Jeep Cherokee 1999 Electronic Service Manual page 1249

14 - 6 FUEL SYSTEM—2.5L DIESEL ENGINE
DESCRI PT I ON AN D OPERAT I ON (Cont inue d)
Fig. 6 Plastic Retainer Ring-Type Fitting
HIGH-PRESSURE FUEL LINES
CAUTION: The high–pressure fuel lines must be
held securely in place in their holders. The lines
cannot contact each other or other components. Do
not attempt to weld high–pressure fuel lines or to
repair lines that are damaged. Only use the recom-
mended lines when replacement of high–pressure
fuel line is necessary.
H igh –pr essu r e fu el lin es deliver fu el u n der pr es-
su r e of u p t o a ppr oxim a t ely 45,000 kP a (6526 psi)
fr om t h e in ject ion pu m p t o t h e fu el in ject or s. Th e
lin es expa n d a n d con t r a ct fr om t h e h igh –pr essu r e
fu el pu lses gen er a t ed du r in g t h e in ject ion pr ocess. All
h igh –pr essu r e fu el lin es a r e of t h e sa m e len gt h a n d
in side dia m et er. Cor r ect h igh –pr essu r e fu el lin e
u sa ge a n d in st a lla t ion is cr it ica l t o sm oot h en gin e
oper a t ion .
WARNING: USE EXTREME
INSPECTING FOR HIGH–PRESSURE FUEL LEAKS.
INSPECT FOR HIGH–PRESSURE FUEL LEAKS WITH
A SHEET OF CARDBOARD. HIGH FUEL INJECTION
PRESSURE CAN CAUSE PERSONAL INJURY IF
CONTACT IS MADE WITH THE SKIN.
FUEL DRAIN TUBES
Th ese r u bber t u bes a r e low–pr essu r e t ype.
Som e excess fu el is con t in u a lly ven t ed fr om t h e
fu el in ject ion pu m p. Du r in g in ject ion , a sm a ll a m ou n t
of fu el flows pa st t h e in ject or n ozzle a n d is n ot
CAUTION WHEN
in ject ed in t o t h e com bu st ion ch a m ber. Th is fu el
dr a in s in t o t h e fu el dr a in t u bes (F ig. 7) a n d ba ck t o
t h e t ee ba n jo fit t in g, wh ich is con n ect ed t o t h e sa m e
lin e a s t h e over flow va lve, wh ich a llows a va r ia ble
qu a n t it y t o r et u r n t o t h e fu el t a n k. Th e over flow
va lve is ca libr a t ed t o open a t a pr eset pr essu r e.
E xcess fu el n ot r equ ir ed by t h e pu m p t o m a in t a in t h e
m in im u m pu m p ca vit y pr essu r e is t h en r et u r n ed
t h r ou gh t h e over flow va lve a n d on t o t h e fu el t a n k
t h r ou gh t h e fu el r et u r n lin e.
Fig. 7 Fuel Drain Tubes
FUEL HEA TER
Th e fu el h ea t er is u sed t o pr even t diesel fu el fr om
wa xin g du r in g cold wea t h er oper a t ion . Th e fu el
h ea t er is loca t ed in t h e bot t om pla st ic bowl of t h e
fu el filt er /wa t er sepa r a t or (F ig. 8).
Th e elem en t in side t h e h ea t er a ssem bly is m a de of
a P osit ive Tem per a t u r e Coefficien t (P TC) m a t er ia l,
a n d h a s power a pplied t o it by t h e fu el h ea t er r ela y
a n yt im e t h e ign it ion key is in t h e "on " posit ion . P TC
m a t er ia l h a s a h igh r esist a n ce t o cu r r en t flow wh en
it s t em per a t u r e is h igh , wh ich m ea n s t h a t it will n ot
gen er a t e h ea t wh en t h e t em per a t u r e is a bove a cer-
t a in va lu e. Wh en t h e t em per a t u r e is below 7°C (45°
F ), t h e r esist a n ce of t h e P TC elem en t is lower ed, a n d
a llows cu r r en t t o flow t h r ou gh t h e fu el h ea t er ele-
m en t wa r m in g t h e fu el. Wh en t h e t em per a t u r e is
a bove 29°C (85° F ), t h e P TC elem en t 's r esist a n ce
r ises, a n d cu r r en t flow t h r ou gh t h e h ea t er elem en t
st ops.
Volt a ge t o oper a t e t h e fu el h ea t er is su pplied fr om
t h e ign it ion (key) swit ch a n d t h r ou gh t h e fu el h ea t er
r ela y. Refer t o t h e followin g F u el H ea t er Rela y for
X J