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Jeep XJ. Manual - part 336

Refer to Fuel Filter/Fuel Pressure Regulator in this
group for information.

The fuel rail is not repairable.

FUEL TANK FILLER TUBE CAP

DESCRIPTION

The plastic fuel tank filler tube cap is threaded

onto the end of the fuel fill tube. Certain models are
equipped with a 1/4 turn cap.

OPERATION

The loss of any fuel or vapor out of fuel filler tube

is prevented by the use of a pressure-vacuum fuel fill
cap. Relief valves inside the cap will release fuel tank
pressure at predetermined pressures. Fuel tank vac-
uum will also be released at predetermined values.
This cap must be replaced by a similar unit if
replacement is necessary. This is in order for the sys-
tem to remain effective.

CAUTION: Remove fill cap before servicing any fuel
system component to relieve tank pressure. If
equipped with a California emissions package and a
Leak Detection Pump (LDP), the cap must be tight-
ened securely. If cap is left loose, a Diagnostic
Trouble Code (DTC) may be set.

FUEL TUBES/LINES/HOSES AND CLAMPS

DESCRIPTION

Also refer to Quick-Connect Fittings.

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.

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.

If equipped: The hose clamps used to secure rub-

ber hoses on fuel injected vehicles are of a special
rolled edge construction. 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 hoses and cause high-pressure fuel leaks.

Use new original equipment type hose clamps.

QUICK-CONNECT FITTINGS

DESCRIPTION

Different types of quick-connect fittings are used to

attach various fuel system components, lines and
tubes. These are: a single-tab type, a two-tab type or
a plastic retainer ring type. Some are equipped with
safety latch clips. Some may require the use of a spe-
cial tool for disconnection and removal. Refer to
Quick-Connect Fittings Removal/Installation for more
information.

CAUTION: The interior components (o-rings, clips)
of quick-connect fittings are not serviced sepa-
rately, but new plastic spacers are available for
some types. If service parts are not available, do
not attempt to repair the damaged fitting or fuel line
(tube). If repair is necessary, replace the complete
fuel line (tube) assembly.

DIAGNOSIS AND TESTING

FUEL PUMP PRESSURE TEST

Use this test in conjunction with the Fuel Pump

Capacity Test, Fuel Pressure Leak Down Test and
Fuel Pump Amperage Test found elsewhere in this
group.

Check Valve Operation: The electric fuel pump

outlet contains a one-way check valve to prevent fuel
flow back into the tank and to maintain fuel supply
line pressure (engine warm) when pump is not oper-
ational. It is also used to keep the fuel supply line
full of gasoline when pump is not operational. After
the vehicle has cooled down, fuel pressure may drop
to 0 psi (cold fluid contracts), but liquid gasoline will
remain in fuel supply line between the check valve
and

fuel

injectors.

Fuel

pressure

that

has

dropped to 0 psi on a cooled down vehicle
(engine off) is a normal condition. When the elec-
tric fuel pump is activated, fuel pressure should
immediately (1–2 seconds) rise to specification.

All fuel systems are equipped with a fuel tank

module mounted, combination fuel filter/fuel pressure
regulator. The fuel pressure regulator is not con-
trolled by engine vacuum.

WARNING: THE FUEL SYSTEM IS UNDER CON-
STANT FUEL PRESSURE EVEN WITH THE ENGINE
OFF. BEFORE DISCONNECTING FUEL LINE AT
FUEL RAIL, THIS PRESSURE MUST BE RELEASED.
REFER

THE

FUEL

SYSTEM

PRESSURE

RELEASE PROCEDURE.

(1) Remove protective cap at fuel rail test port.

Connect the 0–414 kPa (0-60 psi) fuel pressure gauge

14 - 6

FUEL SYSTEM

DESCRIPTION AND OPERATION (Continued)

(from gauge set 5069) to test port pressure fitting on
fuel rail (Fig. 7). The DRB III Scan Tool along
with the PEP module, the 500 psi pressure
transducer,

and

the

transducer-to-test

port

adapter may also be used in place of the fuel
pressure gauge.

(2) Start and warm engine and note pressure

gauge reading. Fuel pressure should be 339 kPa

6 34

kPa (49.2 psi

6 5 psi) at idle.

(3) If engine runs, but pressure is below 44.2 psi,

check for a kinked fuel supply line somewhere
between fuel rail and fuel pump module. If line is not
kinked, but specifications for either the Fuel Pump
Capacity, Fuel Pump Amperage or Fuel Pressure
Leak Down Tests were not met, replace fuel pump
module

assembly.

Refer

Fuel

Pump

Module

Removal/Installation.

(4) If operating pressure is above 54.2 psi, electric

fuel pump is OK, but fuel pressure regulator is defec-
tive. Replace fuel filter/fuel pressure regulator. Refer
to Fuel Filter/Fuel Pressure Regulator Removal/In-
stallation for more information.

(5) Install protective cap to fuel rail test port.

FUEL PUMP CAPACITY TEST

Before performing this test, verify fuel pump

pressure. Refer to Fuel Pump Pressure Test.
Use this test in conjunction with the Fuel Pres-
sure Leak Down Test.

(1) Release fuel system pressure. Refer to Fuel

Pressure Release Procedure.

(2) Disconnect fuel supply line at fuel rail. Refer to

Quick-Connect Fittings. Some engines may require
air cleaner housing removal before line disconnection.

(3) Obtain correct Fuel Line Pressure Test Adapter

Tool Hose. Tool number 6539 is used for 5/16” fuel
lines and tool number 6631 is used for 3/8” fuel lines.

(4) Connect

correct

Fuel

Line

Pressure

Test

Adapter Tool Hose into disconnected fuel supply line.
Insert other end of Adaptor Tool Hose into a gradu-
ated container.

(5) Remove fuel fill cap.
(6) To activate fuel pump and pressurize system,

obtain DRB scan tool and actuate ASD Fuel System
Test.

(7) A good fuel pump will deliver at least 1/4 liter

of fuel in 7 seconds. Do not operate fuel pump for
longer than 7 seconds with fuel line disconnected as
fuel pump module reservoir may run empty.

(a) If capacity is lower than specification, but

fuel pump can be heard operating through fuel fill
cap opening, check for a kinked/damaged fuel sup-
ply line somewhere between fuel rail and fuel
pump module.

(b) If line is not kinked/damaged, and fuel pres-

sure is OK, but capacity is low, replace fuel filter/
fuel pressure regulator. The filter/regulator may be
serviced separately on certain applications. Refer
to Fuel Filter/Fuel Pressure Regulator Removal/In-
stallation for additional information.

replace fuel pump module assembly. Refer to Fuel
Pump Module Removal/Installation.

FUEL PRESSURE LEAK DOWN TEST

Use this test in conjunction with the Fuel Pump

Pressure Test and Fuel Pump Capacity Test.

Check Valve Operation: The electric fuel pump

fuel

injectors.

Fuel

pressure

that

has

dropped to 0 psi on a cooled down vehicle
(engine off) is a normal condition. When the elec-
tric fuel pump is activated, fuel pressure should
immediately (1–2 seconds) rise to specification.

Abnormally long periods of cranking to restart a

hot engine that has been shut down for a short
period of time may be caused by:

• Fuel pressure bleeding past a fuel injector(s).

• Fuel pressure bleeding past the check valve in

the fuel pump module.

(1) Disconnect the fuel inlet line at fuel rail. Refer

to Fuel Tubes/Lines/Hoses and Clamps in this section
of the group for procedures. On some engines, air

Fig. 7 Fuel Pressure Test Gauge (Typical Gauge

Installation at Test Port)

1 – SERVICE (TEST) PORT
2 – FUEL PRESSURE TEST GAUGE
3 – FUEL RAIL

FUEL SYSTEM

14 - 7

DIAGNOSIS AND TESTING (Continued)

cleaner housing removal may be necessary before
fuel line disconnection.

(2) Obtain correct Fuel Line Pressure Test Adapter

Tool Hose. Tool number 6539 is used for 5/16” fuel
lines and tool number 6631 is used for 3/8” fuel lines.

(3) Connect

correct

Fuel

Line

Pressure

Test

Adapter Tool Hose between disconnected fuel line
and fuel rail (Fig. 8).

(4) Connect the 0-414 kPa (0-60 psi) fuel pressure

test gauge (from Gauge Set 5069) to the test port on
the appropriate Adaptor Tool. The DRB III Scan
Tool along with the PEP module, the 500 psi
pressure transducer, and the transducer-to-test
port adapter may also be used in place of the
fuel pressure gauge.

The fittings on both tools must be in good

condition and free from any small leaks before
performing the proceeding test.

(5) Start engine and bring to normal operating

temperature.

(6) Observe test gauge. Normal operating pressure

should be 339 kPa

6 34 kPa (49.2 psi 6 5 psi).

(7) Shut engine off.
(8) Pressure should not fall below 30 psi for five

minutes.

(9) If pressure falls below 30 psi, it must be deter-

mined if a fuel injector, the check valve within the
fuel pump module, or a fuel tube/line is leaking.

(10) Again, start engine and bring to normal oper-

ating temperature.

(11) Shut engine off.
(12) Testing for fuel injector or fuel rail leak-

age: Clamp off the rubber hose portion of Adaptor
Tool between the fuel rail and the test port “T” on
Adapter Tool. If pressure now holds at or above 30
psi, a fuel injector or the fuel rail is leaking.

(13) Testing for fuel pump check valve, filter/

regulator check valve or fuel tube/line leakage:
Clamp off the rubber hose portion of Adaptor Tool
between the vehicle fuel line and test port “T” on
Adapter Tool. If pressure now holds at or above 30
psi, a leak may be found at a fuel tube/line. If no
leaks are found at fuel tubes or lines, one of the
check valves in either the electric fuel pump or filter/
regulator may be leaking.

Note: A quick loss of pressure usually indicates a

defective check valve in the filter/regulator. A slow
loss of pressure usually indicates a defective check
valve in the electric fuel pump.

The electric fuel pump is not serviced separately.

Replace the fuel pump module assembly. The filter/
regulator may be replaced separately on certain
applications. Refer to Fuel Filter/Fuel Pressure Reg-
ulator Removal/Installation for additional informa-
tion.

FUEL PUMP AMPERAGE TEST

This amperage (current draw) test is to be done in

conjunction with the Fuel Pump Pressure Test, Fuel
Pump Capacity Test and Fuel Pressure Leak Down
Test. Before performing the amperage test, be sure
the temperature of the fuel tank is above 50° F (10°
C).

The DRB Scan Tool along with the DRB Low Cur-

rent Shunt (LCS) adapter (Fig. 9) and its test leads
will be used to check fuel pump amperage specifica-
tions.

(1) Be sure fuel tank contains fuel before starting

test. If tank is empty or near empty, amperage read-
ings will be incorrect.

(2) Obtain LCS adapter.
(3) Plug cable from LCS adapter into DRB scan

tool at SET 1 receptacle.

(4) Plug DRB into vehicle 16–way connector (data

link connector).

(5) Connect (-) and (+) test cable leads into LCS

adapter receptacles. Use 10 amp (10A +) receptacle
and common (-) receptacles.

(6) Gain access to MAIN MENU on DRB screen.
(7) Press DVOM button on DRB.

Fig. 8 Connecting Adapter Tool—Typical

1 – VEHICLE FUEL LINE
2 – TEST PORT “T”
3 – SPECIAL TOOL 6923, 6631, 6541 OR 6539
4 – FUEL PRESSURE TEST GAUGE
5 – FUEL LINE CONNECTION AT RAIL
6 – FUEL RAIL

14 - 8

FUEL SYSTEM

DIAGNOSIS AND TESTING (Continued)

(8) Using left/right arrow keys, highlight CHAN-

NEL 1 function on DRB screen.

(9) Press ENTER three times.
(10) Using up/down arrow keys, highlight RANGE

on DRB screen (screen will default to 2 amp scale).

(11) Press ENTER to change 2 amp scale to 10

amp scale. This step must be done to prevent
damage to DRB scan tool or LCS adapter
(blown fuse).

(12) Remove cover from Power Distribution Center

(PDC).

(13) Remove fuel pump relay from PDC. Refer to

label on PDC cover for relay location.

WARNING: BEFORE PROCEEDING TO NEXT STEP,
NOTE THE FUEL PUMP WILL BE ACTIVATED AND
SYSTEM PRESSURE WILL BE PRESENT. THIS WILL
OCCUR AFTER CONNECTING TEST LEADS FROM
LCS ADAPTER INTO FUEL PUMP RELAY CAVITIES.
THE FUEL PUMP WILL OPERATE EVEN WITH IGNI-
TION KEY IN OFF POSITION. BEFORE ATTACHING
TEST LEADS, BE SURE ALL FUEL LINES AND FUEL
SYSTEM COMPONENTS ARE CONNECTED.

CAUTION: TO PREVENT POSSIBLE DAMAGE TO
THE VEHICLE ELECTRICAL SYSTEM AND LCS
ADAPTER, THE TEST LEADS MUST BE CON-
NECTED

INTO

RELAY

CAVITIES

EXACTLY

SHOWN IN FOLLOWING STEPS.

Depending upon vehicle model, year or engine con-

figuration, three different types of relays may be
used: Type-1, type-2 and type–3.

(14) If equipped with type–1 relay (Fig. 10),

attach test leads from LCS adapter into PDC relay
cavities number 30 and 87. For location of these cav-
ities, refer to numbers stamped to bottom of relay
(Fig. 10).

(15) If equipped with type–2 relay (Fig. 11),

attach test leads from LCS adapter into PDC relay
cavities number 30 and 87. For location of these cav-
ities, refer to numbers stamped to bottom of relay
(Fig. 11).

(16) If equipped with type–3 relay (Fig. 12),

attach test leads from LCS adapter into PDC relay
cavities number 3 and 5. For location of these cavi-
ties, refer to numbers stamped to bottom of relay
(Fig. 12).

(17) When LCS adapter test leads are attached

into relay cavities, fuel pump will be activated.
Determine fuel pump amperage on DRB screen.
Amperage should be below 10.0 amps. If amperage is
below 10.0 amps, and specifications for the Fuel
Pump Pressure, Fuel Pump Capacity and Fuel Pres-
sure Leak Down tests were met, the fuel pump mod-
ule is OK.

(18) If amperage is more than 10.0 amps, replace

fuel pump module assembly. The electric fuel pump
is not serviced separately.

(19) Disconnect test leads from relay cavities

immediately after testing.

Fig. 9 Low Current Shunt Adapter

1 – LOW CURRENT SHUNT ADAPTER
2 – PLUG TO DRB
3 – TEST LEAD RECEPTACLES

TERMINAL LEGEND

NUMBER

IDENTIFICATION

COMMON FEED

COIL GROUND

COIL BATTERY

NORMALLY OPEN

87A

NORMALLY CLOSED

Fig. 10 Type–1 Relay

FUEL SYSTEM

14 - 9

DIAGNOSIS AND TESTING (Continued)

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