Jeep Cherokee 1999 Electronic Service Manual page 1218

X J
DESCRI PT I ON AN D OPERAT I ON (Cont inue d)
• 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 a dju st
t h e 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. 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 t u r n in g t h e
gr ou n d pa t h t o t h e coil on a n d off.
• 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 clu t ch r ela y. Th is h a ppen s if A/C h a s
been select ed by t h e veh icle oper a t or a n d r equ est ed
by t h e A/C t h er m ost a t .
ACCELERA TION MODE
Th is is a n Open Loop m ode. Th e power t r a in con t r ol
m odu le (P CM) r ecogn izes a n a br u pt in cr ea se in
t h r ot t le posit ion or MAP pr essu r e a s a dem a n d for
in cr ea sed en gin e ou t pu t a n d veh icle a cceler a t ion . Th e
P CM in cr ea ses in ject or pu lse widt h in r espon se t o
in cr ea sed t h r ot t le open in g.
DECELERA TION 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 n Open Loop m ode. Du r in g h a r d deceler a t ion , t h e
power t r a in con t r ol m odu le (P CM) r eceives t h e follow-
in g in pu t s.
• 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)
• Veh icle speed sen sor
If t h e veh icle is u n der h a r d deceler a t ion wit h t h e
pr oper r pm a n d closed t h r ot t le con dit ion s, t h e P CM
will ign or e t h e oxygen sen sor in pu t sign a l. Th e P CM
will en t er a fu el cu t -off st r a t egy in wh ich it will n ot
su pply a gr ou n d t o t h e in ject or s. If a h a r d deceler a -
t ion does n ot exist , t h e P CM will det er m in e t h e
pr oper in ject or pu lse widt h a n d con t in u e in ject ion .
Ba sed on t h e a bove in pu t s, t h e P CM will a dju st
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 t u r n in g t h e
gr ou n d pa t h t o t h e coil on a n d off.
WIDE OPEN THROTTLE MODE
Th is is a n Open Loop m ode. Du r in g wide open
t h r ot t le oper a t ion , t h e power t r a in con t r ol m odu le
(P CM) r eceives t h e followin g in pu t s.
• 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 )
Du r in g wide open t h r ot t le con dit ion 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 ign or es t h e oxygen sen sor in pu t
sign a l a n d pr ovides a pr edet er m in ed a m ou n t of a ddi-
t ion a l fu el. Th is is don e by a dju st in g in ject or pu lse
widt h .
• Th e P CM a dju st s ign it ion t im in g by t u r n in g t h e
gr ou n d pa t h t o t h e coil on a n d off.
IGNITION SWITCH OFF MODE
Wh en ign it ion swit ch is t u r n ed t o OF F posit ion ,
t h e P CM st ops oper a t in g t h e in ject or s, ign it ion coil,
ASD r ela y a n d fu el pu m p r ela y.
AIR CONDITIONING (A/C) CONTROLS—PCM
INPUT
OPERA TION
Th e A/C con t r ol syst em in for m a t ion a pplies t o fa c-
t or y in st a lled a ir con dit ion in g u n it s.
A/C S ELECT S IGN AL: Wh en t h e A/C swit ch is in
t h e ON posit ion , a n in pu t sign a l is sen t t o t h e P ow-
er t r a in Con t r ol Modu le (P CM). Th e sign a l in for m s
t h e P CM t h a t t h e A/C h a s been select ed. Th e P CM
a dju st s idle speed t o a pr e-pr ogr a m m ed r pm t h r ou gh
t h e idle a ir con t r ol (IAC) m ot or t o com pen sa t e for
in cr ea sed en gin e loa d.
A/C REQU ES T S IGN AL: On ce A/C h a s been
select ed, t h e P CM r eceives t h e A/C r equ est sign a l
fr om t h e clu t ch cyclin g pr essu r e swit ch . Th e in pu t
in dica t es t h a t t h e eva por a t or pr essu r e is in t h e
pr oper r a n ge for A/C a pplica t ion . Th e P CM u ses t h is
in pu t t o cycle t h e A/C com pr essor clu t ch (t h r ou gh t h e
A/C r ela y). It will a lso det er m in e t h e cor r ect en gin e
idle speed t h r ou gh t h e idle a ir con t r ol (IAC) m ot or
posit ion .
If t h e A/C low-pr essu r e swit ch or h igh -pr essu r e
swit ch open s (in dica t in g a low or h igh r efr iger a n t
pr essu r e), t h e P CM will n ot r eceive a n A/C r equ est
sign a l. Th e P CM will t h en r em ove t h e gr ou n d fr om
FUEL SYSTEM 14 - 27