Jeep Cherokee 1999 Electronic Service Manual page 1269

14 - 26 FUEL SYSTEM—2.5L DIESEL ENGINE
DESCRI PT I ON AN D OPERAT I ON (Cont inue d)
t u r n ed t o t h e ON posit ion . Th is sign a l in it ia t es t h e
glow plu g con t r ol r ou t in e t o begin t h e "pr e–h ea t "
cycle.
IGNITION CIRCUIT SENSE—PCM INPUT
Th e ign it ion cir cu it sen se in pu t sign a ls t h e P CM
t h a t t h e ign it ion (key) swit ch h a s been t u r n ed t o t h e
ON posit ion . Th is sign a l in it ia t es t h e glow plu g con -
t r ol r ou t in e t o begin t h e "pr e–h ea t " cycle.
POWER GROUND
P r ovides a com m on gr ou n d for power devices (sole-
n oid a n d r ela y devices).
NEEDLE MOVEMENT OR INSTRUMENTED
FIRST INJECTOR—ECM INPUT
Th is in pu t fr om t h e E CM su pplies a con st a n t 30
m A elect r ica l cu r r en t sou r ce for t h e fir st in ject or sen -
sor. It will va r y t h e volt a ge t o t h is sen sor wh en it
sen ses a m ech a n ica l m ovem en t wit h in t h e in ject or
n eedle (pin t le) of t h e n u m ber –1 cylin der fu el in ject or.
Wh en t h is volt a ge h a s been det er m in ed by t h e E CM,
it will t h en con t r ol a n ou t pu t t o t h e fu el t im in g sole-
n oid (t h e fu el t im in g solen oid is loca t ed on t h e fu el
in ject ion pu m p). Also r efer t o F u el In ject ion P u m p for
a ddit ion a l in for m a t ion .
Th e fir st in ject or sen sor is a m a gn et ic (in du ct ive)
t ype.
Th e fir st in ject or sen sor is u sed on ly on t h e fu el
in ject or for t h e n u m ber –1 cylin der (F ig. 4). It is n ot
u sed on t h e in ject or s for cylin der s n u m ber 2, 3, or 4.
FUEL INJECTOR SENSOR—GROUND
Fig. 4 Fuel Injector Sensor
P r ovides a low n oise gr ou n d for t h e fu el in ject or
sen sor on ly.
ENGINE COOLANT TEMPERA TURE SENSOR—
ECM/PCM INPUT
Th e 0–5 volt in pu t fr om t h is sen sor t ells t h e E CM
a n d P CM t h e t em per a t u r e of t h e en gin e coola n t .
Ba sed on t h e volt a ge r eceived a t t h e E CM, it will
t h en det er m in e oper a t ion of t h e fu el t im in g solen oid,
glow plu g r ela y, elect r ica l va cu u m m odu la t or (em is-
sion com pon en t ) a n d gen er a t or (ch a r gin g syst em ).
Th e sen sor is loca t ed on t h e side of t h e #3 cylin der
h ea d n ea r t h e r ea r of fu el in ject ion pu m p (F ig. 5).
Fig. 5 Engine Coolant Temperature Sensor Location
ENGINE SPEED/CRANK POSITION SENSOR—
ECM INPUT
Th e en gin e speed sen sor is m ou n t ed t o t h e t r a n s-
m ission bellh ou sin g a t t h e left /r ea r side of t h e en gin e
block (F ig. 6).
Fig. 6 Engine Speed Sensor Location
X J