1995 ISUZU TROOPER Workshop Manual

Throttle Position (TP) Sensor
The Throttle Position (TP) Sensor is mounted on the
side
of the throttle body opposite the throttle lever
assembly.
Its function is to sense the current throttle
body position and relay that information to the ECM.
Knowledge ofTP is needed by the ECM to generate the
proper injector pulse width.
If the TP sensor senses a
Wide
Open Throttle, a voltage signal indicating this
condition is transmitted to the
ECM. The ECM will
widen the injector pulse, or increase the repetition rate,
permitting increased fuel
flow to each for the six fuel
injectors located in the fuel fail. As the throttle shaft
rotates in response to
movement of the accelerator
pedal (opening
or closing of the throttle body), the
throttle shaft transmits throttle
movement to the TP
sensor. A potentiometer (variable resistor) within the
TP sensor assembly creates a voltage that varies in
response to
TP. By applying a reference voltage (+5
VDC) to the TP sensor input, a varying voltage
(reflecting
TP) is available at the TP sensor output. The
voltage
output from the TP sensor is sent to the ECM
for use in determining current TP.
For further information ofTP sensor, refer to "ECM and
Sensors", Section
"6E2-C1 ". The TP sensor is an auto
zeroing type and cannot
be adjusted.
DRIVEABILITY AND EMISSIONS 6E2-121
INDUCTION AIR CONTROL PLATE
SYSTEM (DOHC) (Fig. 6E2-74)
This system consists of the Induction Air control plate
valve mounted in the common chamber
duct and a
vacuum operated diaphragm
which moves the Induction Air
Control Plate linkage. The vacuum to the diaphragm is
turned
"ON" or "OFF" by a vacuum switching solenoid
which is electrically operated by the
ECM.
Refer to CHART C-20 for diagnosing the Induction air
control plate system.
Manifold vaccum
1
Vacuum actuator
Induction air control plate valve
(noma! open)
Fig. 6E2-74
Engine control module (ECM)
Ignition switch
Canister, EGR, A.I.R. solenoids
DIAGNOSIS
FUEL METERING SYSTEM
Some failures of this system will result in the symptom,
"Engine Cranks But Will Not Run". If this condition
exists, see CHART A-3. This chart will determine
if the
problem is caused by the ignition system,
ECM or fuel
pump circuit.
If it's determined to be a fuel problem.
CHART A-5
or A-7 will be used. This includes the
injectors, fuel pressure control valve, fuel
pump and
fuel pump relay. The fuel system
wiring schematic
diagram is covered on the facing page
of CHART A-5.
If a malfunction occurs in the fuel control system, it
usually results in either a rich or lean Heated Oxygen
Sensor (H02S) signal condition. This condition is
sensed by the
H02S and the ECM will change the fuel
calculation (injector pulse width) based on
H02S input.
The change made to the fuel calculation will be
indicated
by a change in the block learn values which
can be displayed on a
"Scan tool". The ideal block learn
values are around 128 counts.
If the H02S senses a
lean condition, the
ECM will add fuel, resulting in a
block learn value above 128 counts.
If the H02S senses
a rich condition, the
ECM will subtract fuel, resulting in
a block learn value below 128 counts.
Block learn values can vary greatly, depending on
temperature, altitude and individual engine
tolerances. The programmed range for block learn
values is
58 to 198. Values within this range indicate
the system is in
"control". If a system is operating near
the extremes
of the block learn range during normal vehicle
operation, and there is a driveability complaint,
the fuel metering system should be checked. Refer to
the diagnostic trouble code
45 chart on the facing page
for potential causes of a rich condition (low block learn
values). Refer to the diagnostic trouble code 44 chart
facing page
for potential causes of a lean condition
(high block learn values).
If a driveability symptom
exists, also refer to the particular symptom in
"Symptoms", Section "6E2-B" for additional items to
check.
FUEL SYSTEM PRESSURE TEST
A fuel system pressure test procedure is included in
CHART A-7 under
"Fuel System Diagnosis" in "Engine
Components/Wiring Diagrams/Diagnostic
Charts",
Section "6E2-A" diagnostic charts.
IDLE AIR CONTROL (lAC) VALVE
A "Scan tool" will display Idle Air Control (lAC) valve
position in
"Counts" or steps. "0" steps indicates the
ECM is commanding the lAC valve to be driven all the
way in, to a fully seated position. This condition is
usually caused by a vacuum leak.
The higher the number
of counts, the more air is being
allowed to pass the
lAC valve. A functional check of the
lAC valve system (CHART C-2C) is provided in this
section. Refer to
"Refer, Unstable, or Incorrect Idle,
Stalling"
in "Symptoms", Section "6E2-B" for other
possibilities
for the cause of idle problems.

6E2-122 DRIVEABILITV AND EMISSIONS
INDUCTION AIR CONTROL PLATE
SYSTEM
Refer to CHART C-2D to diagnose the Induction air
control plate system.
ON-VEHICLE SERVICE
FUEL PUMP RELAY
The fuel pump relay is mounted in the engine
compartment.
Other than checking for loose
connectors, the only service possible is replacement.
MUL TIPORT FUEL INJECTION
COMPONENTS
WCAUTION:
VI • To reduce the risk of fire and personal injury, it
is necessary to relieve the fuel system pressure
before servicing
fuel system components.
• After relieving system pressure, a small
amount of fuel may be released when servicing
fuel lines or connections. In order to reduce the
chance
of personal injury, cover fuel line
fittings with a shop towel before disconnecting,
to catch any
fuel that may leak out. Place the
towel in an approved container when
disconnect is completed.
Fuel Pressure Relief Procedure
1. Remove fuel cap.
2. Remove fuel pump relay from underhood relay
box.
3. Start engine and allow to stall.
4. Crank engine for additional 30 seconds.
5. Remove negative battery cable.
FUEL RAIL ASSEMBL V
An eight digit identification number is stamped on the
side
ofthe fuel rail (Fig. 6E2-75). Refer to this number if
servicing or part replacement is required.
Names
of component parts appear in the numbered
list on the disassembled view (Fig. 6E2-75).
'fCAUTION:
• Do not attempt to remove the fuel inlet fitting
on the
fuel rail, it is staked in place. To do so will
result
in damage to the fuel rail or to the internal
0-ring seal.
•
Do care in removing the fuel rail assembly, to
prevent damage to the injector
electrical
connector terminals and the injector spray tips.
• Prevent dirt and other contaminants from
entering open lines and passages. Fittings
should be capped, and holes plugged, during
servicing.
Before
removal, the fuel rail assembly may be
cleaned with a spray type engine cleaner,
following
package instructions. Do not
immerse fuel rails in liquid cleaning solvent.
Fig. 6E2-75
I'
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•

DRIVEABILITY AND EMISSIONS 6E2-123
UNIT REPAIR
FUEL INJECTOR/RAIL
1 11
5
9
13
5 14
2 12 5
15
3
6
Fig. 6E2-76