to the relay from the igni-
A fuel pressure regulator is used with all engines. tion switch. The coil in the relay is energized when a
It is mounted inside of the fuel pump module (Fig. 4) ground is provided by the PCM. The relay is located
and is suspended in fuel. in the power distribution center (PDC) next to the
The vacuum assisted fuel pressure regulator battery (Fig. 5). For location of relay within the PDC,
located on the fuel rail is no longer used on the refer to label under PDC cover.
4.0L or 5.2L engine. Also refer to either of the MFI System—Component
Fuel Pressure Regulator Operation: The pres- Description/System Operation sections of this group.
sure regulator is a mechanical device that is not con- See Automatic Shutdown (ASD) Relay—PCM Output.
trolled by engine vacuum or by the powertrain
control module (PCM).
FUEL SYSTEM PRESSURE RELEASE PROCEDURE
The regulator is calibrated to maintain a constant WARNING: THE FUEL SYSTEM IS UNDER CON-
pressure at the fuel pump module outlet fitting of STANT FUEL PRESSURE EVEN WITH THE ENGINE
269-283 kPa (39-41 psi). System operating pressure OFF. THIS PRESSURE MUST BE RELEASED BE-
at the fuel injectors, as measured at the fuel rail test FORE SERVICING ANY FUEL SUPPLY SYSTEM
port is 255-283 kPa (39 psi Ϯ 2 psi). The regulator COMPONENT.
contains a diaphragm, calibrated springs and a fuel
return valve. (1) Disconnect negative battery cable.


Fig. 7 Pressure Test Port Location—5.2L Engine
(4) Obtain the fuel pressure gauge/hose assembly
from fuel pressure gauge tool set 5069. Remove the
gauge from the hose.
(5) Place one end of hose (gauge end) into an ap-
proved gasoline container.
Fig. 5 Power Distribution Center
(6) Place a shop towel under the test port.
(2) Remove fuel tank filler neck cap to release fuel (7) To release fuel pressure, screw the other end of
tank pressure. hose onto the fuel pressure test port.
(8) After fuel pressure has been released, remove
WARNING: DO NOT ALLOW FUEL TO SPILL ONTO the hose from the test port.
THE ENGINE INTAKE OR EXHAUST MANIFOLDS. (9) Install protective cap to fuel test port.
PLACE SHOP TOWELS UNDER AND AROUND THE
PRESSURE PORT TO ABSORB FUEL WHEN THE FUEL SYSTEM PRESSURE TEST
PRESSURE IS RELEASED FROM THE FUEL RAIL. The vacuum assisted fuel pressure regulator
located on the fuel rail is no longer used on the
WARNING: WEAR PROPER EYE PROTECTION 4.0L or 5.2L engine.
WHEN RELEASING FUEL SYSTEM PRESSURE. Fuel systems on the 4.0L and 5.2L engines are
equipped with a fuel tank module mounted, fuel
(3) Remove protective cap from pressure test port pressure regulator (Fig. 4). The fuel pressure regula-
on the fuel rail (Figs. 6 or 7). tor is a mechanical device that is not controlled by
the powertrain control module (PCM) or by engine
vacuum.
With engine at idle speed, system fuel pressure
should be 255-283 kPa (39 psi Ϯ 2 psi).
(1) Remove the protective cap at the fuel rail (Figs.
6 or 7). Connect the 0-414 kPa (0-60 psi) fuel pres-
sure gauge (from Gauge Set 5069) to test port pres-
sure fitting on fuel rail (Fig. 8).
(2) Note pressure gauge reading. Fuel pressure
should be 255-283 kPa (39 psi Ϯ 2 psi) at idle.
(3) If pressure is at O psi, connect DRB scan tool
and refer to operating instructions in the appropriate
Powertrain Diagnostics Procedures service manual.
If operating pressure is above 41 psi, the electric
fuel pump is OK, but the fuel pressure regulator if
defective. Replace fuel pump module assembly.

Fig. 6 Pressure Test Port Location—4.0L Engine FUEL PUMP CAPACITY TEST
Before performing this test, verify fuel pump pres-
sure by performing the previous tests.


Fig. 9 Connecting Adapter Tool—Typical
(3) Connect the 0-414 kPa (0-60 psi) fuel pressure
test gauge (from Gauge Set 5069) to the test port on
either tool 6631 or 6539. The fittings on both tools
must be in good condition and free from any
Fig. 8 Typical Fuel Pressure Test Connection small leaks before performing the proceeding
test.
(1) Release the fuel system pressure from fuel sys-
(4) Start engine and bring to normal operating
tem. Refer to the previous Fuel System Pressure Re-
temperature.
lease Procedure in this group.
(5) Observe test gauge. Normal operating pressure
(2) Disconnect the fuel supply line at the fuel rail.
at the fuel rail test port should be 255-283 kPa (39
Refer to Fuel Tubes/Lines/Hoses and Clamps in this
psi Ϯ 2 psi).
section of the group for procedures.
(6) Shut engine off.
(3) Connect Fuel Line Pressure Test Adapter Tool
(7) Pressure should not fall below 24 psi for five
number 6631 (3/8 in.) into the disconnected fuel sup-
minutes.
ply line. Insert the other end of tool 6631 into an ap-
(8) If pressure falls below 24 psi, it must deter-
proved gasoline container.
mined if a fuel injector, the fuel module mounted fuel
(4) To activate the fuel pump and pressurize the
pressure regulator or a fuel tube/line is leaking.
system, obtain the DRB scan tool. Refer to the appro-
(9) Again, start engine and bring to normal operat-
priate Powertrain Diagnostic Procedures service
ing temperature.
manual for DRB operation.
(10) Shut engine off.
(5) A good fuel pump will deliver at least 1 liter of
(11) Checking for fuel injector leakage: Clamp
fuel per minute.
off the rubber hose portion of either tool 6539 or 6631
between the disconnected fuel tube (line) and test
FUEL PRESSURE LEAK DOWN TEST
port inlet. If pressure now holds at or above 24 psi, a
ENGINE OFF fuel injector or the fuel rail is leaking.
Checking for fuel pump module or fuel tube
Abnormally long periods of cranking to restart a
leakage: Clamp off the rubber hose portion of either
hot engine that has been shut down for a short pe-
tool 6539 or 6631 between the fuel rail and test port
riod of time may be caused by:
inlet. If pressure now holds at or above 24 psi, a leak
• Fuel pressure bleeding past a fuel injector(s).
can be found at a fuel tube/line. If no leaks are found
• Fuel pressure bleeding past the check valve in the
at fuel tubes or lines, replace the fuel pump module.
fuel pump module.
(1) Disconnect the fuel inlet line at fuel rail. Refer MECHANICAL MALFUNCTIONS
to Fuel Tubes/Lines/Hoses and Clamps in this section Mechanical malfunctions are more difficult to diag-
of the group for procedures. nose with this system. The powertrain control mod-
(2) Connect Fuel Line Pressure Test Adapter Tool ule (PCM) has been programmed to compensate for
number 6539 (5/16 in.), or Adapter Tool number 6631 some mechanical malfunctions such as incorrect cam
(3/8 in.) between the disconnected fuel line and fuel timing, vacuum leaks, etc. If engine performance
rail (Fig. 9). problems are encountered and diagnostic trouble


codes are not displayed, the problem may be mechan- (1) Place fuel filter in retaining strap with the
ical rather than electronic. marked ends in the correct position.
(2) Install retaining strap bolt. Tighten to 7 N⅐m
FUEL FILTER (66 in. lbs.) torque.
The fuel filter protects the fuel injectors from dirt, (3) Install fuel lines to filter. Refer to Fuel Tubes/
water and other foreign matter. The filter is located Lines/Hoses and Clamps in this group. Also refer to
under the vehicle near the front of fuel tank (Fig. Quick-Connect Fittings in this group for procedures.
10). Replace fuel filter at intervals specified in the (4) Lower vehicle.
Lubrication and Maintenance Schedule chart found (5) Connect negative battery cable.
in Group 0, Lubrication and Maintenance. (6) Start engine and check for leaks.
REMOVAL FUEL TUBES/LINES/HOSES AND CLAMPS
Also refer to the proceeding section on Quick-Con-
WARNING: THE FUEL SYSTEM IS UNDER CON-
nect Fittings.
STANT FUEL PRESSURE EVEN WITH THE ENGINE
OFF. THIS PRESSURE MUST BE RELEASED BE- WARNING: THE FUEL SYSTEM IS UNDER A CON-
FORE SERVICING THE FUEL FILTER. STANT PRESSURE EVEN WITH THE ENGINE OFF.
BEFORE SERVICING ANY FUEL SYSTEM HOSES,
(1) Disconnect negative battery cable. Remove fuel
FITTINGS OR LINES, THE FUEL SYSTEM PRES-
filler cap.
SURE MUST BE RELEASED. REFER TO THE FUEL
(2) Release fuel system pressure. Refer to the pre-
SYSTEM PRESSURE RELEASE PROCEDURE IN
vious Fuel System Pressure Release Procedure in
THIS GROUP.
this section.
(3) Raise and support vehicle. Inspect all hose connections such as clamps, cou-
(4) Place shop towels under fuel filter. plings and fittings to make sure they are secure and
(5) Disconnect fuel lines at filter. Refer to Quick- leaks are not present. The component should be re-
Connect Fittings in this group for procedures. placed immediately if there is any evidence of degra-
dation that could result in failure.
Never attempt to repair a plastic fuel line/tube. Re-
place as necessary.
Avoid contact of any fuel tubes/hoses with other ve-
hicle components that could cause abrasions or scuff-
ing. Be sure that the plastic fuel lines/tubes are
properly routed to prevent pinching and to avoid heat
sources.
The lines/tubes/hoses used on fuel injected vehicles
are of a special construction. This is due to the
higher fuel pressures and the possibility of contami-
nated fuel in this system. If it is necessary to replace
these lines/tubes/hoses, only those marked EFM/EFI
may be used.
The hose clamps used to secure rubber hoses on
fuel injected vehicles are of a special rolled edge con-
struction. This construction is used to prevent the
edge of the clamp from cutting into the hose. Only
these rolled edge type clamps may be used in this
system. All other types of clamps may cut into the
Fig. 10 Fuel Filter hoses and cause high-pressure fuel leaks.
(6) Remove retaining strap mounting bolt (Fig. 10). Use new original equipment type hose clamps.
(7) Remove filter retaining strap (Fig. 10). Tighten hose clamps to 1 N⅐m (15 in. lbs.) torque.
(8) Remove filter from mounting bracket.
QUICK-CONNECT FITTINGS
INSTALLATION Also refer to the previous Fuel Tubes/Lines/Hoses
and Clamps section.
CAUTION: The ends of the fuel filter are marked for Different types of quick-connect fittings are used to
correct installation. Install filter with the end marked attach various fuel system components. These are: a
IN towards fuel tank and the end marked OUT to- single-tab type, a two-tab type or a plastic retainer
wards engine. ring type.


SINGLE-TAB TYPE
This type of fitting is equipped with a single pull
tab (Fig. 11). The tab is removable. After the tab is
removed, the quick-connect fitting can be separated
from the fuel system component.

Fig. 12 Disconnecting Single-Tab Type Fitting

Fig. 11 Single-Tab Type Fitting
CAUTION: The interior components (o-rings, spac-
ers) of this type of quick-connect fitting are not ser-
viced separately, but new pull tabs 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, Fig. 13 Removing Pull Tab
SURE MUST BE RELEASED. REFER TO THE FUEL (7) Disconnect the quick-connect fitting from the
SYSTEM PRESSURE RELEASE PROCEDURE IN fuel system component being serviced.
THIS GROUP. (8) Inspect the quick-connect fitting body and fuel
system component for damage. Replace as necessary.
(9) Prior to connecting the quick-connect fitting to
DISCONNECTION/CONNECTION component being serviced, check condition of fitting
(1) Disconnect negative battery cable from battery. and component. Clean the parts with a lint-free
(2) Perform the fuel pressure release procedure. cloth. Lubricate them with clean engine oil.
Refer to the Fuel System Pressure Release Procedure (10) Insert the quick-connect fitting into the fuel
in this section. tube or fuel system component until the built-on stop
(3) Clean the fitting of any foreign material before on the fuel tube or component rests against back of
disassembly. fitting.
(4) Press the release tab on the side of fitting to re- (11) Obtain a new pull tab. Push the new tab down
lease pull tab (Fig. 11). until it locks into place in the quick-connect fitting.
(12) Verify a locked condition by firmly pulling on
CAUTION: If this release tab is not pressed prior to
fuel tube and fitting.
releasing the pull tab, the pull tab will be damaged.
(13) Connect negative cable to battery.
(5) While pressing the release tab on the side of
(14) Start engine and check for leaks.
the fitting, use a screwdriver to pry up the pull tab
(Fig. 12).
(6) Raise the pull tab until it separates from the
quick-connect fitting (Fig. 13). Discard the old pull
tab.


TWO-TAB TYPE FITTING (5) Inspect the quick-connect fitting body and com-
This type of fitting is equipped with tabs located on ponent for damage. Replace as necessary.
both sides of the fitting (Fig. 14). These tabs are sup-
plied for disconnecting the quick-connect fitting from CAUTION: When the quick-connect fitting was dis-
component being serviced. 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.

component being serviced, check condition of fitting
and component. Clean the parts with a lint-free
cloth. Lubricate them with clean engine oil.
(7) Insert the quick-connect fitting to the compo-
nent being serviced and into the plastic retainer.
When a connection is made, a click will be heard.
(9) Connect negative cable to battery.
Fig. 14 Typical Two-Tab Type Quick-Connect Fitting (10) Start engine and check for leaks.
CAUTION: The interior components (o-rings, spac- PLASTIC RETAINER RING TYPE FITTING
ers) of this type of quick-connect fitting are not ser- This type of fitting can be identified by the use of a
viced separately, but new plastic retainers are full-round plastic retainer ring (Fig. 15) usually black
available. Do not attempt to repair damaged fittings in color.
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.
THIS GROUP.

DISCONNECTION/CONNECTION
(1) Disconnect negative battery cable from the bat-
tery.
(2) Perform the fuel pressure release procedure.
Refer to the Fuel System Pressure Release Procedure
in this section.
(3) Clean the fitting of any foreign material before
disassembly.
(4) To disconnect the quick-connect fitting, squeeze
the plastic retainer tabs against the sides of the
Fig. 15 Plastic Retainer Ring Type Fitting
quick-connect fitting with your fingers. Tool use is
not required for removal and may damage plastic re- CAUTION: The interior components (o-rings, spac-
tainer. Pull the fitting from the fuel system compo- ers, retainers) of this type of quick-connect fitting
nent being serviced. The plastic retainer will remain are not serviced separately. Do not attempt to repair
on the component being serviced after fitting is dis- damaged fittings or fuel lines/tubes. If repair is nec-
connected. The o-rings and spacer will remain in the essary, replace the complete fuel tube assembly.
quick-connect fitting connector body.


WARNING: THE FUEL SYSTEM IS UNDER A CON- (4) Pry up on the latch clip with a screwdriver
STANT PRESSURE EVEN WITH THE ENGINE OFF. (Fig. 17).
THIS GROUP.

DISCONNECTION/CONNECTION
(1) Disconnect negative battery cable from the bat-
tery.
(2) Perform the fuel pressure release procedure.
in this section.
(3) Clean the fitting of any foreign material before
disassembly.
(4) To release the fuel system component from the
quick-connect fitting, firmly push the fitting towards
Fig. 16 Latch Clip Location—Typical
the component being serviced while firmly pushing
the plastic retainer ring into the fitting (Fig. 15).
With the plastic ring depressed, pull the fitting from
the component. The plastic retainer ring must be
pressed squarely into the fitting body. If this re-
tainer is cocked during removal, it may be dif-
ficult to disconnect fitting. Use an open-end
wrench on the shoulder of the plastic retainer
ring to aid in disconnection.
After disconnection, the plastic retainer ring will
remain with the quick-connect fitting connector body.
(5) Inspect fitting connector body, plastic retainer
ring and fuel system component for damage. Replace
as necessary.
component being serviced, check condition of fitting
and component. Clean the parts with a lint-free
cloth. Lubricate them with clean engine oil. Fig. 17 Latch Clip Removal—Typical
(7) Insert the quick-connect fitting into the compo-
nent being serviced until a click is felt.
(9) Connect negative battery cable to battery.
(10) Start engine and check for leaks.

FUEL LINE WITH LATCH CLIP
DISCONNECTION/CONNECTION AT FUEL RAIL
A latch clip is used to secure the fuel line to the
fuel rail on the 5.2L V-8 engine (Fig. 16). A special
tool will be necessary to separate the fuel line from
the fuel rail after the latch clip is removed.
(1) Disconnect the negative battery cable from bat-
tery.
(2) Perform the fuel pressure release procedure. Fig. 18 Fuel Line Disconnection—Typical
in this section. (5) Slide the latch clip toward the fuel rail while
(3) Clean the fitting of any foreign material before lifting with the screwdriver.
disassembly. (6) Remove the latch clip from fuel rail.


(7) Insert special fuel line removal tool (Snap-On (11) Insert the fuel line onto the fuel rail until a
number FIH 9055-1 or equivalent) into the fuel line click is felt.
(Fig. 18). Use this tool to release the locking fingers (12) Verify a locked condition by firmly pulling on
in the end of the line. fuel line and fitting (15-30 lbs.).
(8) With the special tool still inserted, pull the fuel (13) Install latch clip (snaps into position). If the
line from the fuel rail. latch clip will not fit, this indicates the fuel line
After disconnection, the locking fingers will remain is not properly installed to the fuel rail. Re-
within the quick-connect fitting at the end of the fuel check the fuel line connection.
line. (14) Connect negative battery cable to battery.
(9) Inspect fuel line fitting, locking fingers and fuel (15) Start engine and check for leaks.
rail fitting for damage. Replace as necessary.
(10) Prior to connecting the fuel line to the fuel
rail, check condition of both fittings. Clean the parts
with a lint-free cloth. Lubricate them with clean en-
gine oil.

14 - 12 FUEL TANKS ZJ

FUEL TANKS

INDEX
page page

Fuel Gauge Sending Unit . . . . . .. . . . . . . . . . . . . 14 Fuel Tank Pressure Relief/Rollover Valve . . . . . . . . 14
Fuel Pump—Removal/Installation . . . . . . . . . . . . . 14 General Information . . . . . . . . . . . . . . . . . . . . . . . 12
Fuel Tank . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . 12 Heat Shields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Fuel Tank Capacities . . . . . . . . . .. . . . . . . . . . . . . 12 No-Lead Fuel Tank Filler Tube . . . . . . . . . . . . . . . . 12
Fuel Tank Filler Tube Cap . . . . . .. . . . . . . . . . . . . 12

GENERAL INFORMATION A label is attached to the instrument panel under
These vehicles pass a full 360 degree rollover test the fuel gauge that reads UNLEADED FUEL ONLY
without fuel leakage. To accomplish this, fuel and va- as a reminder to the driver. A similar label is located
por flow controls are required for all fuel tank con- near the fuel tank filler.
nections.
All models are equipped with a pressure relief/roll- FUEL TANK FILLER TUBE CAP
over valve mounted in the top of the fuel pump mod- The loss of any fuel or vapor out of the filler neck
ule. is prevented by the use of a safety filler cap. This
An evaporative control system prevents raw fuel will release only under pressure of 10.9 to 13.45 kPa
vapor from escaping into the atmosphere. Fuel va- (1.58 to 1.95 psi). The vacuum release is between .97
pors from the fuel tank are collected in the EVAP and 2.0 kPa (.14 and .29 psi). This cap must be re-
canister. When the engine is operating, the vapors placed by a similar unit if replacement is necessary.
are drawn into the intake manifold to be used in
combustion. Refer to Group 25, Emission Control CAUTION: Remove fuel tank filler tube cap prior to
System for more information. removing or repairing fuel lines to relieve fuel tank
Inspect all hose/tube connections for completeness. pressure.
Be sure that leaks are not present. Replace any hose
that is cracked, scuffed, swelled, has rubbed against
other vehicle components or shows any other sign of HEAT SHIELDS
wear that could lead to failure. If it is necessary to The sheet metal heat shields may have to be re-
replace a hose, only hose marked EFM/EFI may be moved when servicing the fuel tank, fuel lines or va-
used. por vent line. The heat shields must be installed to
When installing hoses, be sure that they are routed protect the lines and tank from the heat of the ex-
away from contact with other vehicle components. haust system. Refer to Group 11, Exhaust System
The hose clamps used on fuel injected vehicles are and Intake Manifold for proper installation.
of a special rolled edge construction to prevent the
edge of the clamp from cutting into the hose. Only FUEL TANK CAPACITIES
these rolled edge type clamps may be used on this Refer to the Specifications section at the end of the
system. Other types of clamps may cut into the hoses
Fuel System Group.
and cause high-pressure fuel leaks.

NO-LEAD FUEL TANK FILLER TUBE FUEL TANK
These vehicles are designed to operate using Un- WARNING: THE FUEL SYSTEM IS UNDER CON-
leaded fuels. The diameter of the opening in the fuel STANT FUEL PRESSURE EVEN WITH THE ENGINE
tank filler neck is sized to only accept unleaded fuel
OFF. THIS PRESSURE MUST BE RELEASED BE-
nozzles. Gasoline station pumps for unleaded and
FORE SERVICING FUEL TANK.
leaded fuels have different size nozzles. Leaded fuel
nozzles are larger in diameter than unleaded nozzles.
The fuel tank filler neck opening is also equipped REMOVAL
with a deflector, which the smaller unleaded nozzle (1) Disconnect negative battery cable at battery.
pushes back upon entering the filler neck. The deflec- (2) Release fuel system pressure. Refer to the Fuel
tor will prevent the larger diameter leaded fuel noz- System Pressure Release Procedure in the Fuel De-
zles from entering the filler neck and will deflect fuel livery section of this group.
away from the filler neck. This happens if filling of
(3) Raise and support vehicle.
the tank with leaded fuel is attempted.

ZJ FUEL TANKS 14 - 13

(4) Remove the fuel tank filler hose and vent hose
retaining clamps (Fig. 1). Remove both tubes at fuel
filler tube (Fig. 1).

Fig. 1 Fuel Filler Tube and Hoses
(5) Remove the rear tow hooks (if equipped).
(6) Remove the fuel tank skid plate mounting nuts/ Fig. 2 Fuel Tank Mounting
bolts and remove skid plate (Fig. 2) (if equipped). (13) Carefully lower right side of tank while feed-
(7) Remove the optional trailer hitch (if equipped). ing fuel hoses through access hole in body (Fig. 2)
(8) Remove the exhaust tailpipe heat shield mount- until fuel tank filler hose clamps can be removed.
ing bolts and remove shield. (14) Before removing fuel filler hoses (Fig. 2) from
tank, mark their rotational position in relation to
CAUTION: To protect the fuel tank from exhaust tank. Remove both hose clamps and hoses at tank
heat, this shield must reinstalled after tank installa- (Fig. 2). Insert the drain hose (from an approved gas-
tion. oline draining station) into either of the hose open-
ings. Drain tank until empty.
(9) Place a hydraulic jack to bottom of fuel tank. (15) Continue lowering tank and remove from ve-
hicle.
WARNING: PLACE A SHOP TOWEL AROUND FUEL (16) If tank is to be replaced, disconnect fuel tank
LINES TO CATCH ANY EXCESS FUEL. pressure relief/rollover valve (Fig. 2) from tank. For
valve removal, refer to Fuel Tank Pressure Relief/
(10) Disconnect fuel supply line at inlet side of fuel Rollover Valve in this section. Remove fuel pump
filter. Disconnect fuel vent line near front of tank. module from tank. Refer to Fuel Pump Module Re-
Refer to Fuel Tubes/Lines/Hoses and Clamps in this moval/Installation in the Fuel Delivery section of this
group. Also refer to Quick-Connect Fittings for proce- group.
dures.
(11) Disconnect fuel pump module electrical con- INSTALLATION
nector near front of tank. (1) Install fuel pump module and pressure relief/
rollover valve to tank (if removed).
CAUTION: The right (passenger side) of the fuel (2) Connect the fuel filter-to-fuel pump module
tank must be lowered first to gain access to the two supply line to the fuel pump module. Refer to Fuel
fuel filler hose clamps located on the left side of Tubes/Lines/Hoses and Clamps in this group. Also re-
tank (Fig. 2). fer to Quick-Connect Fittings for procedures.
(3) Install fuel filler hoses and hose clamps (Fig. 2)
(12) Remove the two fuel tank strap nuts (Fig. 2). to tank noting their previously marked position.
Position both tank support straps away from tank. (4) Position fuel tank to hydraulic jack.

14 - 14 FUEL TANKS ZJ

(5) Raise tank into position while guiding the fuel
filler hoses into and through the access hole (Fig. 2)
in body.
(6) Continue raising tank until positioned to body.
(7) Attach two fuel tank mounting straps and
mounting nuts.

CAUTION: The two mounting nuts must be tight-
ened until 80 mm (3.149 in.) is attained between the
end of the mounting bolt and bottom of strap. See
insert (Fig. 2). Do not over tighten nuts.

(8) Connect pump module electrical connector.
(9) Install exhaust tailpipe heat shield.
(10) Connect the fuel filter-to-fuel pump module
supply line to the fuel filter. Refer to Fuel Tubes/
Lines/Hoses and Clamps in this group. Also refer to Fig. 3 Pressure Relief/Rollover Valve Location
Quick-Connect Fittings for procedures.
(11) Install the fuel tank skid plate (Fig. 2) and
trailer hitch (if equipped).
(12) Install the rear tow hooks (if equipped).
(13) Install the fuel tank filler hose and vent hose
to tank necks. Tighten both retaining clamps (Fig. 1).
(14) Lower vehicle and connect battery cable to
battery.

FUEL PUMP—REMOVAL/INSTALLATION
The electric fuel pump is not serviceable. If it
needs replacement, the complete fuel pump module
must be replaced. Refer to Fuel Pump Module in the
Fuel Delivery System section of this group.

FUEL GAUGE SENDING UNIT
The fuel gauge sending unit is not serviceable. If it
needs replacement, the complete fuel pump module
must be replaced. Refer to Fuel Pump Module in the
Fuel Delivery System section of this group.

FUEL TANK PRESSURE RELIEF/ROLLOVER VALVE
The fuel tank is equipped with a pressure relief/ Fig. 4 Pressure Relief/Rollover Valve Operation
rollover valve (Fig. 3). The dual function valve will REMOVAL
relieve fuel tank pressure and prevent fuel flow (1) Disconnect negative battery cable.
through the fuel tank vent tubes in the event of ac- (2) Drain and remove the fuel tank. Refer to Fuel
cidental vehicle rollover. Tank removal and installation in the Fuel Tank sec-
The valve consists of a plunger, spring and orifice/ tion of this group.
guide plate (Fig. 4). The valve is normally open al- (3) The valve is seated in a grommet. Remove by
lowing fuel vapor to vent to the EVAP canister. Here prying one side upward and then roll the grommet
it is stored until it can be consumed by the engine out of tank.
(under controlled conditions). The plunger seats in
the guide plate at the orifice preventing liquid fuel INSTALLATION
from reaching the EVAP canister. This is done if bot- (1) Start one side of grommet into opening in fuel
tom of plunger is contacted by fuel sloshing in tank tank. Using finger pressure only, press valve/grom-
when vehicle is cornering. met into place.
In the event of accidental vehicle rollover, the valve (2) Install fuel tank. Refer to Fuel Tank Installa-
is inverted. In this position the plunger is forced tion.
against the guide plate and raw fuel is prevented (3) Fill fuel tank. Install fuel tank filler cap.
from flowing through the valve orifice into the fuel (4) Connect negative battery cable.
tank vent tube. (5) Start vehicle and check for leaks.

ZJ ACCELERATOR PEDAL AND THROTTLE CABLE 14 - 15

ACCELERATOR PEDAL AND THROTTLE CABLE

GENERAL INFORMATION INSTALLATION
The accelerator pedal is connected to the throttle (1) Place accelerator pedal assembly over studs
body linkage by the throttle cable. The cable is pro- protruding from floor pan. Tighten mounting nuts to
tected by a plastic sheathing and is connected to the 10 N⅐m (92 in. lbs.) torque.
throttle body linkage by a ball socket (4.0L engine) or (2) Slide throttle cable into opening in top of pedal
pin (5.2L engine). It is connected to the accelerator arm. Push plastic cable retainer (clip) into pedal arm
pedal arm by a plastic retainer (clip) (Fig. 1). This re- opening until it snaps into place.
tainer (clip) snaps into the top of the accelerator (3) Before starting engine, operate accelerator
pedal arm. Retainer tabs (built into the cable sheath- pedal to check for any binding.
ing) (Fig. 1) fasten the cable to the dash panel.
THROTTLE CABLE
REMOVAL
(1) From inside the vehicle, hold up accelerator
pedal. Remove plastic cable retainer (clip) and throt-
tle cable core wire from upper end of pedal arm (Fig.
1). Plastic cable retainer (clip) snaps into pedal arm.
(2) Remove the cable core wire at pedal arm.
(3) From inside the vehicle, pinch both sides of the
cable housing retainer tabs (Fig. 1) at the dash
panel. Remove cable housing from dash panel and
pull into the engine compartment.
(4) 4.0L Engine: Remove cable from clip on engine
valve cover (Fig. 2) and clip at dash panel.

Fig. 1 Accelerator Pedal Mounting—Typical
Dual throttle return springs (attached to the throt-
tle shaft) are used to close the throttle.

CAUTION: Never attempt to remove or alter these
springs.

ACCELERATOR PEDAL
CAUTION: Be careful not to damage or kink the ca-
ble core wire (within the cable sheathing) while ser-
vicing accelerator pedal or throttle cable.

Fig. 2 Throttle Cable—4.0L Engine
REMOVAL
(1) From inside the vehicle, hold up accelerator (5) Remove the throttle cable ball end socket at
pedal. Remove plastic cable retainer (clip) and throt- throttle body linkage (Figs. 2 or 3) (snaps off).
tle cable core wire from upper end of pedal arm (Fig. (6) 4.0L Engine: Remove throttle cable from throt-
1). Plastic cable retainer (clip) snaps into pedal arm. tle body mounting bracket by compressing retainer
(2) Remove accelerator pedal bracket nuts. Remove tabs and pushing cable through hole in bracket. Re-
accelerator pedal assembly (Fig. 1). move throttle cable from vehicle.

14 - 16 ACCELERATOR PEDAL AND THROTTLE CABLE ZJ

Fig. 3 Throttle Cable—5.2L V-8 Engine Fig. 4 Cable Release Tab—5.2L Engines—Typical
(7) 5.2L Engine: Remove cable housing at throttle (2) 5.2L Engine: Connect cable ball end to throttle
body mounting bracket by pressing forward on re- body linkage ball (snaps on). Connect cable to throt-
lease tab with a small screwdriver (Fig. 4). To pre- tle body bracket (push down and lock).
vent cable housing breakage, press on the tab (3) 4.0L Engine: Snap cable into clip on engine
only enough to release the cable from the valve cover and clip at dash panel.
bracket. Lift the cable housing straight up from (4) Push other end of cable through opening in
bracket while pressing on release tab. Remove throt- dash panel until retaining tabs lock into panel.
tle cable from vehicle. (5) From inside drivers compartment, slide throttle
INSTALLATION cable core wire into opening in top of pedal arm.
(1) 4.0L Engine: Slide throttle cable through hole Push cable retainer (clip) into pedal arm opening un-
in throttle body bracket until retainer tabs lock into til it snaps in place.
bracket. Connect cable ball end to throttle body link- (6) Before starting engine, operate accelerator
age ball (snaps on). pedal to check for any binding.

ZJ FUEL SYSTEM COMPONENT DESCRIPTION/SYSTEM OPERATION—4.0L 6 CYL. ENGINE 14 - 17

MULTI-PORT FUEL INJECTION (MFI)—4.0L 6 CYL. ENGINE—COMPONENT
DESCRIPTION/SYSTEM OPERATION

INDEX
page page

Air Conditioning (A/C) Clutch Relay—PCM Output . 23 Intake Manifold Air Temperature Sensor—PCM
Air Conditioning (A/C) Controls—PCM Input . . . . . . 19 Input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Auto Shutdown (ASD) Relay—PCM Output . . . . . . 23 Malfunction Indicator Lamp—PCM Output . . . . . . . 24
Automatic Shutdown (ASD) Sense—PCM Input . . . 19 Manifold Absolute Pressure (MAP) Sensor—PCM
Battery Voltage—PCM Input . . . . . . . . . . . . . . . . . 19 Input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Brake Switch—PCM Input . . . . . . . . . . . . . . . . . . . 19 Open Loop/Closed Loop Modes of Operation . . . . . 25
Camshaft Position Sensor—PCM Input . . . . . . . . . 19 Oxygen (O2S) Sensor—PCM Input . . . . . . . . . . . . 21
Crankshaft Position Sensor—PCM Input . . . . . . . . 20 Park/Neutral Switch—PCM Input . . . . . . . . . . . . . . 21
Data Link Connector—PCM Input . . . . . . . . . . . . . 19 Power Ground . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Data Link Connector—PCM Output . . . . . . . . . . . . 24 Powertrain Control Module (PCM) . . . . . . . . . . . . . 18
Duty Cycle Evap Purge Solenoid—PCM Output . . . 24
Engine Coolant Temperature Sensor—PCM Input . 21 SCI Receive—PCM Input . . . . . . . . . . . . . . . . . . . 22
Fuel Injectors—PCM Output . . . . . . . . . . . . . . . . . 24 SCI Transmit—PCM Output . . . . . . . . . . . . . . . . . . 25
Fuel Pressure Regulator . . . . . . . . . . . . . . . . . . . . 28 Sensor Return—PCM Input . . . . . . . . . . . . . . . . . . 22
Fuel Rail . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 Shift Indicator—PCM Output . . . . . . . . . . . . . . . . . 25
General Information . . . . . . . . . . . . . . . . . . . . . . . 17 Speed Control—PCM Input . . . . . . . . . . . . . . . . . . 22
Generator Field—PCM Output . . . . . . . . . . . . . . . . 24 Speed Control—PCM Output . . . . . . . . . . . . . . . . . 25
Generator Lamp—PCM Output . . . . . . . . . . . . . . . 24 Tachometer—PCM Output . . . . . . . . . . . . . . . . . . . 25
Idle Air Control (IAC) Motor—PCM Output . . . . . . . 23 Throttle Body . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Ignition Circuit Sense—PCM Input . . . . . . . . . . . . . 21 Throttle Position Sensor (TPS)—PCM Input . . . . . . 22
Ignition Coil—PCM Output . . . . . . . . . . . . . . . . . . . 25 Vehicle Speed Sensor—PCM Input . . . . . . . . . . . . 22

GENERAL INFORMATION specific sequence by the PCM. The PCM maintains
All 4.0L engines are equipped with sequential an air/fuel ratio of 14.7 to 1 by constantly adjusting
Multi-Port Fuel Injection (MFI). The MFI system injector pulse width. Injector pulse width is the
provides precise air/fuel ratios for all driving condi- length of time that the injector opens and sprays fuel
tions. into the chamber. The PCM adjusts injector pulse
The powertrain control module (PCM) operates the width by opening and closing the ground path to the
fuel system. The PCM was formerly referred to as injector.
the SBEC or engine controller. The PCM is a pre-pro- Manifold absolute pressure (air density) and engine
grammed, dual microprocessor digital computer. It rpm (speed) are the primary inputs that determine
regulates ignition timing, air-fuel ratio, emission con- fuel injector pulse width. The PCM also monitors
trol devices, charging system, speed control, air con- other inputs when adjusting air-fuel ratio.
ditioning compressor clutch engagement and idle Inputs That Effect Fuel Injector Pulse Width:
speed. The PCM can adapt its programming to meet • Exhaust gas oxygen content
changing operating conditions. • Engine coolant temperature
Powertrain Control Module (PCM) Inputs rep- • Manifold absolute pressure (MAP)
resent the instantaneous engine operating conditions. • Engine speed
Air-fuel mixture and ignition timing calibrations for • Throttle position
various driving and atmospheric conditions are pre- • Battery voltage
programmed into the PCM. The PCM monitors and • Air conditioning selection
analyzes various inputs. It then computes engine fuel • Transmission gear selection (automatic transmis-
and ignition timing requirements based on these in- sions only)
puts. Fuel delivery control and ignition timing will • Speed control
then be adjusted accordingly. The powertrain control module (PCM) adjusts igni-
Other inputs to the PCM are provided by the brake tion timing by controlling ignition coil operation. The
light switch, air conditioning select switch and the ignition coil receives battery voltage when the igni-
speed control switches. All inputs to the PCM are tion key is in the run or starter position. The PCM
converted into signals. provides a ground for the ignition coil. The coil dis-
Electrically operated fuel injectors spray fuel in charges when the PCM supplies a ground. By switch-
precise metered amounts into the intake port directly ing the ground path on and off, the PCM regulates
above the intake valve. The injectors are fired in a ignition timing.

14 - 18 FUEL SYSTEM COMPONENT DESCRIPTION/SYSTEM OPERATION—4.0L 6 CYL. ENGINE ZJ

The sensors and switches that provide inputs to The PCM adjusts ignition timing based upon in-
the powertrain control module (PCM) comprise the puts it receives from sensors that react to: engine
Engine Control System. It is also comprised of the rpm, manifold absolute pressure, engine coolant tem-
PCM Outputs (engine control devices that the are op- perature, throttle position, transmission gear selec-
erated by the PCM). tion (automatic transmission), vehicle speed and the
brake switch.
SYSTEM DIAGNOSIS The PCM adjusts idle speed based on inputs it re-
The powertrain control module (PCM) tests many ceives from sensors that react to: throttle position,
of its own input and output circuits. If a Diagnostic vehicle speed, transmission gear selection, engine
Trouble Code (DTC) is found in a major system, this coolant temperature and from inputs it receives from
information is stored in the PCM memory. Refer to the air conditioning clutch switch and brake switch.
On-Board Diagnostics in the MFI System—4.0L En- Based on inputs that it receives, the PCM adjusts
gine—General Diagnosis section of this group for ignition coil dwell. The PCM also adjusts the gener-
DTC information. ator charge rate through control of the generator
field and provides speed control operation.
POWERTRAIN CONTROL MODULE (PCM) Powertrain Control Module (PCM) Inputs:
The powertrain control module (PCM) (Fig. 1) oper- • Generator output
ates the fuel system. The PCM was formerly referred • A/C request (if equipped with factory A/C)
to as the SBEC or engine controller. The PCM is a • A/C select (if equipped with factory A/C)
pre-programmed, dual microprocessor digital com- • Auto shutdown (ASD) sense
puter. It regulates ignition timing, air-fuel ratio, • Intake manifold air temperature sensor
emission control devices, charging system, speed con- • Battery voltage
trol, air conditioning compressor clutch engagement • Brake switch
and idle speed. The PCM can adapt its programming • Engine coolant temperature sensor
to meet changing operating conditions. • Crankshaft position sensor
• Ignition circuit sense (ignition switch in run posi-
tion)
• Manifold absolute pressure sensor
• Overdrive/override switch
• Oxygen sensor
• Park/neutral switch (auto. trans. only)
• SCI receive (DRB scan tool connection)
• Speed control resume switch
• Speed control set switch
• Speed control on/off switch
• Camshaft position sensor signal
• Throttle position sensor
• Vehicle speed sensor
• Sensor return
• Power ground
• Signal ground
Powertrain Control Module (PCM) Outputs:
• A/C clutch relay
• Idle air control (IAC) motor
• Auto shutdown (ASD) relay
• Generator field
• Malfunction indicator lamp (Check engine lamp)
Fig. 1 Powertrain Control Module (PCM) • Fuel injectors
• Fuel pump relay
The PCM receives input signals from various • Ignition coil
switches and sensors. Based on these inputs, the • SCI transmit (DRB scan tool connection)
PCM regulates various engine and vehicle operations • Shift indicator lamp (manual transmission only)
through different system components. These compo- • Speed control vacuum solenoid
nents are referred to as powertrain control module • Speed control vent solenoid
(PCM) outputs. The sensors and switches that pro- • Tachometer (on instrument panel, if equipped)
vide inputs to the PCM are considered powertrain The powertrain control module (PCM) contains a
control module (PCM) inputs. voltage convertor. This converts battery voltage to a


regulated 8.0 volts. It is used to power the crankshaft If battery voltage is low, the PCM will increase in-
position sensor, camshaft position sensor and vehicle jector pulse width (period of time that the injector is
speed sensor. The PCM also provides a five (5) volt energized). This is done to compensate for the re-
supply for the manifold absolute pressure (MAP) sen- duced flow through the injector caused by the low-
sor and throttle position sensor (TPS). ered voltage.

AIR CONDITIONING (A/C) CONTROLS—PCM INPUT BRAKE SWITCH—PCM INPUT
The A/C control system information applies to fac- When the brake light switch is activated, the pow-
tory installed air conditioning units. ertrain control module (PCM) receives an input indi-
A/C SELECT SIGNAL: When the A/C switch is in cating that the brakes are being applied. After
the ON position and the A/C low-pressure switch is receiving this input, the PCM maintains idle speed to
closed, an input signal is sent to the powertrain con- a scheduled rpm through control of the idle air con-
trol module (PCM). The signal informs the PCM that trol (IAC) motor. The brake switch input is also used
A/C has been selected. The PCM then adjusts idle to operate the speed control system.
speed to a pre-programmed rpm through the idle air
control (IAC) motor to compensate for increased en- CAMSHAFT POSITION SENSOR—PCM INPUT
gine load. A sync signal is provided by the camshaft position
sensor located in the distributor (Fig. 2). The sync
A/C REQUEST SIGNAL: Once A/C has been se-
signal from this sensor works in conjunction with the
lected, the powertrain control module (PCM) receives
crankshaft position sensor to provide the powertrain
the A/C request signal from the evaporator switch.
control module (PCM) with inputs. This is done to es-
The input indicates that the evaporator temperature
tablish and maintain correct injector firing order.
is in the proper range for A/C application. The PCM Refer to Camshaft Position Sensor in Group 8D, Ig-
uses this input to cycle the A/C compressor clutch nition System for more information.
through the A/C relay. It will also determine the cor-
rect engine idle speed through the idle air control
(IAC) motor position.
If the A/C low-pressure switch opens (indicating a
low refrigerant level), the PCM will not receive an
A/C select signal. The PCM will then remove the
ground from the A/C relay. This will deactivate the
A/C compressor clutch.
If the evaporator switch opens, indicating that
evaporator is not in proper temperature range, the
PCM will not receive the A/C request signal. The
PCM will then remove the ground from the A/C relay,
deactivating the A/C compressor clutch.

AUTOMATIC SHUTDOWN (ASD) SENSE—PCM
INPUT
A 12 volt signal at this input indicates to the PCM
Fig. 2 Camshaft Position Sensor—Typical
that the ASD has been activated. The ASD relay is
located in the power distribution center (PDC) in the DATA LINK CONNECTOR—PCM INPUT
engine compartment. It is used to connect the oxygen The data link connector (diagnostic scan tool con-
sensor heater element, ignition coil, generator field nector) links the DRB scan tool with the powertrain
winding and fuel injectors to 12 volt + power supply. control module (PCM). The data link connector is lo-
This input is used only to sense that the ASD relay cated in the engine compartment (Fig. 3). For opera-
is energized. If the powertrain control module (PCM) tion of the DRB scan tool, refer to the appropriate
does not see 12 volts at this input when the ASD Powertrain Diagnostic Procedures service manual.
should be activated, it will set a Diagnostic Trouble The data link connector uses two different pins on
Code (DTC). the PCM. One is for Data Link Transmit and the
other is for Data Link Receive.
BATTERY VOLTAGE—PCM INPUT
The battery voltage input provides power to the INTAKE MANIFOLD AIR TEMPERATURE SENSOR—
powertrain control module (PCM). It also informs the PCM INPUT
PCM what voltage level is supplied to the ignition The intake manifold air temperature sensor is in-
coil and fuel injectors. stalled in the intake manifold with the sensor ele-


sor signal, is used to differentiate between fuel injec-
tion and spark events. It is also used to synchronize
the fuel injectors with their respective cylinders.
The sensor is bolted to the transmission housing
near the rear of the cylinder head (Figs. 5 or 6).

Fig. 3 Data Link Connector Location—Typical Fig. 5 Crankshaft Position Sensor—4.0L Engine
ment extending into the air stream (Fig. 4). The With Man. Trans.
sensor provides an input voltage to the powertrain
control module (PCM) indicating intake manifold air
temperature. The input is used along with inputs
from other sensors to determine injector pulse width.
As the temperature of the air-fuel stream in the
manifold varies, the sensor resistance changes. This
results in a different input voltage to the PCM.

Fig. 6 Crankshaft Position Sensor—4.0L Engine
Fig. 4 Air Temperature Sensor With Auto. Trans.

CRANKSHAFT POSITION SENSOR—PCM INPUT Refer to Group 8D, Ignition System for more crank-
This sensor is a hall effect device that detects shaft position sensor information.
notches in the flywheel (manual transmission), or The engine will not operate if the PCM does not re-
flexplate (automatic transmission). ceive a crankshaft position sensor input.
This sensor is used to indicate to the powertrain
control module (PCM) that a spark and or fuel injec-
tion event is to be required. The output from this
sensor, in conjunction with the camshaft position sen-


ENGINE COOLANT TEMPERATURE SENSOR—PCM
INPUT
The engine coolant temperature sensor is installed
in the thermostat housing (Fig. 7) and protrudes into
the water jacket. The sensor provides an input volt-
age to the powertrain control module (PCM) relating
engine coolant temperature. The PCM uses this in-
put along with inputs from other sensors to deter-
mine injector pulse width and ignition timing. As
coolant temperature varies, the coolant temperature
sensor’s resistance changes. The change in resistance
results in a different input voltage to the PCM.
When the engine is cold, the PCM will operate in
Open Loop cycle. It will demand slightly richer air-
fuel mixtures and higher idle speeds. This is done
until normal operating temperatures are reached. Fig. 8 Manifold Absolute Pressure (MAP) Sensor
OXYGEN (O2S) SENSOR—PCM INPUT
The O2S sensor is located in the exhaust down pipe
(Fig. 9). It provides an input voltage to the power-
train control module (PCM) relating the oxygen con-
tent of the exhaust gas. The PCM uses this
information to fine tune the air-fuel ratio by adjust-
ing injector pulse width.
The O2S sensor produces voltages from 0 to 1 volt.
This voltage will depend 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 produces a higher voltage. By monitoring
the oxygen content and converting it to electrical
Fig. 7 Coolant Temperature Sensor voltage, the sensor acts as a rich-lean switch.
The oxygen sensor is equipped with a heating ele-
IGNITION CIRCUIT SENSE—PCM INPUT ment that keeps the sensor at proper operating tem-
The ignition circuit sense input tells the powertrain perature during all operating modes. Maintaining
control module (PCM) the ignition switch has ener- correct sensor temperature at all times allows the
gized the ignition circuit. Refer to the wiring dia- system to enter into closed loop operation sooner.
grams for circuit information. In Closed Loop operation, the powertrain control
module (PCM) monitors the O2S sensor input (along
MANIFOLD ABSOLUTE PRESSURE (MAP) with other inputs). It then adjusts the injector pulse
SENSOR—PCM INPUT width accordingly. During Open Loop operation, the
The MAP sensor reacts to absolute pressure in the PCM ignores the O2S sensor input and adjusts injec-
intake manifold. It provides an input voltage to the tor pulse width to a preprogrammed value (based on
powertrain control module (PCM). As engine load other sensor inputs).
changes, manifold pressure varies. The change in
manifold pressure causes MAP sensor voltage to PARK/NEUTRAL SWITCH—PCM INPUT
change. The change in MAP sensor voltage results in The park/neutral switch is located on the transmis-
a different input voltage to the PCM. The input volt- sion housing and provides an input to the powertrain
age level supplies the PCM with information about control module (PCM). This will indicate that the au-
ambient barometric pressure during engine start-up tomatic transmission is in Park, Neutral or a drive
(cranking) and engine load while the engine is run- gear selection. This input is used to determine idle
ning. The PCM uses this input along with inputs speed (varying with gear selection), fuel injector
from other sensors to adjust air-fuel mixture. pulse width, ignition timing advance and vehicle
The MAP sensor is mounted on the dash panel speed control operation. Refer to Group 21, Transmis-
(Fig. 8). The sensor is connected to the throttle body sions, for testing, replacement and adjustment infor-
with a vacuum hose and to the PCM electrically. mation.


THROTTLE POSITION SENSOR (TPS)—PCM INPUT
The throttle position sensor (TPS) is mounted on
the throttle body (Fig. 10). The TPS is a variable re-
sistor that provides the powertrain control module
(PCM) with an input signal (voltage) that represents
throttle blade position. The sensor is connected to the
throttle blade shaft. As the position of the throttle
blade changes, the resistance of the TPS changes.
The PCM supplies approximately 5 volts to the
TPS. The TPS output voltage (input signal to the
PCM) represents the throttle blade position. The
PCM receives an input signal voltage from the TPS.
This will vary in an approximate range of from 1 volt
at minimum throttle opening (idle), to 4 volts at wide
open throttle. Along with inputs from other sensors,
Fig. 9 Heated Oxygen Sensor Location the PCM uses the TPS input to determine current
engine operating conditions. In response to engine
POWER GROUND operating conditions, the PCM will adjust fuel injec-
The power ground is used to control ground circuits tor pulse width and ignition timing.
for the following powertrain control module (PCM)
loads:
• Generator Field Winding
• 8 volt (PCM) power supply
• Fuel Injectors
• Ignition Coil

SCI RECEIVE—PCM INPUT
SCI Receive is the serial data communication re-
ceive circuit for the DRB scan tool. The powertrain
control module (PCM) receives data from the DRB
through the SCI Receive circuit.

SPEED CONTROL—PCM INPUT
The speed control system provides three separate
inputs to the powertrain control module (PCM); On/
Off, Set and Resume. The On/Off input informs the Fig. 10 Throttle Position Sensor and IAC Motor
PCM that the speed control system has been acti-
vated. The Set input informs the PCM that a fixed VEHICLE SPEED SENSOR—PCM INPUT
vehicle speed has been selected. The Resume input The speed sensor (Fig. 11) is located in the exten-
indicates to the PCM that the previous fixed speed is sion housing of the transmission (2WD) or on the
requested. transfer case extension housing (4WD). The sensor
The speed control operating range is from 50 km/h input is used by the powertrain control module
to 142 km/h (35 to 85 mph). Inputs that effect speed (PCM) to determine vehicle speed and distance trav-
control operation are: eled.
• Brake switch position The speed sensor generates 8 pulses per sensor
• Park/neutral switch revolution. These signals, in conjunction with a
• Vehicle speed sensor closed throttle signal from the throttle position sen-
• Throttle position sensor sor, indicate a closed throttle deceleration to the
Refer to Group 8H for further speed control infor- PCM. When the vehicle is stopped at idle, a closed
mation. throttle signal is received by the PCM (but a speed
sensor signal is not received).
SENSOR RETURN—PCM INPUT Under deceleration conditions, the PCM adjusts the
Sensor Return provides a low noise ground refer- idle air control (IAC) motor to maintain a desired
ence for all system sensors. MAP value. Under idle conditions, the PCM adjusts
the IAC motor to maintain a desired engine speed.


When the PCM receives a request for A/C from the
A/C evaporator switch, it will adjust idle air control
(IAC) motor position. This is done to increase idle
speed. The PCM will then activate the A/C clutch
through the A/C clutch relay. The PCM then adjusts
the idle air control (IAC) stepper motor position to
compensate for increased engine load from the A/C
compressor.
By switching the ground path for the relay on and
off, the PCM is able to cycle the A/C compressor
clutch. This is based on changes in engine operating
conditions. If, during A/C operation, the PCM senses
low idle speeds or a wide open throttle condition, it
will de-energize the relay. This prevents A/C clutch
engagement. The relay will remain de-energized until
the idle speed increases or the wide open throttle
condition exceeds 15 seconds, or no longer exists. The
PCM will also de-energize the relay if engine coolant
temperature exceeds 125°C (257°F).

IDLE AIR CONTROL (IAC) MOTOR—PCM OUTPUT
Fig. 11 Vehicle Speed Sensor—Typical The IAC motor is mounted on the throttle body
(Fig. 10) and is controlled by the powertrain control
AIR CONDITIONING (A/C) CLUTCH RELAY—PCM module (PCM).
OUTPUT The throttle body has an air control passage that
The powertrain control module (PCM) activates the provides air for the engine at idle (the throttle plate
A/C compressor through the A/C clutch relay. The is closed). The IAC motor pintle protrudes into the
PCM regulates A/C compressor operation by switch- air control passage and regulates air flow through it.
ing the ground circuit for the A/C clutch relay on and Based on various sensor inputs, the powertrain con-
off. The relay is located in the power distribution trol module (PCM) adjusts engine idle speed by mov-
center (PDC) (Fig. 12). For the location of the relay ing the IAC motor pintle in and out of the air control
within the PDC, refer to label under PDC cover. passage. The IAC motor is positioned when the igni-
tion key is turned to the On position.
A (factory adjusted) set screw is used to mechani-
cally limit the position of the throttle body throttle
plate. Never attempt to adjust the engine idle
speed using this screw. All idle speed functions are
controlled by the PCM.

AUTO SHUTDOWN (ASD) RELAY—PCM OUTPUT
The ASD relay is located in the power distribution
center (PDC) (Fig. 12). For the location of this relay
within the PDC, refer to label under PDC cover.
The ASD supplies battery voltage to the fuel pump,
fuel injector, ignition coil, generator field winding
and oxygen (O2S) sensor heating element. The
ground circuit for the coil in the ASD relay is con-
trolled by the powertrain control module (PCM). The
PCM operates the relay by switching the ground cir-
cuit on and off.
The fuel pump relay is controlled by the PCM
through same circuit that the ASD relay is con-
trolled.
Fig. 12 Power Distribution Center (PDC)

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