Jeep Cherokee 1999, Electronic Service Manual

Page: 316 / 1948

t h e sen sor in pu t t o det er m in e t h e cr a n ksh a ft posi-
t ion . Th e P CM t h en u ses t h is posit ion , a lon g wit h
ot h er in pu t s, t o det er m in e in ject or sequ en ce a n d ign i-
t ion t im in g.
Th e sen sor is a h a ll effect device com bin ed wit h a n
in t er n a l m a gn et . It is a lso sen sit ive t o st eel wit h in a
cer t a in dist a n ce fr om it .
SENSOR OPERATION
Th e flywh eel/dr ive pla t e h a s gr ou ps of fou r n ot ch es
a t it s ou t er edge. On 4.0L 6-cylin der en gin es t h er e
a r e t h r ee set s of n ot ch es (F ig. 5). On 2.5L 4-cylin der
en gin es t h er e a r e t wo set s of n ot ch es (F ig. 4).
Th e n ot ch es ca u se a pu lse t o be gen er a t ed wh en
t h ey pa ss u n der t h e sen sor. Th e pu lses a r e t h e in pu t
t o t h e P CM. F or ea ch en gin e r evolu t ion t h er e a r e t wo
gr ou ps of fou r pu lses gen er a t ed on 2.5L 4-cylin der
en gin es. Th er e a r e 3 gr ou ps of fou r pu lses gen er a t ed
on 4.0L 6-cylin der en gin es.
Th e t r a ilin g edge of t h e fou r t h n ot ch , wh ich ca u ses
t h e pu lse, is fou r degr ees befor e t op dea d cen t er
(TDC) of t h e cor r espon din g pist on .
Th e en gin e will n ot oper a t e if t h e P CM does n ot
r eceive a cr a n ksh a ft posit ion sen sor in pu t .
CAMSHAFT POSITION SENSOR
Th e ca m sh a ft posit ion sen sor is loca t ed in t h e dis-
t r ibu t or on a ll en gin es.
Th e sen sor con t a in s a h a ll effect device ca lled a
syn c sign a l gen er a t or t o gen er a t e a fu el syn c sign a l.
Th is syn c sign a l gen er a t or det ect s a r ot a t in g pu lse
r in g (sh u t t er ) on t h e dist r ibu t or sh a ft . Th e pu lse r in g
r ot a t es 180 degr ees t h r ou gh t h e syn c sign a l gen er a -
t or. It s sign a l is u sed in con ju n ct ion wit h t h e cr a n k-
sh a ft posit ion sen sor t o differ en t ia t e bet ween fu el
in ject ion a n d spa r k even t s. It is a lso u sed t o syn ch r o-
n ize t h e fu el in ject or s wit h t h eir r espect ive cylin der s.
Wh en t h e lea din g edge of t h e pu lse r in g (sh u t t er )
en t er s t h e syn c sign a l gen er a t or, t h e followin g occu r s:
Th e in t er r u pt ion of m a gn et ic field ca u ses t h e volt a ge
t o swit ch h igh r esu lt in g in a syn c sign a l of a ppr oxi-
m a t ely 5 volt s.
Fig. 3 Crankshaft Position Sensor—Typical
Fig. 4 Sensor Operation—2.5L 4-Cyl. Engine
Fig. 5 Sensor Operation—4.0L 6-Cyl. Engine
X J IGNITION SYSTEM 8D - 3
DESCRI PT I ON AN D OPERAT I ON (Cont inue d)