Jeep Cherokee 1999 Electronic Service Manual page 1253

14 - 10 FUEL SYSTEM—2.5L DIESEL ENGINE
DI AGN OSI S AN D T EST I N G (Cont inue d)
Fig. 18 Vaccum Pump at Front of Engine
(24) Ver ify t h er e is a good con n ect ion a t t h e Boost
P r essu r e Sen sor, wh ich is a pa r t of t h e a ir in t a ke
a ssem bly.
AIR IN FUEL SYSTEM
Air will en t er t h e fu el syst em wh en ever t h e fu el
su pply lin es, fu el filt er /wa t er sepa r a t or, fu el filt er
bowl, in ject ion pu m p, h igh –pr essu r e lin es or in ject or s
a r e r em oved or discon n ect ed. Air will a lso en t er t h e
fu el syst em wh en ever t h e fu el t a n k h a s been r u n
em pt y.
Air t r a pped in t h e fu el syst em ca n r esu lt in h a r d
st a r t in g, a r ou gh r u n n in g en gin e, en gin e m isfir e, low
power, excessive sm oke a n d fu el kn ock. Aft er ser vice
is per for m ed, a ir m u st be bled fr om t h e syst em
befor e st a r t in g t h e en gin e.
In spect t h e fu el syst em fr om t h e fu el t a n k t o t h e
in ject or s for loose con n ect ion s. Lea kin g fu el is a n
in dica t or of loose con n ect ion s or defect ive sea ls. Air
ca n a lso en t er t h e fu el syst em bet ween t h e fu el t a n k
a n d t h e in ject ion pu m p. In spect t h e fu el t a n k a n d
fu el lin es for da m a ge t h a t m igh t a llow a ir in t o t h e
syst em .
F or a ir bleedin g, r efer t o Air Bleed P r ocedu r e in
t h e Ser vice P r ocedu r es sect ion of t h is gr ou p.
FUEL HEA TER RELA Y TEST
Th e fu el h ea t er r ela y is loca t ed in t h e P ower Dis-
t r ibu t ion Cen t er (P DC). Refer t o Rela ys—Oper a t ion /
Test in g in F u el In ject ion Syst em sect ion of t h is gr ou p
for t est pr ocedu r es.
FUEL INJECTOR TEST
Th e fu el in ject ion n ozzles, loca t ed on t h e en gin e
cylin der h ea d, spr a y fu el u n der h igh pr essu r e in t o
t h e in dividu a l com bu st ion ch a m ber s. P r essu r ized
fu el, deliver ed by t h e fu el in ject ion pu m p, u n sea t s a
spr in g-loa ded n eedle va lve in side t h e in ject or, a n d
t h e fu el is a t om ized a s it esca pes t h r ou gh t h e in ject or
open in g in t o t h e en gin e's com bu st ion ch a m ber. If t h e
fu el in ject or does n ot oper a t e pr oper ly, t h e en gin e
m a y m isfir e, or ca u se ot h er dr ivea bilit y pr oblem s.
A lea k in t h e in ject ion pu m p–t o–in ject or h igh –pr es-
su r e fu el lin e ca n ca u se m a n y of t h e sa m e sym pt om s
a s a m a lfu n ct ion in g in ject or. In spect for a lea k in t h e
h igh –pr essu r e lin es befor e ch eckin g for a m a lfu n c-
t ion in g fu el in ject or.
WARNING: THE INJECTION
HIGH–PRESSURE FUEL OF UP TO APPROXI-
MATELY 45,000 KPA (6526 PSI) TO EACH INDIVID-
UAL INJECTOR THROUGH THE HIGH–PRESSURE
LINES. FUEL UNDER THIS AMOUNT OF PRESSURE
CAN PENETRATE THE SKIN AND CAUSE PER-
SONAL INJURY. WEAR SAFETY GOGGLES AND
ADEQUATE PROTECTIVE CLOTHING. AVOID CON-
TACT WITH FUEL SPRAY WHEN BLEEDING HIGH–
PRESSURE FUEL LINES.
WARNING: DO NOT BLEED AIR FROM THE FUEL
SYSTEM OF A HOT ENGINE. DO NOT ALLOW FUEL
TO SPRAY ONTO THE EXHAUST MANIFOLD WHEN
BLEEDING AIR FROM THE FUEL SYSTEM.
To det er m in e wh ich fu el in ject or is m a lfu n ct ion in g,
r u n t h e en gin e a n d loosen t h e h igh –pr essu r e fu el lin e
n u t a t t h e in ject or (F ig. 19). List en for a ch a n ge in
en gin e speed. If en gin e speed dr ops, t h e in ject or wa s
oper a t in g n or m a lly. If en gin e speed r em a in s t h e
sa m e, t h e in ject or m a y be m a lfu n ct ion in g. Aft er t est -
in g, t igh t en t h e lin e n u t t o 30 N·m (22 ft . lbs.)
t or qu e. Test a ll in ject or s in t h e sa m e m a n n er on e a t
a t im e.
On ce a n in ject or h a s been fou n d t o be m a lfu n ct ion -
in g, r em ove it fr om t h e en gin e a n d t est it . Refer t o
t h e Rem ova l/In st a lla t ion sect ion of t h is gr ou p for pr o-
cedu r es.
Aft er t h e in ject or h a s been r em oved, in st a ll it t o a
ben ch –m ou n t in ject or
in st r u ct ion s su pplied wit h t est er for pr ocedu r es.
Th e open in g pr essu r e or "pop" pr essu r e sh ou ld be
15,000–15,800 kP a (2175–2291 psi). If t h e fu el in jec-
t or n eedle va lve is open in g ("poppin g") t o ea r ly or t o
la t e, r epla ce t h e in ject or.
PUMP SUPPLIES
t est er. Refer t o oper a t in g
X J