Jeep 1997 Grand Cherokee Service Manual page 347

CHECK SPARK CABLE FOR SPARK HERE BOOT PLUG AND SPARK PLUG A ENGINE
ZG
DIAGNOSIS AND TESTING (Continued)
Fig. 5 Cable Removal
Fig. 6 Checking for Spark—Typical
ondary coil cable. Refer to Spark Plug Cables in this
group. Also inspect the distributor cap and rotor for
cracks or burn marks. Repair as necessary. If steady
arcing occurs, connect ignition coil cable to the dis-
tributor cap.
(3) Remove a cable from one spark plug.
(4) Using insulated pliers, hold the cable terminal
approximately 12 mm (1/2 in.) from the engine cylin-
der head or block while rotating the engine with the
starter motor. Observe the spark plug cable terminal
for an arc. If steady arcing occurs, it can be expected
that the ignition secondary system is operating cor-
rectly. (If the ignition coil cable is removed for
this test, instead of a spark plug cable, the
spark intensity will be much higher). If steady
arcing occurs at the spark plug cables, but the engine
will not start, connect the DRB scan tool. Refer to
the appropriate Powertrain Diagnostic Procedures
service manual.
GROUND SPARK PLUG BOOT GOOD TWIST AND PULL PULLER IGNITION COIL COIL MOUNT- ING BOLTS IGNITION COIL
IGNITION COIL TEST
To perform a complete test of the ignition coil and
its circuitry, refer to the DRB scan tool. Also refer to
the appropriate Powertrain Diagnostics Procedures
manual. To test the coil only, refer to the following:
The ignition coil (Fig. 7) is designed to operate
without an external ballast resistor.
Fig. 7 Ignition Coil—Typical (5.2L/5.9LShown)
Inspect the ignition coil for arcing. Test the coil
according to coil tester manufacturer's instructions.
Test the coil primary and secondary resistance.
Replace any coil that does not meet specifications.
Refer to the Ignition Coil Resistance chart.
If the ignition coil is being replaced, the secondary
spark plug cable must also be checked. Replace cable
if it has been burned or damaged.
Arcing at the tower will carbonize the cable boot,
which if it is connected to a new ignition coil, will
cause the coil to fail.
If the secondary coil cable shows any signs of dam-
age, it should be replaced with a new cable and new
terminal. Carbon tracking on the old cable can cause
arcing and the failure of a new ignition coil.
FAILURE TO START TEST
To prevent unnecessary diagnostic time and wrong
test results, the Testing For Spark At Coil test
should be performed prior to this test.
WARNING: SET PARKING BRAKE OR BLOCK THE
DRIVE WHEELS BEFORE PROCEEDING WITH THIS
TEST.
(1) Unplug the ignition coil harness connector at
the coil.
(2) Connect a set of small jumper wires (18 gauge
or smaller) between the disconnected harness termi-
nals and the ignition coil terminals. To determine
polarity at connector and coil, refer to the Wiring
Diagrams section.
COIL CONNEC- TOR DRIVE ACCESSORY TENSIONER
IGNITION SYSTEM
BELT
8D - 5