Jeep 1996 Grand Cherokee Service Manual - page 1082
on and off. Injector pulse width is the period of time
that the injector is energized. The PCM will adjust
injector pulse width based on various inputs it
receives.
During start up, battery voltage is supplied to the
injectors through the ASD relay. When the engine is
operating, voltage is supplied by the charging sys-
tem. The PCM determines injector pulse width based
on various inputs.
FUEL PUMP RELAY-PCM OUTPUT
The PCM energizes the electric fuel pump and the
oxygen sensor (O2S) heating element through the
fuel pump relay. Battery voltage is applied to the fuel
pump relay when the ignition key is ON. The relay is
energized when a ground signal is provided by the
PCM.
Refer to Automatic Shutdown Relay—PCM Output
for additional information.
The fuel pump will operate for approximately one
second unless the engine is operating or the starter
motor is engaged.
The fuel pump relay is located in the Power Distri-
bution Center (PDC) (Fig. 12).
GENERATOR FIELD—PCM OUTPUT
The powertrain control module (PCM) regulates
the charging system voltage within a range of 12.9 to
15.0 volts. Refer to Groups 8A and 8C for charging
system information.
GENERATOR LAMP—PCM OUTPUT
If the powertrain control module (PCM) senses a
low charging condition in the charging system, it will
illuminate the generator lamp (if equipped) on the
instrument panel. For example, during low idle with
all accessories turned on, the lamp may momentarily
go on. Once the PCM corrects idle speed to a higher
rpm, the lamp will go out. Refer to Groups 8A and
8C for charging system information.
IDLE AIR CONTROL (IAC) MOTOR—5.2L
ENGINES—PCM OUTPUT
The IAC motor is mounted to the back of the throt-
tle body (Fig. 10) and is controlled by the powertrain
control module (PCM).
The throttle body has an air control passage that
provides air for the engine at idle (the throttle plate
is closed). The IAC motor pintle protrudes into the
air control passage (Fig. 16) and regulates air flow
through it. Based on various sensor inputs, the pow-
ertrain control module (PCM) adjusts engine idle
speed by moving the IAC motor pintle in and out of
the air control passage. The IAC motor is positioned
when the ignition key is turned to the On position.
A (factory adjusted) set screw is used to mechani-
cally limit the position of the throttle body throttle
plate. Never attempt to adjust the engine idle
speed using this screw. All idle speed functions are
controlled by the PCM.
IDLE AIR CONTROL (IAC) MOTOR—4.0L
ENGINE—PCM OUTPUT
The IAC motor is mounted on the throttle body
(Fig. 9) and is controlled by the powertrain control
module (PCM).
The throttle body has an air control passage that
provides air for the engine at idle (the throttle plate
is closed). The IAC motor pintle protrudes into the
air control passage and regulates air flow through it.
Based on various sensor inputs, the powertrain con-
trol module (PCM) adjusts engine idle speed by mov-
ing the IAC motor pintle in and out of the air control
passage. The IAC motor is positioned when the igni-
tion key is turned to the On position.
Fig. 15 Fuel Injectors—4.0L Engine
Fig. 16 Throttle Body Air Control Passage—5.2L
Engine
ZJ
FUEL SYSTEM
14 - 37
DESCRIPTION AND OPERATION (Continued)