Jeep Cherokee 1999 Electronic Service Manual page 1226

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DESCRI PT I ON AN D OPERAT I ON (Cont inue d)
FUEL PUMP RELA Y-PCM OUTPUT
DESCRIPTION
Th e fu el pu m p r ela y is loca t ed in t h e P ower Dist r i-
bu t ion Cen t er (P DC).
OPERA TION
Th e P CM en er gizes t h e elect r ic fu el pu m p t h r ou gh
t h e fu el pu m p r ela y. Ba t t er y volt a ge is a pplied t o t h e
fu el pu m p r ela y wh en t h e ign it ion key is ON. Th e
r ela y is en er gized wh en a gr ou n d sign a l is pr ovided
by t h e P CM.
Th e fu el pu m p will oper a t e for a ppr oxim a t ely t h r ee
secon ds u n less t h e en gin e is oper a t in g or t h e st a r t er
m ot or is en ga ged.
GENERA TOR FIELD SOURCE (+)—PCM
OUTPUT
OPERA TION
Th is ou t pu t fr om t h e P ower t r a in Con t r ol Modu le
(P CM) r egu la t es ch a r gin g syst em volt a ge t o t h e gen -
er a t or field sou r ce (+) cir cu it . Th e volt a ge r a n ge is
12.9 t o 15.0 volt s. Models of pr eviou s yea r s h a d u sed
t h e ASD r ela y (dir ect ly) t o a pply t h e 12 volt + power
su pply t o t h e gen er a t or field sou r ce (+) cir cu it .
GENERA TOR FIELD DRIVER (-)—PCM OUTPUT
OPRA TION
Th is ou t pu t fr om t h e P ower t r a in Con t r ol Modu le
(P CM) r egu la t es ch a r gin g syst em gr ou n d con t r ol t o
t h e gen er a t or field dr iver (-) cir cu it .
GENERA TOR LAMP—PCM OUTPUT
If t h e power t r a in con t r ol m odu le (P CM) sen ses a
low ch a r gin g con dit ion in t h e ch a r gin g syst em , it will
illu m in a t e t h e gen er a t or la m p (if equ ipped) on t h e
in st r u m en t pa n el. F or exa m ple, du r in g low idle wit h
a ll a ccessor ies t u r n ed on , t h e la m p m a y m om en t a r ily
go on . Refer t o Gr ou ps 8A a n d 8C for ch a r gin g sys-
t em in for m a t ion .
IDLE AIR CONTROL (IAC) MOTOR—PCM
OUTPUT
Th e IAC m ot or is m ou n t ed on t h e t h r ot t le body
(F ig. 7) a n d is con t r olled by t h e P ower t r a in Con t r ol
Modu le (P CM).
Th e t h r ot t le body h a s a n a ir con t r ol pa ssa ge t h a t
pr ovides a ir for t h e en gin e a t idle (t h e t h r ot t le pla t e
is closed). Th e IAC m ot or pin t le pr ot r u des in t o t h e
a ir con t r ol pa ssa ge a n d r egu la t es a ir flow t h r ou gh it .
Ba sed on va r iou s sen sor in pu t s, t h e P CM a dju st s
en gin e idle speed by m ovin g t h e IAC m ot or pin t le in
a n d ou t of t h e a ir con t r ol pa ssa ge. Th e IAC m ot or is
posit ion ed wh en t h e ign it ion key is t u r n ed t o t h e On
posit ion .
A (fa ct or y a dju st ed) set scr ew is u sed t o m ech a n i-
ca lly lim it t h e posit ion of t h e t h r ot t le body t h r ot t le
pla t e. N e v e r a tte m p t to a d ju s t th e e n g in e id le
s p e e d u s in g th is s c re w. All idle speed fu n ct ion s a r e
con t r olled by t h e P CM.
IGNITION COIL—PCM OUTPUT
Syst em volt a ge fr om t h e Au t om a t ic Sh u t down
(ASD) r ela y is su pplied t o t h e ign it ion coil posit ive
t er m in a l. Th e P ower t r a in Con t r ol Modu le (P CM)
oper a t es t h e ign it ion coil. Ig n itio n tim in g is n o t
a d ju s ta ble . Th e P CM a dju st s ign it ion t im in g t o
m eet ch a n gin g en gin e oper a t in g con dit ion s.
Refer t o Gr ou p 8D, Ign it ion Syst em for a ddit ion a l
in for m a t ion .
LEAK DETECTION PUMP—PCM OUTPUT
Cer t a in en gin es wit h cer t a in em ission s pa cka ges
a r e equ ipped wit h a lea k det ect ion pu m p (LDP ). Th e
LDP is a ct iva t ed t h r ou gh t h is P CM ou t pu t . Refer t o
Gr ou p 25, E m ission Con t r ol Syst em for a ddit ion a l
in for m a t ion .
RADIA TOR FAN RELA Y—PCM OUTPUT
An elect r ic r a dia t or coolin g fa n is u sed wit h cer t a in
m odels/en gin es. It is con t r olled by t h e power t r a in
con t r ol m odu le (P CM) t h r ou gh t h e r a dia t or fa n r ela y.
Th e r ela y is en er gized wh en coola n t t em per a t u r e is
a bove 103°C (217°F ). It will t h en de-en er gize wh en
coola n t t em per a t u r e dr ops t o 98°C (208°F ). Refer t o
Gr ou p 7, Coolin g Syst em s for m or e in for m a t ion .
Th e r ela y is loca t ed in t h e power dist r ibu t ion cen -
t er (P DC) (F ig. 12).
MALFUNCTION INDICA TOR LAMP—ECM/PCM
OUTPUT
Refer t o Gr ou p 25, E m ission Con t r ol Syst em for
in for m a t ion .
SPEED CONTROL SOLENOIDS—PCM OUTPUT
Speed con t r ol oper a t ion is r egu la t ed by t h e power-
t r a in con t r ol m odu le (P CM). Th e P CM con t r ols t h e
va cu u m t o t h e t h r ot t le a ct u a t or t h r ou gh t h e speed
con t r ol va cu u m a n d ven t solen oids. Refer t o Gr ou p
8H for Speed Con t r ol In for m a t ion .
TACHOMETER—PCM OUTPUT
Th e power t r a in con t r ol m odu le (P CM) su pplies
en gin e r pm va lu es t o t h e in st r u m en t clu st er t a ch om -
et er. Refer t o Gr ou p 8E for t a ch om et er in for m a t ion .
THROTTLE BODY
F ilt er ed a ir fr om t h e a ir clea n er en t er s t h e in t a ke
m a n ifold t h r ou gh t h e t h r ot t le body (F ig. 16). F u el
FUEL SYSTEM 14 - 35