Jeep 1996 Grand Cherokee Service Manual - page 277
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.
(3) Attach one lead of a voltmeter to the positive
(12 volt) jumper wire. Attach the negative side of
voltmeter to a good ground. Determine that sufficient
battery voltage (12.4 volts) is present for the starting
and ignition systems.
(4) Determine that sufficient battery voltage (12.4
volts) is present for the starting and ignition systems.
(5) Crank the engine for 5 seconds while monitor-
ing the voltage at the coil positive terminal:
• If the voltage remains near zero during the entire
period of cranking, refer to On-Board Diagnostics in
Group 14, Fuel Systems. Check the Powertrain Control
Module (PCM) and auto shutdown relay.
• If voltage is at or near battery voltage and drops
to zero after 1-2 seconds of cranking, check the pow-
ertrain control module circuit. Refer to On-Board
Diagnostics in Group 14, Fuel Systems.
• If voltage remains at or near battery voltage during
the entire 5 seconds, turn the key off. Remove the three
32-way connectors (Fig. 9) from the PCM. Check 32-way
connectors for any spread terminals or corrosion.
IGNITION COIL RESISTANCE
Fig. 8 Ignition Coil—Typical (5.2L Shown)
Fig. 9 PCM and Three 32–Way Connectors
8D - 6
IGNITION SYSTEM
ZJ
DIAGNOSIS AND TESTING (Continued)