Jeep 200 Cherokee, Service Manual

Page: 1419 / 2119

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)