exhaust manifold JEEP WRANGLER 1994 Owners Manual

Fig. 2 Oxygen Sensor
Fig. 3 Exhaust Pipe-to-Catalytic Converter
Connection
JEXHAUST SYSTEM AND INTAKE MANIFOLD 11 - 3

Fig. 5 Exhaust Pipe-to-Catalytic Converter
ConnectionÐYJ Vehicles
11 - 4 EXHAUST SYSTEM AND INTAKE MANIFOLDJ

Fig. 7 Rear Exhaust Tailpipe Hanger Clamp
JEXHAUST SYSTEM AND INTAKE MANIFOLD 11 - 5

Fig. 9 Rear Exhaust Tailpipe Hanger/Bracket
11 - 6 EXHAUST SYSTEM AND INTAKE MANIFOLDJ

Fig. 11 Intake/Engine Exhaust Manifold Installation
(2.5L Engine)
JEXHAUST SYSTEM AND INTAKE MANIFOLD 11 - 7

(3) Install new fuel pump outlet hose. Secure with
new clamps.
(4) Connect wire terminals to motor.
(5) Install new fuel pump inlet filter.
INSTALLATIONÐYJ MODELS
(1) Install a new fuel pump inlet filter.
(2) Install fuel pump module assembly with a new
gasket between the assembly and tank. Tighten
mounting screws to 2 Nzm (18 in. lbs.) torque.
(3) Install fuel tank. Refer to Fuel Tank Installa-
tionÐYJ Models.
(4) Fill fuel tank. Install fuel tank cap.
(5) Install negative battery cable.
(6) Start vehicle and check for leaks.
FUEL PUMP ELECTRICAL CONTROL
For an electrical operational description of the fuel
pump, refer to the MFI SystemÐComponent Descrip-
tion/System Operation section of this group. See Au-
tomatic Shut Down (ASD) RelayÐPCM Output.
For the 1994 model year, the ballast resistor and
ballast resistor bypass relay are no longer used to
control the fuel pump circuit.
FUEL PRESSURE RELEASE PROCEDURE
WARNING: THE FUEL SYSTEM IS UNDER CON-
STANT FUEL PRESSURE (EVEN WITH THE ENGINE
OFF) OF APPROXIMATELY 131-269 KPA (19-39
PSI). THIS PRESSURE MUST BE RELEASED BE-
FORE SERVICING ANY FUEL SUPPLY OR FUEL RE-
TURN SYSTEM COMPONENT.
(1) Disconnect negative battery cable.
(2) Remove fuel tank filler neck cap to release fuel
tank pressure.
WARNING: DO NOT ALLOW FUEL TO SPILL ONTO
THE ENGINE INTAKE OR EXHAUST MANIFOLDS.
PLACE SHOP TOWELS UNDER AND AROUND THE
PRESSURE PORT TO ABSORB FUEL WHEN THE
PRESSURE IS RELEASED FROM THE FUEL RAIL.
WARNING: WEAR PROPER EYE PROTECTION
WHEN RELEASING FUEL SYSTEM PRESSURE.
(3) Remove protective cap from pressure test port
on the fuel rail (Fig. 7).
(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.
(6) Place a shop towel under the test port.
(7) To release fuel pressure, screw the other end of
hose onto the fuel pressure test port.(8) After fuel pressure has been released, remove
the hose from the test port.
(9) Install protective cap to fuel test port.
FUEL SYSTEM PRESSURE TEST
The fuel system is equipped with a vacuum as-
sisted fuel pressure regulator (Fig. 8). With engine at
idle speed, system fuel pressure should be approxi-
mately 214 kPa (31 psi) with the vacuum line con-
nected to the regulator. With the vacuum line
disconnected from the regulator, fuel pressure should
be approximately 269 kPa (39 psi). This is 55-69 kPa
(8-10 psi) higher.
(1) Remove the protective cap at the fuel rail (Fig.
7). Connect the 0-414 kPa (0-60 psi) fuel pressure
gauge (from Gauge Set 5069) to test port pressure fit-
ting on fuel rail (Fig. 9).
(2) Note pressure gauge reading. Fuel pressure
should be approximately 214 kPa (31 psi) at idle.
Fig. 7 Pressure Test PortÐTypical
Fig. 8 Fuel Pressure RegulatorÐTypical
JFUEL SYSTEM 14 - 5

FUEL TANKS
INDEX
page page
Fuel Gauge Sending Unit.................. 15
Fuel Tank.............................. 12
Fuel Tank Filler Tube Cap................. 12
Fuel Tank Pressure Relief/Rollover Valve...... 15General Information....................... 12
Heat Shields............................ 12
No-Lead Fuel Tank Filler Tube.............. 12
GENERAL INFORMATION
All vehicles pass a full 360 degree rollover test
without fuel leakage. To accomplish this, fuel and
vapor flow controls are required for all fuel tank con-
nections.
All models are equipped with a pressure relief/roll-
over valve mounted in the top of the fuel pump mod-
ule. The return line from the fuel pump to the fuel
tank contains a one-way check valve.
An evaporative control system prevents raw fuel
vapor from escaping into the atmosphere. Fuel va-
pors from the fuel tank are collected in the EVAP
canister. When the engine is operating, the vapors
are drawn into the intake manifold to be used in
combustion. Refer to Group 25, Emission Control
System for more information.
Inspect all hose/tube connections for completeness.
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
wear that could lead to failure. If it is necessary to
replace a hose, only hose marked EFM/EFI may be
used.
When installing hoses, be sure that they are routed
away from contact with other vehicle components.
The hose clamps used on fuel injected vehicles are
of a special rolled edge construction to prevent the
edge of the clamp from cutting into the hose. Only
these rolled edge type clamps may be used on this
system. Other types of clamps may cut into the hoses
and cause high pressure fuel leaks.
NO-LEAD FUEL TANK FILLER TUBE
All vehicles are designed to operate using Un-
leaded fuels. The diameter of the opening in the fuel
tank filler neck is sized to only accept unleaded fuel
nozzles. Gasoline station pumps for unleaded and
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
with a deflector, which the smaller unleaded nozzle
pushes back upon entering the filler neck. The de-
flector will prevent the larger diameter leaded fuel
nozzles from entering the filler neck and will deflect
fuel away from the filler neck. This happens if filling
of the tank with leaded fuel is attempted.
A label is attached to the instrument panel under
the fuel gauge that reads UNLEADED FUEL ONLY
as a reminder to the driver. A similar label is located
near the fuel tank filler.
FUEL TANK FILLER TUBE CAP
The loss of any fuel or vapor out of the filler neck
is prevented by the use of a safety filler cap. This
will release only under pressure of 10.9 to 13.45 kPa
(1.58 to 1.95 psi). The vacuum release is between .97
and 2.0 kPa (.14 and .29 psi). This cap must be re-
placed by a similar unit if replacement is necessary.
CAUTION: Remove the fuel tank filler tube cap prior
to removing or repairing fuel lines to relieve fuel
tank pressure.
HEAT SHIELDS
The sheet metal heat shields may have to be re-
moved when servicing the fuel tank, fuel lines or va-
por vent line. The heat shields must be installed to
protect the lines and tank from the heat of the ex-
haust system. Refer to Group 11, Exhaust System
and Intake Manifold for proper installation.
FUEL TANK
WARNING: THE FUEL SYSTEM IS UNDER CON-
STANT FUEL PRESSURE (EVEN WITH THE ENGINE
OFF) OF APPROXIMATELY 131-269 KPA (19-39
PSI). THIS PRESSURE MUST BE RELEASED BE-
FORE SERVICING FUEL TANK.
FUEL TANK CAPACITIES
14 - 12 FUEL SYSTEMJ

MULTI-PORT FUEL INJECTION (MFI)ÐCOMPONENT DESCRIPTION/SYSTEM
OPERATION
INDEX
page page
Air Conditioning (A/C) Clutch RelayÐPCM Output.24
Air Conditioning (A/C) ControlsÐPCM Input.... 19
Auto Shut Down (ASD) RelayÐPCM Output.... 24
Automatic Shut Down (ASD) SenseÐPCM Input . 19
Battery VoltageÐPCM Input................ 19
Brake SwitchÐPCM Input.................. 20
Camshaft Position SensorÐPCM Input........ 20
Crankshaft Position SensorÐPCM Input....... 20
Data Link ConnectorÐPCM Input............ 20
Data Link ConnectorÐPCM Output........... 24
EMR LampÐPCM Output.................. 24
Engine Coolant Temperature SensorÐPCM Input . 21
Extended Idle SwitchÐPCM Input............ 21
Fuel InjectorsÐPCM Output................ 25
Fuel Pressure Regulator................... 30
Fuel Pump RelayÐPCM Output............. 25
Fuel Rail............................... 30
General Information....................... 17
Generator FieldÐPCM Output............... 25
Generator LampÐPCM Output.............. 25
Idle Air Control (IAC) MotorÐPCM Output...... 25
Ignition Circuit SenseÐPCM Input............ 21
Ignition CoilÐPCM Output.................. 26Intake Air Temperature SensorÐPCM Input.... 20
Malfunction Indicator LampÐPCM Output...... 26
Manifold Absolute Pressure (MAP) SensorÐ
PCM Input............................ 21
Open Loop/Closed Loop Modes of Operation . . . 27
Overdrive/Override Switch.................. 22
Oxygen (O2S) SensorÐPCM Input........... 22
Park/Neutral SwitchÐPCM Input............. 22
Power Ground........................... 22
Power Steering Pressure SwitchÐPCM Input . . . 22
Powertrain Control Module (PCM)............ 18
Radiator Fan RelayÐPCM Output............ 26
SCI ReceiveÐPCM Input.................. 22
SCI TransmitÐPCM Output................. 26
Sensor ReturnÐPCM Input................. 23
Shift IndicatorÐPCM Output................ 26
Speed ControlÐPCM Input................. 23
Speed ControlÐPCM Output................ 27
TachometerÐPCM Output.................. 27
Throttle Body............................ 29
Throttle Position Sensor (TPS)ÐPCM Input..... 23
Torque Converter Clutch RelayÐPCM Output . . . 27
Vehicle Speed SensorÐPCM Input........... 23
GENERAL INFORMATION
All 2.5L 4 cylinder and 4.0L 6 cylinder engines are
equipped with sequential Multi-Port Fuel Injection
(MFI). The MFI system provides precise air/fuel ra-
tios for all driving conditions.
The Powertrain Control Module (PCM) operates
the fuel system. The PCM was formerly referred to
as the SBEC or engine controller. The PCM is a pre-
programmed, dual microprocessor digital computer.
It regulates ignition timing, air-fuel ratio, emission
control devices, charging system, speed control, air
conditioning compressor clutch engagement and idle
speed. The PCM can adapt its programming to meet
changing operating conditions.
Powertrain Control Module (PCM) Inputsrep-
resent the instantaneous engine operating conditions.
Air-fuel mixture and ignition timing calibrations for
various driving and atmospheric conditions are pre-
programmed into the PCM. The PCM monitors and
analyzes various inputs. It then computes engine fuel
and ignition timing requirements based on these in-
puts. Fuel delivery control and ignition timing will
then be adjusted accordingly.
Other inputs to the PCM are provided by the brake
light switch, air conditioning select switch and the
speed control switches. All inputs to the PCM are
converted into signals.
Electrically operated fuel injectors spray fuel in
precise metered amounts into the intake port directlyabove the intake valve. The injectors are fired in a
specific sequence by the PCM. The PCM maintains
an air/fuel ratio of 14.7 to 1 by constantly adjusting
injector pulse width. Injector pulse width is the
length of time that the injector opens and sprays fuel
into the chamber. The PCM adjusts injector pulse
width by opening and closing the ground path to the
injector.
Manifold absolute pressure (air density) and engine
rpm (speed) are the primary inputs that determine
fuel injector pulse width. The PCM also monitors
other inputs when adjusting air-fuel ratio.
Inputs That Effect Fuel Injector Pulse Width
²Exhaust gas oxygen content
²Engine coolant temperature
²Manifold absolute pressure (MAP)
²Engine speed
²Throttle position
²Battery voltage
²Air conditioning selection
²Transmission gear selection (automatic transmis-
sions only)
²Speed control
The powertrain control module (PCM) adjusts igni-
tion timing by controlling ignition coil operation. The
ignition coil receives battery voltage when the igni-
tion key is in the run or starter position. The PCM
provides a ground for the ignition coil. The coil dis-
JFUEL SYSTEM 14 - 17

OVERDRIVE/OVERRIDE SWITCH
On vehicles equipped with overdrive, the power-
train control module (PCM) regulates the 3-4 over-
drive up-shift and down-shift through the overdrive
solenoid.
Refer to Group 21 for more information.
OXYGEN (O2S) SENSORÐPCM INPUT
The O2S sensor is located in the exhaust down pipe
(Fig. 11). 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
voltage, the sensor acts as a rich-lean switch.
The oxygen sensor is equipped with a heating ele-
ment that keeps the sensor at proper operating tem-
perature during all operating modes. Maintaining
correct sensor temperature at all times allows the
system to enter into closed loop operation sooner.
In Closed Loop operation, the powertrain control
module (PCM) monitors the O2S sensor input (along
with other inputs). It then adjusts the injector pulse
width accordingly. During Open Loop operation, the
PCM ignores the O2S sensor input and adjusts injec-
tor pulse width to a preprogrammed value (based on
other sensor inputs).
PARK/NEUTRAL SWITCHÐPCM INPUT
The park/neutral switch is located on the transmis-
sion housing and provides an input to the powertrain
control module (PCM). This will indicate that the au-
tomatic transmission is in Park, Neutral or a drivegear selection. This input is used to determine idle
speed (varying with gear selection), fuel injector
pulse width and ignition timing advance. Refer to
Group 21, Transmissions, for testing, replacement
and adjustment information.
POWER GROUND
The power ground is used to control ground circuits
for the following powertrain control module (PCM)
loads:
²Generator Field Winding
²8 volt (PCM) power supply
²Fuel Injectors
²Ignition Coil
POWER STEERING PRESSURE SWITCHÐPCM
INPUT
A pressure sensing switch is included in the power
steering system (mounted on the high-pressure line).
This switch will be on vehicles equipped with a 2.5L
engine and power steering. The switch (Fig. 12 YJ
Models or Fig. 13 XJ Models) provides an input to
the PCM. This input is provided during periods of
high pump load and low engine rpm; such as during
parking maneuvers. The PCM will then increase the
idle speed through the idle air control (IAC) motor.
This is done to prevent the engine from stalling un-
der the increased load.
When steering pump pressure exceeds 1896 kPa6
172 kPa (275625 psi) the PCM will increase the en-
gine idle speed. This will prevent the engine from
stalling.
SCI RECEIVEÐPCM 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.
Fig. 11 Heated Oxygen Sensor LocationÐTypical
Fig. 12 Power Steering Pump Pressure SwitchÐYJ
Models
14 - 22 FUEL SYSTEMJ

REMOVAL
(1) Disconnect the electrical connector from the
IAC motor.
(2) Remove IAC motor torx head mounting bolts.
(3) Remove IAC motor.
INSTALLATION
(1) Install IAC motor into throttle body and
tighten retaining bolts.
(2) Connect electrical connector to IAC motor.
IGNITION COIL
Refer to Group 8D, Ignition Systems for removal/
installation procedures.
INTAKE MANIFOLD
Refer to Group 11, Exhaust System and Intake
Manifold for removal/installation procedures.
MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR
The MAP sensor is located on the dash panel near
the rear of the engine cylinder head (valve) cover
(Fig. 9).
REMOVAL
(1) Disconnect the MAP sensor electrical connector
(Fig. 9).
(2) Disconnect the MAP sensor vacuum supply
hose (Fig. 9).
(3) Remove the MAP sensor mounting bolts and
remove MAP sensor.
INSTALLATION
(1) Install MAP sensor to dash panel and secure
with mounting bolts.
(2) Install the MAP sensor vacuum supply hose.
(3) Connect the MAP sensor electrical connector.
OXYGEN (O2S) SENSOR
The O2S sensor is installed in the exhaust down
pipe just below the exhaust manifold flange (Fig. 10).
REMOVAL
WARNING: THE EXHAUST MANIFOLD BECOMES
VERY HOT DURING ENGINE OPERATION. ALLOW
ENGINE TO COOL BEFORE REMOVING OXYGEN
SENSOR.
(1) Raise and support the vehicle.
(2) Separate the electrical connectors.
(3) Remove the O2S sensor from the exhaust man-
ifold. Snap-On oxygen sensor wrench (number YA
8875) may be used for removal and installation.
INSTALLATION
Threads of new factory oxygen sensors are coated
with anti-seize compound to aid in removal.
(1) Install the O2S sensor into the exhaust mani-
fold and tighten to 30 Nzm (22 ft. lbs.) torque.
(2) Connect the O2S sensor wire connector to the
main harness.
Fig. 8 Idle Air Control
MotorÐRemoval/InstallationÐTypical
Fig. 9 MAP SensorÐTypical
Fig. 10 Oxygen SensorÐTypical
JFUEL SYSTEM 14 - 57