Jeep Cherokee 1999 Electronic Service Manual page 1025

9 - 8 ENGINE
DIAGNOSIS AND TESTING
CYLINDER COMBUSTION PRESSURE
LEAKAGE TEST . . . . . . . . . . . . . . . . . . . . . . . . 9
CYLINDER COMPRESSION PRESSURE TEST . . 8
ENGINE CYLINDER HEAD GASKET FAILURE
DIAGNOSIS . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
DI AGN OSI S AN D T EST I N G
GENERAL INFORMA TION
E n gin e dia gn osis is h elpfu l in det er m in in g t h e
ca u ses of m a lfu n ct ion s n ot det ect ed a n d r em edied by
r ou t in e m a in t en a n ce.
Th ese m a lfu n ct ion s m a y be cla ssified a s eit h er per-
for m a n ce (e.g., en gin e idles r ou gh a n d st a lls) or
m ech a n ica l (e.g., a st r a n ge n oise).
Refer t o t h e Ser vice Dia gn osis—P er for m a n ce ch a r t
a n d t h e Ser vice Dia gn osis—Mech a n ica l ch a r t for pos-
sible ca u ses a n d cor r ect ion s of m a lfu n ct ion s. Refer t o
Gr ou p 14, F u el Syst em for t h e fu el syst em dia gn osis.
Addit ion a l t est s a n d dia gn ost ic pr ocedu r es m a y be
n ecessa r y for specific en gin e m a lfu n ct ion s t h a t ca n
n ot be isola t ed wit h t h e Ser vice Dia gn osis ch a r t s.
In for m a t ion con cer n in g a ddit ion a l t est s a n d dia gn o-
sis is pr ovided wit h in t h e followin g dia gn osis:
• Cylin der Com pr ession P r essu r e Test .
• Cylin der Com bu st ion P r essu r e Lea ka ge Test .
• E n gin e Cylin der H ea d Ga sket F a ilu r e Dia gn osis.
• In t a ke Ma n ifold Lea ka ge Dia gn osis.
INTAKE MANIFOLD LEAKAGE DIAGNOSIS
An in t a ke m a n ifold a ir lea k is ch a r a ct er ized by
lower t h a n n or m a l m a n ifold va cu u m . Also, on e or
m or e cylin der s m a y n ot be fu n ct ion in g.
WARNING: USE EXTREME CAUTION WHEN THE
ENGINE IS OPERATING. DO NOT STAND IN A
DIRECT LINE WITH THE FAN. DO NOT PUT YOUR
HANDS NEAR THE PULLEYS, BELTS OR THE FAN.
DO NOT WEAR LOOSE CLOTHING.
(1) St a r t t h e en gin e.
(2) Spr a y a sm a ll st r ea m of wa t er a t t h e su spect ed
lea k a r ea .
(3) If a ch a n ge in RP M is obser ved t h e a r ea of t h e
su spect ed lea k h a s been fou n d.
(4) Repa ir a s r equ ir ed.
EN GI N E DI AGN OSI S
INDEX
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CYLINDER COMPRESSION PRESSURE TEST
ca n be u t ilized t o dia gn ose sever a l en gin e m a lfu n c-
t ion s.
en gin e st a r t er m ot or is in good oper a t in g con dit ion .
Ot h er wise t h e in dica t ed com pr ession pr essu r es m a y
n ot be va lid for dia gn osis pu r poses.
a ir.
F u el Syst em for t h e cor r ect pr ocedu r e)
t h e en gin e wit h t h e en gin e st a r t er m ot or for t h r ee
r evolu t ion s.
r evolu t ion . Con t in u e t h e t est for t h e r em a in in g cylin -
der s.
en gin e com pr ession pr essu r es.
ENGINE CYLINDER HEAD GASKET FAILURE
DIAGNOSIS
r esu lt s in loss of power, loss of coola n t a n d en gin e
m isfir in g.
bet ween a dja cen t cylin der s or bet ween a cylin der a n d
t h e a dja cen t wa t er ja cket .
a dja cen t cylin der s is in dica t ed by a loss of power
a n d/or en gin e m isfir e.
a cylin der a n d a n a dja cen t wa t er ja cket is in dica t ed
by coola n t foa m in g or over h ea t in g a n d loss of coola n t .
ENGINE OIL LEAK INSPECTION . . . . . . . . . . . . 10
ENGINE OIL PRESSURE . . . . . . . . . . . . . . . . . . 10
GENERAL INFORMATION . . . . . . . . . . . . . . . . . . 8
INTAKE MANIFOLD LEAKAGE DIAGNOSIS . . . . . 8
SERVICE DIAGNOSIS—MECHANICAL . . . . . . . . 13
SERVICE DIAGNOSIS—PERFORMANCE . . . . . . 11
Th e r esu lt s of a cylin der com pr ession pr essu r e t est
E n su r e t h e ba t t er y is com plet ely ch a r ged a n d t h e
(1) Clea n t h e spa r k plu g r ecesses wit h com pr essed
(2) Rem ove t h e spa r k plu gs.
(3) Secu r e t h e t h r ot t le in t h e wide-open posit ion .
(4) Disa ble t h e fu el syst em . (Refer t o Gr ou p 14,
(5) Discon n ect t h e ign it ion coil.
(6) In ser t a com pr ession pr essu r e ga u ge a n d r ot a t e
(7) Recor d t h e com pr ession pr essu r e on t h e 3r d
Refer t o E n gin e Specifica t ion s for t h e cor r ect
A lea kin g en gin e cylin der h ea d ga sket u su a lly
An en gin e cylin der h ea d ga sket lea k ca n be loca t ed
• An en gin e cylin der h ea d ga sket lea kin g bet ween
• An en gin e cylin der h ea d ga sket lea kin g bet ween
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