Dodge Durango (DN). Manual — part 273

not remove cables from cap. Remove cable from
spark plug. Connect ohmmeter to spark plug termi-
nal end of cable and to corresponding electrode in
distributor cap. Resistance should be 250 to 1000
Ohms per inch of cable. If not, remove cable from dis-
tributor cap tower and connect ohmmeter to the ter-
minal ends of cable. If resistance is not within
specifications as found in the SPARK PLUG CABLE
RESISTANCE chart, replace the cable. Test all spark
plug cables in this manner.

To test ignition coil-to-distributor cap cable, do not

remove the cable from the cap. Connect ohmmeter to
rotor button (center contact) of distributor cap and
terminal at ignition coil end of cable. If resistance is
not within specifications as found in the Spark Plug
Cable Resistance chart, remove the cable from the
distributor cap. Connect the ohmmeter to the termi-
nal ends of the cable. If resistance is not within spec-
ifications

as

found

in

the

Spark

Plug

Cable

Resistance chart, replace the cable. Inspect the igni-
tion coil tower for cracks, burns or corrosion.

SPARK PLUG CONDITIONS

NORMAL OPERATING

The few deposits present on the spark plug will

probably be light tan or slightly gray in color. This is
evident with most grades of commercial gasoline
(Fig. 13). There will not be evidence of electrode
burning. On all engines except the 4.7L V-8, gap
growth will not average more than approximately
0.025 mm (.001 in) per 3200 km (2000 miles) of oper-
ation. On the 4.7L V-8, gap growth will not average
more than approximately.0015 in per 3200 km (2000
miles) of operation. Spark plugs that have normal
wear can usually be cleaned, have the electrodes
filed, have the gap set and then be installed.

Some fuel refiners in several areas of the United

States have introduced a manganese additive (MMT)
for unleaded fuel. During combustion, fuel with MMT
causes the entire tip of the spark plug to be coated
with a rust colored deposit. This rust color can be
misdiagnosed as being caused by coolant in the com-
bustion chamber. Spark plug performance may be
affected by MMT deposits.

COLD FOULING/CARBON FOULING

Cold fouling is sometimes referred to as carbon

fouling. The deposits that cause cold fouling are basi-

cally carbon (Fig. 13). A dry, black deposit on one or
two plugs in a set may be caused by sticking valves
or defective spark plug cables. Cold (carbon) fouling
of the entire set of spark plugs may be caused by a
clogged air cleaner element or repeated short operat-
ing times (short trips).

WET FOULING OR GAS FOULING

A spark plug coated with excessive wet fuel or oil

is wet fouled. In older engines, worn piston rings,
leaking valve guide seals or excessive cylinder wear
can cause wet fouling. In new or recently overhauled
engines, wet fouling may occur before break-in (nor-
mal oil control) is achieved. This condition can usu-
ally be resolved by cleaning and reinstalling the
fouled plugs.

OIL OR ASH ENCRUSTED

If one or more spark plugs are oil or oil ash

encrusted (Fig. 14), evaluate engine condition for the
cause of oil entry into that particular combustion
chamber.

ELECTRODE GAP BRIDGING

Electrode gap bridging may be traced to loose

deposits in the combustion chamber. These deposits
accumulate on the spark plugs during continuous
stop-and-go driving. When the engine is suddenly
subjected to a high torque load, deposits partially liq-
uefy and bridge the gap between electrodes (Fig. 15).
This short circuits the electrodes. Spark plugs with
electrode gap bridging can be cleaned using standard
procedures.

SPARK PLUG CABLE RESISTANCE

MINIMUM

MAXIMUM

250 Ohms Per Inch

1000 Ohms Per Inch

3000 Ohms Per Foot

12,000 Ohms Per Foot

Fig. 13 Normal Operation and Cold (Carbon) Fouling

1 – NORMAL
2 – DRY BLACK DEPOSITS
3 – COLD (CARBON) FOULING

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IGNITION SYSTEM

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DIAGNOSIS AND TESTING (Continued)

SCAVENGER DEPOSITS

Fuel scavenger deposits may be either white or yel-

low (Fig. 16). They may appear to be harmful, but
this is a normal condition caused by chemical addi-
tives in certain fuels. These additives are designed to
change the chemical nature of deposits and decrease
spark plug misfire tendencies. Notice that accumula-
tion on the ground electrode and shell area may be
heavy, but the deposits are easily removed. Spark
plugs with scavenger deposits can be considered nor-
mal in condition and can be cleaned using standard
procedures.

CHIPPED ELECTRODE INSULATOR

A chipped electrode insulator usually results from

bending the center electrode while adjusting the
spark plug electrode gap. Under certain conditions,
severe detonation can also separate the insulator
from the center electrode (Fig. 17). Spark plugs with
this condition must be replaced.

PREIGNITION DAMAGE

Preignition damage is usually caused by excessive

combustion chamber temperature. The center elec-
trode dissolves first and the ground electrode dis-
solves somewhat latter (Fig. 18). Insulators appear
relatively deposit free. Determine if the spark plug
has the correct heat range rating for the engine.
Determine if ignition timing is over advanced or if

Fig. 14 Oil or Ash Encrusted

Fig. 15 Electrode Gap Bridging

1 – GROUND ELECTRODE
2 – DEPOSITS
3 – CENTER ELECTRODE

Fig. 16 Scavenger Deposits

1 – GROUND ELECTRODE COVERED WITH WHITE OR

YELLOW DEPOSITS

2 – CENTER ELECTRODE

Fig. 17 Chipped Electrode Insulator

1 – GROUND ELECTRODE
2 – CENTER ELECTRODE
3 – CHIPPED INSULATOR

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IGNITION SYSTEM

8D - 9

DIAGNOSIS AND TESTING (Continued)

other operating conditions are causing engine over-
heating. (The heat range rating refers to the operat-
ing temperature of a particular type spark plug.
Spark plugs are designed to operate within specific
temperature ranges. This depends upon the thick-
ness and length of the center electrodes porcelain
insulator.)

SPARK PLUG OVERHEATING

Overheating is indicated by a white or gray center

electrode insulator that also appears blistered (Fig.
19). The increase in electrode gap will be consider-
ably in excess of 0.001 inch per 2000 miles of opera-
tion. This suggests that a plug with a cooler heat
range rating should be used. Over advanced ignition
timing, detonation and cooling system malfunctions
can also cause spark plug overheating.

IGNITION SWITCH AND KEY LOCK CYLINDER

ELECTRICAL DIAGNOSIS

For ignition switch electrical schematics, refer to

Ignition Switch in Group 8W, Wiring Diagrams.

MECHANICAL DIAGNOSIS (KEY DIFFICULT TO
ROTATE)

Vehicles equipped with an automatic trans-

mission and a floor mounted shifter: a cable is
used to connect the interlock device in the steering
column assembly, to the transmission floor shift
lever. This interlock device is used to lock the trans-
mission shifter in the PARK position when the key
lock cylinder is rotated to the LOCKED or ACCES-
SORY position. The interlock device within the steer-
ing column is not serviceable. If repair is necessary,
the steering column assembly must be replaced.
Refer to Group 19, Steering for procedures.

If the ignition key is difficult to rotate to or from

the LOCK or ACCESSORY position, it may not be
the fault of the key cylinder or the steering column
components. The brake transmission shift interlock
cable may be out of adjustment. Refer to Brake
Transmission Shift Interlock Cable Adjustment in
Group 21, Transmissions for adjustment procedures.

Vehicles equipped with an automatic trans-

mission and a steering column mounted shifter:
an interlock device is located within the steering col-
umn. This interlock device is used to lock the trans-
mission shifter in the PARK position when the key
lock cylinder is in the LOCKED or ACCESSORY
position. If it is difficult to rotate the key to or from
the LOCK or ACCESSORY position, the interlock
device within the steering column may be defective.
This device is not serviceable. If repair is necessary,
the steering column assembly must be replaced.
Refer to Group 19, Steering for procedures.

Vehicles equipped with a manual transmis-

sion and a floor mounted shifter: on certain mod-
els, a lever is located on the steering column behind
the ignition key lock cylinder. The lever must be
manually operated to allow rotation of the ignition
key lock cylinder to the LOCK or ACCESSORY posi-
tion. If it is difficult to rotate the key to the LOCK or
ACCESSORY position, the lever mechanism may be
defective. This mechanism is not serviceable. If
repair is necessary, the steering column assembly
must be replaced. Refer to Group 19, Steering for
procedures.

On other models, the ignition key cylinder must be

depressed to allow it to be rotated into the LOCK or
ACCESSORY position. If it is difficult to rotate the
key to the LOCK or ACCESSORY position, the lock
mechanism within the steering column may be defec-
tive. This mechanism is not serviceable. If repair is

Fig. 18 Preignition Damage

1 – GROUND ELECTRODE STARTING TO DISSOLVE
2 – CENTER ELECTRODE DISSOLVED

Fig. 19 Spark Plug Overheating

1 – BLISTERED WHITE OR GRAY COLORED INSULATOR

8D - 10

IGNITION SYSTEM

DN

DIAGNOSIS AND TESTING (Continued)

necessary, the steering column assembly must be
replaced. Refer to Group 19, Steering for procedures.

REMOVAL AND INSTALLATION

SPARK PLUG CABLES

CAUTION: When

disconnecting

a

high

voltage

cable from a spark plug or from the distributor cap,
twist the rubber boot slightly (1/2 turn) to break it
loose (Fig. 20). Grasp the boot (not the cable) and
pull it off with a steady, even force.

Install cables into the proper engine cylinder firing

order (Fig. 21).

When replacing the spark plug and coil cables,

route the cables correctly and secure in the proper
retainers. Failure to route the cables properly can
cause the radio to reproduce ignition noise. It could
also cause cross ignition of the plugs or short circuit
the cables to ground.

When installing new cables, make sure a positive

connection is made. A snap should be felt when a
good connection is made between the plug cable and
the distributor cap tower.

SPARK PLUGS

REMOVAL

On 3.9L V-6 and 5.2/5.9L V-8 engines, spark plug

cable heat shields are pressed into the cylinder head
to surround each cable boot and spark plug (Fig. 22).

If removal of the heat shield(s) is necessary,

remove the spark plug cable and compress the sides
of shield for removal. Each shield is slotted to allow
for compression and removal. To install the shields,
align shield to machined opening in cylinder head
and tap into place with a block of wood.

4.7L V–8 Engine: Each individual spark plug is

located under each ignition coil. Each individual igni-
tion coil must be removed to gain access to each
spark plug. Refer to Ignition Coil Removal/Installa-
tion.

(1) Except 4.7L Engine: Prior to removing spark

plug, spray compressed air around spark plug hole
and area around spark plug. This will help prevent
foreign material from entering combustion chamber.

(2) 4.7L V–8 Engine: Prior to removing spark plug,

spray compressed air around base of ignition coil at
cylinder head. This will help prevent foreign material
from entering combustion chamber.

Fig. 22 Heat Shields—3.9/5.2/5.9L Engines

1 – AIR GAP
2 – SPARK PLUG BOOT HEAT SHIELD

Fig. 20 Cable Removal

1 – SPARK PLUG CABLE AND BOOT
2 – SPARK PLUG BOOT PULLER
3 – TWIST AND PULL
4 – SPARK PLUG

Fig. 21 Engine Firing Order—5.2/5.9L V-8 Engine

DN

IGNITION SYSTEM

8D - 11

DIAGNOSIS AND TESTING (Continued)