Jeep Cherokee 1999, Electronic Service Manual

Page: 1274 / 1948

(OH MS) ch a r t . Repla ce t h e sen sor if it is n ot wit h in
t h e r a n ge of r esist a n ce specified in t h e ch a r t .
(3) Test con t in u it y of t h e wir e h a r n ess. Do t h is
bet ween t h e E CM wir e h a r n ess con n ect or a n d t h e
sen sor con n ect or t er m in a l. Also t est con t in u it y of
wir e h a r n ess t o t h e sen sor con n ect or t er m in a l. Refer
t o Gr ou p 8W for wir in g con n ect or a n d cir cu it r y in for-
m a t ion . Repa ir t h e wir e h a r n ess if a n open cir cu it is
in dica t ed.
(4) Aft er t est s a r e com plet ed, con n ect elect r ica l
con n ect or t o sen sor.
GLOW PLUG TEST
H a r d st a r t in g or a r ou gh idle a ft er st a r t in g m a y be
ca u sed by on e or m or e defect ive glow plu gs. Befor e
t est in g t h e glow plu gs, a t est of t h e glow plu g r ela ys
sh ou ld be per for m ed. Th is will en su r e t h a t 12V+ is
a va ila ble a t t h e plu gs wh en st a r t in g t h e en gin e.
Refer t o t h e Glow P lu g Rela y Test for in for m a t ion .
F or a ccu r a t e t est r esu lt s, t h e glow plu gs sh ou ld be
r em oved fr om t h e en gin e. Th e plu gs m u st be ch ecked
wh en cold.
D o n o t c h e c k th e p lu g s if th e e n g in e
h a s re c e n tly be e n o p e ra te d . If p lu g s a re
c h e c k e d w h e n w a rm , in c o rre c t a m p g a u g e
re a d in g s w ill re s u lt.
Use Ch u r ch ill Glow P lu g Test er DX.900 or a n
equ iva len t (F ig. 16) for t h e followin g t est s. Th is
t est er is equ ipped wit h 4 t im er la m ps.
(1) Rem ove t h e glow plu gs fr om t h e en gin e. Refer
t o Glow P lu g Rem ova l/In st a lla t ion .
(2) At t a ch t h e r ed lea d of t h e t est er t o t h e 12V+
(posit ive) side of t h e ba t t er y.
(3) At t a ch t h e bla ck lea d of t h e t est er t o t h e 12V–
(n ega t ive) side of t h e ba t t er y.
(4) F it t h e glow plu g in t o t h e t op of t h e t est er a n d
secu r e it wit h t h e spr in g loa ded ba r (F ig. 16).
(5) At t a ch t h e t h ir d lea d wir e of t h e t est er t o t h e
elect r ica l t er m in a l a t t h e en d of t h e glow plu g.
(6) Wh en per for m in g t h e t est , t h e t est er bu t t on
(F ig. 16) sh ou ld be h eld con t in u ou sly wit h ou t r elea se
for 20 secon ds a s in dica t ed by t h e 4 t im er la m ps.
E a ch illu m in a t ed la m p r epr esen t s a 5 secon d t im e
la pse.
(a ) P r ess a n d h old t h e t est er bu t t on (F ig. 16)
a n d n ot e t h e a m p ga u ge r ea din g. Th e ga u ge r ea d-
in g sh ou ld in dica t e a m om en t a r y, in it ia l cu r r en t
dr a w (su r ge) of a ppr oxim a t ely 25 a m ps. Aft er t h e
in it ia l su r ge, t h e a m p ga u ge r ea din g sh ou ld begin
t o fa ll off. Th e glow plu g t ip sh ou ld st a r t t o glow
a n or a n ge color a ft er 5 secon ds. If t h e t ip did n ot
glow a ft er 5 secon ds, r epla ce t h e glow plu g. Befor e
disca r din g t h e glow plu g, ch eck t h e posit ion of t h e
cir cu it br ea ker on t h e bot t om of t h e plu g t est er. It
m a y h a ve t o be r eset . Reset if n ecessa r y.
(b) Con t in u e t o h old t h e t est er bu t t on wh ile
obser vin g t h e a m p ga u ge a n d t h e 4 t im er la m ps.
Wh en a ll 4 la m ps a r e illu m in a t ed, in dica t in g a 20
secon d t im e la pse, t h e a m p ga u ge r ea din g sh ou ld
in dica t e a 9–12 a m p cu r r en t dr a w. If n ot , r epla ce
t h e glow plu g. Refer t o Glow P lu g Rem ova l/In st a l-
la t ion .
(7) Ch eck ea ch glow plu g in t h is m a n n er u sin g on e
20 secon d cycle. If t h e glow plu g is t o be r et est ed, it
m u st fir st be a llowed t o cool t o r oom t em per a t u r e.
SEN SOR RESI STAN CE (OH M S)
Fig. 16 Typical Glow Plug Tester
X J FUEL SYSTEM—2.5L DIESEL ENGINE 14 - 31
DI AGN OSI S AN D T EST I N G (Cont inue d)