Jeep 1997 Grand Cherokee Service Manual page 348

8D - 6 IGNITION SYSTEM
DIAGNOSIS AND TESTING (Continued)
COIL (MANUFACTURER)
Diamond
Toyodenso
(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 sys-
tems.
(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 Diagnos-
tics in Group 14, Fuel Systems. Check the Power-
train 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. 8) from the PCM.
Check 32-way connectors for any spread terminals or
corrosion.
Fig. 8 PCM and Three 32–Way Connectors
(3) 32–WAY CONNECTORS PCM
PRIMARY RESISTANCE
21-27°C (70-80°F)
0.97 - 1.18 Ohms
0.95 - 1.20 Ohms
IGNITION COIL RESISTANCE
GROUND ALLIGATOR CLIP THIS CLIP CAPACITOR
SECONDARY RESISTANCE
11,300 - 15,300 Ohms
11,300 - 13,300 Ohms
(6) Remove test lead from the coil positive termi-
nal. Connect an 18 gauge jumper wire between the
battery positive terminal and the coil positive termi-
nal.
(7) Make the special jumper shown in (Fig. 9).
Using the jumper, momentarily ground the ignition
coil driver circuit at the PCM connector (cavity A-7).
For cavity/terminal location of this circuit, refer to
Group 8W, Wiring. A spark should be generated at
the coil cable when the ground is removed.
Fig. 9 Special Jumper Ground-to-Coil
NegativeTerminal
(8) If spark is generated, replace the PCM.
(9) If spark is not seen, use the special jumper to
ground the coil negative terminal directly.
(10) If spark is produced, repair wiring harness for
an open condition.
(11) If spark is not produced, replace the ignition
coil.
DISTRIBUTOR CAP
Remove the distributor cap and wipe it clean with
a dry lint free cloth. Visually inspect the cap for
cracks, carbon paths, broken towers or damaged
rotor button (Fig. 10) or (Fig. 11). Also check for
white deposits on the inside (caused by condensation
entering the cap through cracks). Replace any cap
that displays charred or eroded terminals. The
machined surface of a terminal end (faces toward
rotor) will indicate some evidence of erosion from
normal operation. Examine the terminal ends for evi-
dence of mechanical interference with the rotor tip.
DISTRIBUTOR ROTOR
Visually inspect the rotor (Fig. 12) for cracks, evi-
dence of corrosion or the effects of arcing on the
metal tip. Also check for evidence of mechanical
interference with the cap. Some charring is normal
.33 MF CLIP TO COIL NEG- CONNECT CLIP GROUND MOMENTARILY ATIVE THIS TO NEGATIVE ALLIGATOR COIL THIS
21-27°C (70-80°F)
CLIP
ZG