Jeep Cherokee 2000 Service Manual - page 354
SPARK PLUG CABLES
TESTING
Check the spark plug cable connections for good
contact at the coil(s), distributor cap towers, and
spark plugs. Terminals should be fully seated. The
insulators should be in good condition and should fit
tightly on the coil, distributor and spark plugs. Spark
plug cables with insulators that are cracked or torn
must be replaced.
Clean high voltage ignition cables with a cloth
moistened with a non-flammable solvent. Wipe the
cables dry. Check for brittle or cracked insulation.
When testing secondary cables for damage with an
oscilloscope, follow the instructions of the equipment
manufacturer.
If an oscilloscope is not available, spark plug cables
may be tested as follows:
CAUTION: Do not leave any one spark plug cable
disconnected for longer than necessary during test-
ing. This may cause possible heat damage to the
catalytic converter. Total test time must not exceed
ten minutes.
With the engine running, remove spark plug cable
from spark plug (one at a time) and hold next to a
good engine ground. If the cable and spark plug are
in good condition, the engine rpm should drop and
the engine will run poorly. If engine rpm does not
drop, the cable and/or spark plug may not be operat-
ing properly and should be replaced. Also check
engine cylinder compression.
With the engine not running, connect one end of a
test probe to a good ground. Start the engine and run
the other end of the test probe along the entire
length of all spark plug cables. If cables are cracked
or punctured, there will be a noticeable spark jump
from the damaged area to the test probe. The cable
running from the ignition coil to the distributor cap
can be checked in the same manner. Cracked, dam-
aged or faulty cables should be replaced with resis-
tance type cable. This can be identified by the words
ELECTRONIC SUPPRESSION printed on the cable
jacket.
Use an ohmmeter to test for open circuits, excessive
resistance or loose terminals. Remove the distributor
cap from the distributor. Do not remove cables from
cap. Remove cable from spark plug. Connect ohmme-
ter to spark plug terminal end of cable and to corre-
sponding electrode in distributor cap. Resistance
should be 250 to 1000 Ohms per inch of cable. If not,
remove cable from distributor cap tower and connect
ohmmeter to the terminal 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
Fig. 9 Cap Inspection—Internal—Typical
1 – CHARRED OR ERODED TERMINALS
2 – WORN OR DAMAGED ROTOR BUTTON
3 – CARBON PATH
Fig. 10 Rotor Inspection—Typical
1 – INSUFFICIENT SPRING TENSION
2 – CRACKS
3 – EVIDENCE OF PHYSICAL CONTACT WITH CAP
4 – ROTOR TIP CORRODED
SPARK PLUG CABLE RESISTANCE
MINIMUM
MAXIMUM
250 Ohms Per Inch
1000 Ohms Per Inch
3000 Ohms Per Foot
12,000 Ohms Per Foot
XJ
IGNITION SYSTEM
8D - 7
DIAGNOSIS AND TESTING (Continued)