Jeep Cherokee 1999 Electronic Service Manual page 1273

14 - 30 FUEL SYSTEM—2.5L DIESEL ENGINE
DESCRI PT I ON AN D OPERAT I ON (Cont inue d)
GLOW PLUGS
Glow plu gs a r e u sed t o h elp st a r t a cold or cool
en gin e. Th e plu g will h ea t u p a n d glow t o h ea t t h e
com bu st ion ch a m ber of ea ch cylin der. An in dividu a l
plu g is u sed for ea ch cylin der. E a ch plu g is t h r ea ded
in t o t h e cylin der h ea d a bove t h e fu el in ject or (F ig.
14).
Fig. 14 Glow Plug
E a ch plu g will m om en t a r ily dr a w a ppr oxim a t ely 25
a m ps of elect r ica l cu r r en t du r in g t h e in it ia l key–on
cycle. Th is is on a cold or cool en gin e. Aft er h ea t in g,
t h e cu r r en t dr a w will dr op t o a ppr oxim a t ely 9–12
a m ps per plu g.
Tot a l m om en t a r y cu r r en t dr a w for a ll fou r plu gs is
a ppr oxim a t ely 100 a m ps on a cold en gin e dr oppin g t o
a t ot a l of a ppr oxim a t ely 40 a m ps a ft er t h e plu gs a r e
h ea t ed.
E lect r ica l oper a t ion of t h e glow plu gs a r e con -
t r olled by t h e glow plu g r ela y. Refer t o t h e pr eviou s
Glow P lu g Rela y—E CM Ou t pu t for a ddit ion a l in for-
m a t ion .
ELECTRIC VACUUM MODULA TOR (EVM)—ECM
OUTPUT
Th is cir cu it con t r ols oper a t ion of t h e E lect r ic Va c-
u u m Modu la t or (E VM). Th e E VM con t r ols oper a t ion
of t h e E GR va lve.
Refer t o Gr ou p 25, E m ission Con t r ol Syst em for
in for m a t ion . See E lect r ic Va cu u m Modu la t or.
DI AGN OSI S AN D T EST I N G
DIESEL DIAGNOSTICS
Th e E CM con t r oller s per for m en gin e off dia gn ost ic
t est s, wh ich m a y be h ea r d for a bou t 60 secon ds a ft er
t u r n in g t h e key off.
ASD RELA Y TEST
To per for m a t est of t h e r ela y a n d it s r ela t ed cir-
cu it r y, r efer t o t h e DRB sca n t ool. To t est t h e r ela y
on ly, r efer t o Rela ys—Oper a t ion /Test in g in t h is sec-
t ion of t h e gr ou p.
D ia g n o s tic Tro u ble Co d e s : Refer t o On -Boa r d
Dia gn ost ics in Gr ou p 25, E m ission Con t r ol Syst em
for a list of Dia gn ost ic Tr ou ble Codes (DTC's) for cer-
t a in fu el syst em com pon en t s.
ENGINE SPEED SENSOR TEST
To per for m a t est of t h e en gin e speed sen sor a n d
it s r ela t ed cir cu it r y, r efer t o t h e DRB sca n t ool.
D ia g n o s tic Tro u ble Co d e s : Refer t o On -Boa r d
Dia gn ost ics in Gr ou p 25, E m ission Con t r ol Syst em
for a list of Dia gn ost ic Tr ou ble Codes (DTC's) for cer-
t a in fu el syst em com pon en t s.
ENGINE COOLANT TEMPERA TURE SENSOR
TEST
Th e sen sor is loca t ed on t h e side of cylin der h ea d
n ea r t h e r ea r of fu el in ject ion pu m p (F ig. 15).
Fig. 15 Engine Coolant Temperature Sensor
F or a list of Dia gn ost ic Tr ou ble Codes (DTC's) for
cer t a in fu el syst em com pon en t s, r efer t o On -Boa r d
Dia gn ost ics in Gr ou p 25, E m ission Con t r ol Syst em .
To t est t h e sen sor on ly, r efer t o t h e followin g:
(1) Discon n ect wir e h a r n ess con n ect or fr om coola n t
t em per a t u r e sen sor.
(2) Test t h e r esist a n ce of t h e sen sor wit h a h igh
in pu t im peda n ce (digit a l) volt –oh m m et er. Th e r esis-
t a n ce (a s m ea su r ed a cr oss t h e sen sor t er m in a ls)
sh ou ld be less t h a n 1340 oh m s wit h t h e en gin e
wa r m . Refer t o t h e followin g Sen sor Resist a n ce
Location
X J