1994 JEEP WRANGLER Spark plug

(4) Inspect ignition coil connections. Verify that
coil secondary cable is firmly connected to coil (Figs.
5or6).(5) Verify that distributor cap is correctly attached
to distributor. Be sure that spark plug cables are
firmly connected to the distributor cap and the spark
plugs in their correct firing order. Be sure that coil
cable is firmly connected to distributor cap and coil.
Be sure that camshaft position sensor wire connector
is firmly connected to harness connector (Figs. 7 or
8). Inspect spark plug condition. Refer to Group 8D,
Ignition System. Connect vehicle to an oscilloscope
and inspect spark events for fouled or damaged spark
plugs or cables.
(6) Verify that generator output wire, generator
connector and ground wire are firmly connected to
the generator (Fig. 9).
(7) Inspect the system ground connections at the
cylinder block behind the engine oil dipstick tube
(Fig. 10).
Fig. 4 PDCÐXJ Models
Fig. 5 Ignition CoilÐ2.5L Engine
Fig. 6 Ignition CoilÐ4.0L Engine
Fig. 7 Distributor and WiringÐ2.5L Engine
Fig. 8 Distributor and WiringÐ4.0L Engine
JFUEL SYSTEM 14 - 33

87 and 30. Continuity should not be present between
terminals number 87A and 30.
(8) Disconnect jumper wires from relay and 12
Volt power source.
If continuity or resistance tests did not pass, re-
place relay. If tests passed, refer to Group 8W, Wir-
ing Diagrams for additional circuit information. Also
refer to the appropriate Powertrain Diagnostic Proce-
dures manual for operation of the DRB scan tool.
STARTER MOTOR RELAY TEST
Refer to Group 8A, Battery/Starting/Charging/Sys-
tem Diagnostics, for starter motor relay testing.
INJECTOR TEST
Disconnect the injector wire connector from the in-
jector. Place an ohmmeter on the injector terminals.
Resistance reading should be approximately 14.5
ohms61.2 ohms at 20ÉC (68ÉF). Proceed to following
Injector Diagnosis chart.
FUEL SYSTEM PRESSURE TEST
Refer to the Fuel Delivery System section of this
group. See Fuel System Pressure Test.
ON-BOARD DIAGNOSTICS (OBD)
The Powertrain Control Module (PCM) has been
programmed to monitor many different circuits of the
fuel injection system. If a problem is sensed in a
monitored circuit often enough to indicate an actual
problem, a Diagnostic Trouble Code (DTC) is stored.
The DTC will be stored in the PCM memory for
eventual display to the service technician. If the
problem is repaired or ceases to exist, the PCM can-
cels the DTC after 51 engine starts.
Certain criteria must be met for a diagnostic trou-
ble code (DTC) to be entered into PCM memory. The
criteria may be a specific range of engine rpm, en-
gine temperature and/or input voltage to the PCM.
It is possible that a DTC for a monitored circuit
may not be entered into memory even though a mal-
function has occurred. This may happen because one
of the DTC criteria for the circuit has not been met.
Example: assume that one of the criteria for the
MAP sensor circuit is that the engine must be oper-
ating between 750 and 2000 rpm to be monitored for
a DTC. If the MAP sensor output circuit shorts to
ground when the engine rpm is above 2400 rpm, a 0
volt input will be seen by the PCM. A DTC will not
be entered into memory because the condition does
not occur within the specified rpm range.
A DTC indicates that the powertrain control mod-
ule (PCM) has recognized an abnormal signal in a
circuit or the system. A DTC may indicate the result
of a failure, but never identify the failed component
directly.There are several operating conditions that the
PCM does not monitor and set a DTC for. Refer to
the following Monitored Circuits and Non-Monitored
Circuits in this section.
MONITORED CIRCUITS
The powertrain control module (PCM) can detect
certain problems in the fuel injection system.
Open or Shorted Circuit- The PCM can deter-
mine if sensor output (which is the input to PCM) is
within proper range. It also determines if the circuit
is open or shorted.
Output Device Current Flow- The PCM senses
whether the output devices are hooked up.
If there is a problem with the circuit, the PCM
senses whether the circuit is open, shorted to ground
(-), or shorted to (+) voltage.
Oxygen Sensor- The PCM can determine if the
oxygen sensor is switching between rich and lean.
This is, once the system has entered Closed Loop. Re-
fer to Open Loop/Closed Loop Modes Of Operation in
the Component Description/System Operation section
for an explanation of Closed (or Open) Loop opera-
tion.
NON-MONITORED CIRCUITS
The PCM does not monitor the following circuits,
systems or conditions that could have malfunctions
that result in driveability problems. A Diagnostic
Trouble Code (DTC) may not be displayed for these
conditions.
Fuel Pressure: Fuel pressure is controlled by the
vacuum assisted fuel pressure regulator. The PCM
cannot detect a clogged fuel pump inlet filter, clogged
in-line fuel filter, or a pinched fuel supply or return
line. However, these could result in a rich or lean
condition causing an oxygen sensor DTC to be stored
in the PCM.
Secondary Ignition Circuit: The PCM cannot
detect an inoperative ignition coil, fouled or worn
spark plugs, ignition cross firing, or open circuited
spark plug cables.
Engine Timing: The PCM cannot detect an incor-
rectly indexed timing chain, camshaft sprocket or
crankshaft sprocket. The PCM also cannot detect an
incorrectly indexed distributor. However, these could
result in a rich or lean condition causing an oxygen
sensor DTC to be stored in the PCM.
Cylinder Compression: The PCM cannot detect
uneven, low, or high engine cylinder compression.
Exhaust System: The PCM cannot detect a
plugged, restricted or leaking exhaust system.
Fuel Injector Malfunctions: The PCM cannot de-
termine if the fuel injector is clogged, or the wrong
injector is installed. However, these could result in a
rich or lean condition causing an oxygen sensor DTC
to be stored in the PCM.
14 - 48 FUEL SYSTEMJ

(4) Inspect ignition coil connections. Verify that
coil secondary cable is firmly connected to coil (Figs.
5or6).(5) Verify that distributor cap is correctly attached
to distributor. Be sure that spark plug cables are
firmly connected to the distributor cap and the spark
plugs in their correct firing order. Be sure that coil
cable is firmly connected to distributor cap and coil.
Be sure that camshaft position sensor wire connector
is firmly connected to harness connector (Figs. 7 or
8). Inspect spark plug condition. Refer to Group 8D,
Ignition System. Connect vehicle to an oscilloscope
and inspect spark events for fouled or damaged spark
plugs or cables.
(6) Verify that generator output wire, generator
connector and ground wire are firmly connected to
the generator (Fig. 9).
(7) Inspect the system ground connections at the
cylinder block behind the engine oil dipstick tube
(Fig. 10).
Fig. 4 PDCÐXJ Models
Fig. 5 Ignition CoilÐ2.5L Engine
Fig. 6 Ignition CoilÐ4.0L Engine
Fig. 7 Distributor and WiringÐ2.5L Engine
Fig. 8 Distributor and WiringÐ4.0L Engine
JFUEL SYSTEM 14 - 33

87 and 30. Continuity should not be present between
terminals number 87A and 30.
(8) Disconnect jumper wires from relay and 12
Volt power source.
If continuity or resistance tests did not pass, re-
place relay. If tests passed, refer to Group 8W, Wir-
ing Diagrams for additional circuit information. Also
refer to the appropriate Powertrain Diagnostic Proce-
dures manual for operation of the DRB scan tool.
STARTER MOTOR RELAY TEST
Refer to Group 8A, Battery/Starting/Charging/Sys-
tem Diagnostics, for starter motor relay testing.
INJECTOR TEST
Disconnect the injector wire connector from the in-
jector. Place an ohmmeter on the injector terminals.
Resistance reading should be approximately 14.5
ohms61.2 ohms at 20ÉC (68ÉF). Proceed to following
Injector Diagnosis chart.
FUEL SYSTEM PRESSURE TEST
Refer to the Fuel Delivery System section of this
group. See Fuel System Pressure Test.
ON-BOARD DIAGNOSTICS (OBD)
The Powertrain Control Module (PCM) has been
programmed to monitor many different circuits of the
fuel injection system. If a problem is sensed in a
monitored circuit often enough to indicate an actual
problem, a Diagnostic Trouble Code (DTC) is stored.
The DTC will be stored in the PCM memory for
eventual display to the service technician. If the
problem is repaired or ceases to exist, the PCM can-
cels the DTC after 51 engine starts.
Certain criteria must be met for a diagnostic trou-
ble code (DTC) to be entered into PCM memory. The
criteria may be a specific range of engine rpm, en-
gine temperature and/or input voltage to the PCM.
It is possible that a DTC for a monitored circuit
may not be entered into memory even though a mal-
function has occurred. This may happen because one
of the DTC criteria for the circuit has not been met.
Example: assume that one of the criteria for the
MAP sensor circuit is that the engine must be oper-
ating between 750 and 2000 rpm to be monitored for
a DTC. If the MAP sensor output circuit shorts to
ground when the engine rpm is above 2400 rpm, a 0
volt input will be seen by the PCM. A DTC will not
be entered into memory because the condition does
not occur within the specified rpm range.
A DTC indicates that the powertrain control mod-
ule (PCM) has recognized an abnormal signal in a
circuit or the system. A DTC may indicate the result
of a failure, but never identify the failed component
directly.There are several operating conditions that the
PCM does not monitor and set a DTC for. Refer to
the following Monitored Circuits and Non-Monitored
Circuits in this section.
MONITORED CIRCUITS
The powertrain control module (PCM) can detect
certain problems in the fuel injection system.
Open or Shorted Circuit- The PCM can deter-
mine if sensor output (which is the input to PCM) is
within proper range. It also determines if the circuit
is open or shorted.
Output Device Current Flow- The PCM senses
whether the output devices are hooked up.
If there is a problem with the circuit, the PCM
senses whether the circuit is open, shorted to ground
(-), or shorted to (+) voltage.
Oxygen Sensor- The PCM can determine if the
oxygen sensor is switching between rich and lean.
This is, once the system has entered Closed Loop. Re-
fer to Open Loop/Closed Loop Modes Of Operation in
the Component Description/System Operation section
for an explanation of Closed (or Open) Loop opera-
tion.
NON-MONITORED CIRCUITS
The PCM does not monitor the following circuits,
systems or conditions that could have malfunctions
that result in driveability problems. A Diagnostic
Trouble Code (DTC) may not be displayed for these
conditions.
Fuel Pressure: Fuel pressure is controlled by the
vacuum assisted fuel pressure regulator. The PCM
cannot detect a clogged fuel pump inlet filter, clogged
in-line fuel filter, or a pinched fuel supply or return
line. However, these could result in a rich or lean
condition causing an oxygen sensor DTC to be stored
in the PCM.
Secondary Ignition Circuit: The PCM cannot
detect an inoperative ignition coil, fouled or worn
spark plugs, ignition cross firing, or open circuited
spark plug cables.
Engine Timing: The PCM cannot detect an incor-
rectly indexed timing chain, camshaft sprocket or
crankshaft sprocket. The PCM also cannot detect an
incorrectly indexed distributor. However, these could
result in a rich or lean condition causing an oxygen
sensor DTC to be stored in the PCM.
Cylinder Compression: The PCM cannot detect
uneven, low, or high engine cylinder compression.
Exhaust System: The PCM cannot detect a
plugged, restricted or leaking exhaust system.
Fuel Injector Malfunctions: The PCM cannot de-
termine if the fuel injector is clogged, or the wrong
injector is installed. However, these could result in a
rich or lean condition causing an oxygen sensor DTC
to be stored in the PCM.
14 - 48 FUEL SYSTEMJ

Fig. 27 Chipped Electrode Insulator
Fig. 28 Preignition Damage
Fig. 29 Spark Plug Overheating
JIGNITION SYSTEMS 8D - 17

Fig. 10 Spark Plug Cable PositionsÐ2.5L Engine
Fig. 12 Distributor InstallationÐ2.5L Engine
8D - 24 IGNITION SYSTEMSJ