Jeep Wrangler 1997 Manual page 799

TJ
DESCRIPTION AND OPERATION (Continued)
valve ports of the cylinder head . The engine wiring
harness connector for each fuel injector is equipped
with an attached numerical tag (INJ 1, INJ 2 etc .).
This is used to identify each fuel injector .
The injectors are energized individually in a
sequential order by the Powertrain Control Module
(PCM) . The PCM will adjust injector pulse width by
switching the ground path to each individual injector
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 PRESSURE
TEST PORT
(IF EQUIPPED)
FUEL RAIL
MOUNTING BOLTS
Fig. 11 Fuel Injectors-Typical 4.OL Shown
80524elf
IGNITION COIL-PCM OUTPUT
System voltage from the Automatic Shutdown
(ASD) relay is supplied to the ignition coil positive
terminal . The Powertrain Control Module (PCM)
operates the ignition coil. Ignition timing is not
adjustable . The PCM adjusts ignition timing to
meet changing engine operating conditions .
Refer to Group SD, Ignition System for additional
information.
MALFUNCTION INDICATOR LAMP-PCM OUTPUT
The malfunction indicator lamp illuminates each
time the ignition key is turned on. It will stay on for
approximately three seconds as a bulb test . The lamp
is displayed on the instrument panel as the CHECK
ENGINE lamp (Fig . 12) .
The signals needed to activate the lamp are sent
from the Powertrain Control Module (PCM) to the
instrument panel through the CCD bus circuits.
If the PCM receives an incorrect signal, or no sig-
nal from certain sensors or emission related systems,
FUEL SYSTEM 14- 27
Fig. 12 Check Engine Lamp Typical
the lamp is turned on. This is a warning that the
PCM has recorded a system or sensor malfunction . In
some cases, when a problem is declared, the PCM
will go into a limp-in mode. This is an attempt to
keep the system operating . It signals an immediate
need for service.
The lamp can also be used to display a Diagnostic
Trouble Code (DTC). Refer to On-Board Diagnostics
in Group 25, Emission Control System for additional
information.
The lamp is also used to display certain engine
misfires . Refer to Group 25, Emission Control System
for additional information .
TACHOMETER--PCM OUTPUT
The Powertrain Control Module (PCM) supplies
engine rpm values to the instrument cluster tachom-
eter through the PCM's CCD bus circuits. Refer to
Group 8E, Instrument Panel and Gauges for tachom-
eter information .
THROTTLE BODY
Filtered air from, the air cleaner enters the intake
manifold through the throttle body (Fig . 13) . Fuel
does not enter the intake manifold through the throt-
tle body. Fuel is sprayed into the manifold by the fuel
injectors . The throttle body is mounted on the intake
manifold . It contains an air control passage (Fig. 13)
controlled by an Idle Air Control (IAC) motor. The air
control passage is used to supply air for idle condi-
tions. A throttle valve (plate) is used to supply air for
above idle conditions .
The Throttle Position Sensor (TPS), IAC motor and
Manifold Absolute Pressure sensor (MAP) are
attached to the throttle body. The accelerator pedal
cable, speed control cable (when equipped) and auto-