Jeep Cherokee 1999 Electronic Service Manual page 1217

14 - 26 FUEL SYSTEM
DESCRI PT I ON AN D OPERAT I ON (Cont inue d)
ENGINE WARM-UP MODE
Th is is a n Open Loop m ode. Du r in g en gin e wa r m -
u p, t h e power t r a in con t r ol m odu le (P CM) r eceives
in pu t s fr om :
• Ba t t er y volt a ge
• Cr a n ksh a ft posit ion sen sor
• E n gin e coola n t t em per a t u r e sen sor
• In t a ke m a n ifold a ir t em per a t u r e sen sor
• Ma n ifold a bsolu t e pr essu r e (MAP ) sen sor
• Th r ot t le posit ion sen sor (TP S)
• Ca m sh a ft posit ion sen sor sign a l (in t h e dist r ibu t or )
• P a r k/n eu t r a l swit ch (gea r in dica t or sign a l—a u t o.
t r a n s. on ly)
• Air con dit ion in g select sign a l (if equ ipped)
• Air con dit ion in g r equ est sign a l (if equ ipped)
Ba sed on t h ese in pu t s t h e followin g occu r s:
• Volt a ge is a pplied t o t h e fu el in ject or s wit h t h e
ASD r ela y via t h e P CM. Th e P CM will t h en con t r ol
t h e in ject ion sequ en ce a n d in ject or pu lse widt h by
t u r n in g t h e gr ou n d cir cu it t o ea ch in dividu a l in ject or
on a n d off.
• Th e P CM a dju st s en gin e idle speed t h r ou gh t h e
idle a ir con t r ol (IAC) m ot or a n d a dju st s ign it ion t im -
in g.
• Th e P CM oper a t es t h e A/C com pr essor clu t ch
t h r ou gh t h e A/C com pr essor clu t ch r ela y. Th is is don e
if A/C h a s been select ed by t h e veh icle oper a t or a n d
specified pr essu r es a r e m et a t t h e h igh a n d low–pr es-
su r e A/C swit ch es. Refer t o Gr ou p 24, H ea t in g a n d
Air Con dit ion in g for a ddit ion a l in for m a t ion .
• Wh en en gin e h a s r ea ch ed oper a t in g t em per a -
t u r e, t h e P CM will begin m on it or in g O2S sen sor
in pu t . Th e syst em will t h en lea ve t h e wa r m -u p m ode
a n d go in t o closed loop oper a t ion .
IDLE MODE
Wh en t h e en gin e is a t oper a t in g t em per a t u r e, t h is
is a Closed Loop m ode. At idle speed, t h e power t r a in
con t r ol m odu le (P CM) r eceives in pu t s fr om :
• Air con dit ion in g select sign a l (if equ ipped)
• Air con dit ion in g r equ est sign a l (if equ ipped)
• Ba t t er y volt a ge
• Cr a n ksh a ft posit ion sen sor
• E n gin e coola n t t em per a t u r e sen sor
• E xt en ded idle swit ch (4.0L en gin e wit h police
pa cka ge on ly)
• In t a ke m a n ifold a ir t em per a t u r e sen sor
• Ma n ifold a bsolu t e pr essu r e (MAP ) sen sor
• Th r ot t le posit ion sen sor (TP S)
• Ca m sh a ft posit ion sen sor sign a l (in t h e dist r ibu -
t or )
• Ba t t er y volt a ge
• P a r k/n eu t r a l swit ch (gea r in dica t or sign a l—a u t o.
t r a n s. on ly)
• Oxygen sen sor s
• P ower st eer in g pr essu r e swit ch (2.5L en gin e
on ly)
Ba sed on t h ese in pu t s, t h e followin g occu r s:
• Volt a ge is a pplied t o t h e fu el in ject or s wit h t h e
ASD r ela y via t h e P CM. Th e P CM will t h en con t r ol
in ject ion sequ en ce a n d in ject or pu lse widt h by t u r n -
in g t h e gr ou n d cir cu it t o ea ch in dividu a l in ject or on
a n d off.
• Th e P CM m on it or s t h e O2S sen sor in pu t a n d
a dju st s a ir-fu el r a t io by va r yin g in ject or pu lse widt h .
It a lso a dju st s en gin e idle speed t h r ou gh t h e idle a ir
con t r ol (IAC) m ot or.
• Th e P CM a dju st s ign it ion t im in g by in cr ea sin g
a n d decr ea sin g spa r k a dva n ce.
• Th e P CM oper a t es t h e A/C com pr essor clu t ch
t h r ou gh t h e A/C com pr essor clu t ch r ela y. Th is is don e
if A/C h a s been select ed by t h e veh icle oper a t or a n d
specified pr essu r es a r e m et a t t h e h igh a n d low–pr es-
su r e A/C swit ch es. Refer t o Gr ou p 24, H ea t in g a n d
Air Con dit ion in g for a ddit ion a l in for m a t ion .
Th e opt ion a l E xt en ded Idle Swit ch is u sed t o r a ise
a n d h old t h e en gin e idle speed t o a ppr oxim a t ely 1000
r pm . Th is is wh en t h e sh ift er is in eit h er t h e P a r k or
Neu t r a l posit ion a n d t h r ot t le peda l is n ot u sed. A
r ocker-t ype swit ch (ext en ded idle swit ch ) is m ou n t ed
t o t h e in st r u m en t pa n el. Th is swit ch will su pply a
gr ou n d cir cu it (in pu t ) t o t h e power t r a in con t r ol m od-
u le (P CM). Th e s w itc h is a v a ila ble o n ly w ith 4.0L
e n g in e w h e n s u p p lie d w ith o p tio n a l p o lic e
p a c k a g e .
On 2.5L 4–cylin der en gin es, a power st eer in g pr es-
su r e swit ch is u sed t o su pply a n in pu t t o t h e P CM
wh en st eer in g pu m p pr essu r e is h igh . Th is will r a ise
en gin e speed. Refer t o P ower St eer in g P r essu r e
Swit ch in t h is gr ou p for a ddit ion a l in for m a t ion . Th e
4.0L 6–c y lin d e r e n g in e d o e s n o t u s e th is s w itc h .
CRUISE MODE
Wh en t h e en gin e is a t oper a t in g t em per a t u r e, t h is
is a Closed Loop m ode. At cr u isin g speed, t h e power-
t r a in con t r ol m odu le (P CM) r eceives in pu t s fr om :
• Air con dit ion in g select sign a l (if equ ipped)
• Air con dit ion in g r equ est sign a l (if equ ipped)
• Ba t t er y volt a ge
• E n gin e coola n t t em per a t u r e sen sor
• Cr a n ksh a ft posit ion sen sor
• In t a ke m a n ifold a ir t em per a t u r e sen sor
• Ma n ifold a bsolu t e pr essu r e (MAP ) sen sor
• Th r ot t le posit ion sen sor (TP S)
• Ca m sh a ft posit ion sen sor sign a l (in t h e dist r ibu -
t or )
• P a r k/n eu t r a l swit ch (gea r in dica t or sign a l—a u t o.
t r a n s. on ly)
• Oxygen (O2S) sen sor s
Ba sed on t h ese in pu t s, t h e followin g occu r s:
X J