Jeep Cherokee 1999 Electronic Service Manual page 1272

X J
DESCRI PT I ON AN D OPERAT I ON (Cont inue d)
(A/C) Con t r ols—E CM In pu t for a ddit ion a l in for m a -
t ion .
Th e A/C r ela y is loca t ed in t h e P ower Dist r ibu t ion
Cen t er (P DC). Th e P DC is loca t ed n ext t o t h e ba t t er y
in t h e en gin e com pa r t m en t . F or t h e loca t ion of t h e
r ela y wit h in t h e P DC, r efer t o la bel on P DC cover.
TIMING SOLENOID—ECM OUTPUT
Th e t im in g solen oid is loca t ed on t h e bot t om of t h e
fu el in ject ion pu m p (F ig. 12).
Fig. 12 Timing Solenoid
Th is 12(+) volt , pu lse widt h m odu la t ed (du t y–cycle)
ou t pu t con t r ols t h e a m ou n t of fu el t im in g (a dva n ce)
in t h e fu el in ject ion pu m p. Th e h igh er t h e du t y–cy-
cle, t h e lower t h e a dva n ce. Th e lower t h e du t y–cycle,
t h e m or e a dva n ced t h e fu el t im in g.
Th e du t y–cycle is det er m in ed by t h e E CM fr om
in pu t s it r eceives fr om t h e fu el in ject or sen sor a n d
en gin e speed sen sor.
TACHOMETER—PCM OUTPUT
Th e P CM r ecieves en gin e r pm va lu es fr om t h e
E CM con t r oller, a n d t h en su pplies en gin e r pm va lu es
t o t h e Body Con t r oller t h a t t h en su pplies t h e in st r u -
m en t clu st er m ou n t ed t a ch om et er (if equ ipped). Refer
t o Gr ou p 8E for t a ch om et er in for m a t ion .
GLOW PLUG RELA Y—ECM OUTPUT
Wh en t h e ign it ion (key) swit ch is pla ced in t h e ON
posit ion , a sign a l is sen t t o t h e E CM r ela t in g cu r r en t
en gin e coola n t t em per a t u r e. Th is sign a l is sen t fr om
t h e en gin e coola n t t em per a t u r e sen sor.
Aft er r eceivin g t h is sign a l, t h e E CM will det er m in e
if, wh en a n d for h ow lon g a per iod t h e glow plu g
r ela y sh ou ld be a ct iva t ed. Th is is don e befor e, du r in g
a n d a ft er t h e en gin e is st a r t ed. Wh en ever t h e glow
FUEL SYSTEM—2.5L DIESEL ENGINE
Fig. 13 Glow Plug Relay Location
plu g r ela y is a ct iva t ed, it will con t r ol t h e 12V+ 100
a m p cir cu it for t h e oper a t ion of t h e fou r glow plu gs.
Wit h a cold en gin e, t h e glow plu g r ela y a n d glow
plu gs m a y be a ct iva t ed for a m a xim u m t im e of 200
secon ds. Refer t o t h e followin g Glow P lu g Con t r ol
ch a r t for a t em per a t u r e/t im e com pa r ison of glow plu g
r ela y oper a t ion .
In t h is ch a r t , P r e–H ea t a n d P ost –H ea t t im es a r e
m en t ion ed. P r e–h ea t is t h e a m ou n t of t im e t h e glow
plu g r ela y cir cu it is a ct iva t ed wh en t h e ign it ion (key)
swit ch is ON, bu t t h e en gin e h a s yet t o be st a r t ed.
P ost –h ea t is t h e a m ou n t of t im e t h e glow plu g r ela y
cir cu it is a ct iva t ed a ft er t h e en gin e is oper a t in g. Th e
Glow P lu g la m p will n ot be illu m in a t ed du r in g t h e
post –h ea t cycle.
GLOW PLU G CON T ROL
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