Jeep Cherokee 2000 Service Manual - page 1258
when cold. Do not check the plugs if the engine
has
recently
been
operated.
If
plugs
are
checked when warm, incorrect amp gauge
readings will result.
Use Churchill Glow Plug Tester DX.900 or an
equivalent (Fig. 16) for the following tests. This
tester is equipped with 4 timer lamps.
(1) Remove the glow plugs from the engine. Refer
to Glow Plug Removal/Installation.
(2) Attach the red lead of the tester to the 12V+
(positive) side of the battery.
(3) Attach the black lead of the tester to the 12V–
(negative) side of the battery.
(4) Fit the glow plug into the top of the tester and
secure it with the spring loaded bar (Fig. 16).
(5) Attach the third lead wire of the tester to the
electrical terminal at the end of the glow plug.
(6) When performing the test, the tester button
(Fig. 16) should be held continuously without release
for 20 seconds as indicated by the 4 timer lamps.
Each illuminated lamp represents a 5 second time
lapse.
(a) Press and hold the tester button (Fig. 16)
and note the amp gauge reading. The gauge read-
ing should indicate a momentary, initial current
draw (surge) of approximately 25 amps. After the
initial surge, the amp gauge reading should begin
to fall off. The glow plug tip should start to glow
an orange color after 5 seconds. If the tip did not
glow after 5 seconds, replace the glow plug. Before
discarding the glow plug, check the position of the
circuit breaker on the bottom of the plug tester. It
may have to be reset. Reset if necessary.
(b) Continue to hold the tester button while
observing the amp gauge and the 4 timer lamps.
When all 4 lamps are illuminated, indicating a 20
second time lapse, the amp gauge reading should
indicate a 9–12 amp current draw. If not, replace
the glow plug. Refer to Glow Plug Removal/Instal-
lation.
(7) Check each glow plug in this manner using one
20 second cycle. If the glow plug is to be retested, it
must first be allowed to cool to room temperature.
WARNING: THE
GLOW
PLUG
WILL
BECOME
EXTREMELY
HOT
(GLOWING)
DURING
THESE
TESTS. BURNS COULD RESULT IF IMPROPERLY
HANDLED. ALLOW THE GLOW PLUG TO COOL
BEFORE REMOVING FROM TESTER.
(8) Remove the glow plug from the tester.
SENSOR RESISTANCE (OHMS)
SENSOR RESISTANCE (OHMS)—COOLANT
TEMPERATURE SENSOR/INTAKE AIR
TEMPERATURE SENSOR
TEMPERATURE
RESISTANCE (OHMS)
C
F
MIN
MAX
−40
−40
291,490
381,710
−20
−4
85,850
108,390
−10
14
49,250
61,430
0
32
29,330
35,990
10
50
17,990
21,810
20
68
11,370
13,610
25
77
9,120
10,880
30
86
7,370
8,750
40
104
4,900
5,750
50
122
3,330
3,880
60
140
2,310
2,670
70
158
1,630
1,870
80
176
1,170
1,340
90
194
860
970
100
212
640
270
110
230
480
540
120
248
370
410
Fig. 16 Typical Glow Plug Tester
1 – INSERT GLOW PLUG HERE
2 – OBSERVATION WINDOW
3 – SPRING LOADED BAR
4 – TIMER LAMPS (4)
5 – TEST LEADS
6 – TESTER BUTTON
14 - 32
FUEL SYSTEM—2.5L DIESEL ENGINE
XJ
DIAGNOSIS AND TESTING (Continued)