1995 ISUZU TROOPER Workshop Manual

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Page 809 of 1928

ISUZU TROOPER 1995 Workshop Manual DRIVEABILITY AND EMISSIONS 6E2-113
CHART C-1E
POWER STEERING PRESSUR,.E (PSP) SWITCH DIAGNOSIS
CD • WITH ENGINE IDLING, "SCAN TOOL" SHOULD DISPLAY POWER STEERING PRESSURE (PSP) SWITCH TO BE "

Page 810 of 1928

ISUZU TROOPER 1995 Workshop Manual 6E2-114 DRIVEABILITY AND EMISSIONS
CHART C-1F
HEATED OXYGEN SENSOR (H02S} HEATER CHECK
Circuit Description:
The generator charging circuit supplies battery voltage to the heater part of Heated

Page 811 of 1928

ISUZU TROOPER 1995 Workshop Manual DRIVEABILITY AND EMISSIONS 6E2-115
CHART C-1F
HEATED OXYGEN SENSOR (H02S) HEATER CHECK
CD • IGNITION "OFF"
• DISCONNECT FOUR PIN CONNECTOR TO HEATED OXYGEN SENSOR (H02S).
• IGNITION "ON

Page 812 of 1928

ISUZU TROOPER 1995 Workshop Manual 6E2-116 DRIVEABILITY AND EMISSIONS
SECTION C-2
FUEL METERING SYSTEM
CONTENTS
General Description ...................... 6E2-116
Purpose ............................ 6E2-116
Modes of Operation .

6E2-116 DRIVEABILITY AND EMISSIONS
SECTION C-2
FUEL METERING SYSTEM
CONTENTS
General Description ...................... 6E2-116
Purpose ............................ 6E2-116
Modes of Operation .................... 6E2-117
Starting Mode ...................... 6E2-117
Clear Flood Mode .................... 6E2-117
RunMode ......................... 6E2-117
"Open Loop" ....................... 6E2-117
"Closed Loop" ...................... 6E2-117
Acceleration Mode ................... 6E2-117
Deceleration Mode ................... 6E2-117
Battery Positive Voltage Correction Mode ... 6E2-117
Fuel Cutoff Mode .................... 6E2-117
Fuel Metering System Components ........... 6E2-118
Fuel Supply System .................... 6E2-118
Fuel Pump Electrical Circuit ............... 6E2-118
Fuel Rail Assembly ..................... 6E2-118
Fuel Injectors ......................... 6E2-119
Fuel Injector Driver Operation ............. 6E2-119
Fuel Pressure Control Valve Assembly ....... 6E2-119
Throttle Body (TB) Assembly .............. 6E2-120
Idle Air Control (lAC) Valve .............. 6E2-120
Throttle Position (TP) Sensor ............ 6E2-121
Induction Air Control Plate System ......... 6E2-121
Diagnosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6E2-121
Fuel Metering System . .

. . . . . . . . . . . . . . . . 6E2-121
Fuel System Pressure Test ............... 6E2-121
Idle Air Control (lAC) Valve . .

. . . . . . . . . . . . . 6E2-121
Induction Air Control Plate System ......... 6E2-122
On-Vehicle Service ...................... 6E2-122
Fuel Pump Relay . . . . . . . . . . . . . . . . . . . . . . 6E2-122
Multipart Fuel Injection Components . . . . . . . . 6E2-122 Fuel Pressure Relief Procedure . . . . . . . . . . 6E2-122
Fuel Rail Assembly . . . . . . . . . . . . . . . . . . . . 6E2-122
Unit Repair ............................ 6E2-123
Fuel Injector/Rail ...................... 6E2-123
Throttle Body Assembly . . . . . . . . . . . . . . . . . 6E2-124
Throttle Body (TB) . . . . . . . . . . . . . . . . . . . 6E2-125
Throttle Position (TP) Sensor . . . . . . . . . . . . . 6E2-126
Idle Air Control (lAC) Valve ............... 6E2-126
Minimum Throttle Body (TB) Position Check ... 6E2-127
Chart C-2A Injector Balance ................ 6E2-128
Chart C-2C Idle Air Control (lAC) System Check .. 6E2-130
Chart C-2D Induction Air Control Plate
System Check . .
. . . . . . . . . . . . . . . . . . . . . . 6E2-132
GENERAL DESCRIPTION
PURPOSE
The function of the fuel metering system is to deliver
the correct amount of fuel to the engine under all
operating conditions. Fuel is delivered to the engine by
individual fuel injectors mounted in the intake manifold
near each cylinder.
The main control sensor is the heated oxygen sensor,
which is located in the front pipe. The heated oxygen
sensor indicates
to the engine control module the
amount of oxygen in the exhaust gas, and the engine
control module changes the air/fuel ratio to the engine
by
controlling the fuel injectors. The best air/fuel ratio
to minimize exhaust emissions is 14.7 to
1, which
allows the three way catalytic converter to operate
most efficiently. Because of the constant measuring
and adjusting
of the air/fuel ratio, the fuel injection
system
is called a "Closed Loop" system (Fig. 6E2-67).
2. Fuel injectors
1. Engine Control Module (ECMl
4. Catalytic converter
3. 0, sensor
Fig. 6E2-67
I
I

Page 813 of 1928

ISUZU TROOPER 1995 Workshop Manual MODES OF OPERATION
The Engine Control Module (ECM) uses voltage inputs
from several sensors to determine how much fuel to
give the engine. The fuel is delivered under one of
several condition

MODES OF OPERATION
The Engine Control Module (ECM) uses voltage inputs
from several sensors to determine how much fuel to
give the engine. The fuel is delivered under one of
several conditions, called "modes". All the modes are
controlled by the ECM and are described below.
Starting Mode
When the ignition is first turned "ON", the ECM turns
"ON" the fuel pump relay for two seconds, and the fuel
pump builds up pressure. The ECM also checks the
Engine
Coolant Temperature (ECT) sensor and the
Throttle Position Sensor, and the determines the
proper
air/fuel ratio for starting. This ranges from 1.5:1
-36·c (-33.F) to 14.7:1, at 94•c (201.F) ECT.
The ECM controls the amount of fuel delivered in the
starting mode by changing
how long the injector is
turned
"ON" and "OFF". The is done by "Pulsing" the
injectors
for very short times.
Clear Flood Mode
If the engine floods, it may be cleared by pushing the
accelerator pedal down all the way. The ECM then will
fixed air/fuel ratio 16.5:1. The ECM holds this injector
rate
as long as the throttle stays wide open. If the
throttle position becomes less than approximately
70%, the ECM returns to the starting mode.
Run Mode
The run mode has two conditions called "Open Loop"
and "Closed Loop"
"Open Loop"
When the engine is first started, and it is above 500
Rovolution Per Minute (rpm), the system goes into
"Open Loop" operation. IN "Open Loop," the ECM
ignores the signal from the heated oxygen sensor
(H02S), and calculates the air/fuel ratio based on
inputs
from the ECT sensor and manifold absolute
pressure sensors.
The system stays in
"Open Loop" until the following
conditions are met:
1. The H02S has varying voltage output, showing
that
it is hot enough to operate properly. (This
depends on temperature.)
2. The ECT sensor is above a specified temperature.
3. A specific amount of time has elapsed after
starting the engine.
"Closed Loop"
The specific values for the above conditions vary with
different engines, and are stored in the ECM. When
these conditions are met, the system goes into
"Closed
Loop"
operation. In "Closed Loop", the ECM calculates
the air/fuel ratio (injector on-time) based on the signal
from the H02S. This allows the air/fuel ratio to stay
very close to 14.7:1.
DRIVEABILITV AND EMISSIONS 6E2-117
Acceleration Mode
The ECM responds to rapid changes in throttle position
and air
flow, and provides extra fuel.
Deceleration Mode
The ECM responds to changes in throttle position and
air
flow, and reduces the amount of fuel. When
deceleration is very fast, the ECM can cut off fuel
completely
for short periods.
Battery Positive Voltage Correction Mode
When battery positive voltage is low, the ECM can
compensate
for a weak spark delivered by the ignition
control module by:
• Increasing injector pulse width.
• Increasing the idle rpm.
• Increasing ignition dwell time.
Fuel Cutoff Mode
The fuel injectors are shut "OFF" if engine speed
"exceed" 6880 rpm (DOHC) or6800 rpm (SOHC). This is
to prevent damage to engine. When engine speed is
below 6880 rpm (DOHC) or 6800 rpm (SOHC), the fuel
injectors are again pulsed at a normal mode.

Page 814 of 1928

ISUZU TROOPER 1995 Workshop Manual 6E2-118 DRIVEABILITV AND EMISSIONS
FUEL METERING SYSTEM COMPONENTS
The fuel metering system (Fig. 6E2-68) consists of the
following components:
• Fuel supply components (fuel tank, pump and

6E2-118 DRIVEABILITV AND EMISSIONS
FUEL METERING SYSTEM COMPONENTS
The fuel metering system (Fig. 6E2-68) consists of the
following components:
• Fuel supply components (fuel tank, pump and
lines).
• Fuel
pump electrical circuit.
• Fuel rail assembly, including:
-Fuel pressure control valve
• Throttle
body assembly, including:
-Idle Air Control valve
-Throttle Position Sensor
engine
sensors
• Fuel • :pump : ........
Fuel tank
Fig. 6E2-68
FUEL SUPPL V SYSTEM
The fuel supply is stored in the fuel tank. An electric
fuel
pump, located in the fuel tank with the gage
sending unit, pumps
fuel through an in-line fuel filter to
the
fuel rail assembly. The pump is designed to
provide
fuel at a pressure above the pressure needed
by the injectors. A fuel pressure control valve, an
integral part of the fuel rail assembly, keeps fuel
available
to the injectors at a controlled pressure.
Unused
fuel is returned to the fuel tank by a separate
line. See ENGINE FUEL (SECTION 6C) for replacement
procedures covering the fuel tank, fuel pump, in-line
filter
and fuel lines.
FUEL PUMP ELECTRICAL CIRCUIT
When the key is first turned "ON" without the engine
running, Engine
Control Module (ECM) will turn the fuel
pump relay "ON" for two seconds. This builds up the
fuel pressure quickly. lfthe engine is not started within
two seconds, the ECM will shut the fuel pump "OFF"
and wait until the engine starts. As soon as the engine
is cranked, the
ECM will turn the relay "ON" and run the
fuel pump.
An inoperative
fuel pump would cause a no start
condition. A
fuel pump which does not provide
enough pressure can
result in poor performance,
(refer to CHARTs A-5 and A-7).
FUEL RAIL ASSEMBL V
The fuel rail assembly (Fig. 6E2-69) is mounted to the
Inlet manifold, and performs several functions: It
positions the injectors in the cylinder head, it
distributes fuel evenly to the injectors, and it integrates
the
fuel pressure control valve into the fuel metering
system.
Fuel flow within the rail is shown in Fig. 6E2-
70.
Fig. 6E2-69
Fig. 6E2-70

Page 815 of 1928

ISUZU TROOPER 1995 Workshop Manual FUEL INJECTORS
The multipart fuel injection injector assembly is a
solenoid-operated device, controlled
by the Engine
Control Module (ECM), that meters pressurized fuel to
a single engine

FUEL INJECTORS
The multipart fuel injection injector assembly is a
solenoid-operated device, controlled
by the Engine
Control Module (ECM), that meters pressurized fuel to
a single engine cylinder.
The
ECM energizes the low impedance (2.0 ohms) for
DOHC or High impedance (12.2 ohms) for SOHC
solenoid to a normally closed ball valve. This allows
fuel
to flow into the top of the injector, past the ball
valve, and through a recessed
flow director plate at the
injector outlet (Fig. 6E2-71). The director plate has six
machined holes
that control the fuel flow, generating a
conical spray pattern
of finely atomized fuel at the
injector tip. Fuel
from the tip is directed at the intake
valve, causing
it to become further atomized and
vaporized before entering the combustion chamber.
An injector which is stuck partially open
would cause a
loss
of pressure after engine shut down. Also, an
extended crank times would be noticed on some
engines. Dieseling could also
occ!Jr because some fuel
could be delivered
to the engine after the ignition is
turned
"OFF".
FUEL INJECTOR DRIVER OPERATION
The method of turning the Fuel Injectors "ON" and
"OFF" is called a "Peak" and "Hold" Driver System.
The
ECM uses a transistor to "Peak" Injector to open it.
A second set
of Injector Drivers will "Hold" the Injectors
open for the calculated pulse width. The ECM has three
(3) Injector Drivers, they are labeled A, 8, and C inside
the
ECM. Injector Driver "A" is used to open the Injector
initially (Peak) and depending on available battery
positive voltage
Injector Drive "8" or "C" is used to
"Hold" the Injector for the amount of time necessary to
inject the proper amount of fuel into the cylinder. A
resistor module in part
of the Injector Driver circuits to
protect the Injector Drivers from high current (amps). If
one of the Driver circuits become "Open" the vehicle
will
not start. Diagnosis of the Injector driver circuits
are done
with Chart A-3 "Cranks But Won't Run" chart
in
SECTION 6E2-A of this service manual.
FUEL PRESSURE CONTROL VALVE
ASSEMBLY
The fuel pressure control valve is a diaphragm
operated relief valve
with fuel pump pressure on one
side and regulator spring pressure and intake manifold
absolute pressure on the other (Fig. 6E2-72).
The function
of the regulator is to maintain a constant
pressure differential across the injectors at all times.
The fuel pressure control valve compensates
for
engine load by increasing fuel pressure as engine
vacuum drops.
The fuel pressure control valve is mounted at the end
ofthe fuel rail, and is serviced as a complete assembly.
The system operates in
an acceptable pressure range
of 280 to 320 kPa (41 to 46 psi) with engine running.
If the pressure is too low, poor performance and a
DRIVEABILITV AND EMISSIONS 6E2-119
diagnostic trouble code 44 could result. If the pressure
is too high, excess odor and a diagnostic trouble code
45 could result.
CHART A-7 has information on diagnosing fuel
pressure conditions.
11. Fuel inlet
Fig. 6E2-71
1. Solenoid assembly
Spacer
and
guide assembly
. Ball valve
8. Cover-pressure regulator 1. Vacuum tube
7.
6.
Seal · 0-ring
Base assembly
Fuel
outlet fitting
Fig. 6E2-72

Page 816 of 1928

ISUZU TROOPER 1995 Workshop Manual 6E2 120 DRIVEABILITY AND EMISSIONS
THROTTLE BODY (TB) ASSEMBLY
The Throttle Body (TB) assembly is attached to the
intake manifold air
plenum, and is used to control air
flow into the engine

6E2 120 DRIVEABILITY AND EMISSIONS
THROTTLE BODY (TB) ASSEMBLY
The Throttle Body (TB) assembly is attached to the
intake manifold air
plenum, and is used to control air
flow into the engine, thereby controlling engine output
(Fig. 6E2-73). The TB within the TB is opened by the
driver through the accelerator controls. During engine
idle, the
TB is almost closed, and air flow control is
handled by the Idle Air Control (lAC) valve, described
below. To prevent
TB icing during cool weather
operation, engine
coolant is directed through a engine
coolant tube, part
of the TB, the engine coolant then
circulates through internal passageways around the
throttle bore and returns via the return engine coolant
tube.
The
TB also provides the location for mounting the
Throttle Position
Sensor. Vacuum ports the located at,
above or
below the throttle body to generate vacuum
signal needed
by various components.
Idle Air Control (lAC) Valve
Engine idle speed is controlled by the Engine Control
Module (ECM) through the Idle Air Control (lAC) valve
mounted on the
TB. The ECM sends voltage pulses to
the lAC motor windings causing the lAC valve pintle to
move "IN" or "OUT" a given distance (a step or count)
for each pulse. The pintle movement controls the
airflow around the TBs, which in turn, controls engine
idle speed.
• The "controlled" or desired idle speed for all
engine operating conditions is programmed into
the
calibration of the ECM. The programmed
engine speeds are based on engine coolant
temperature, park/neutral position switch status,
vehicle speed, battery positive voltage, and air
conditioning pressure (if equipped).
• The ECM "learns" the proper lAC valve positions to
achieve warm, stabilized idle speeds (revolution
per minute), desired
for the various conditions
(Park/Neutral position
or Drive, air conditioning
"ON" or "OFF", if equipped). This information is
stored in
ECM "Keep Alive" memories
(information
is retained after ignition is "OFF"). All
other lAC valve positioning is calculated based on
these
memory values.
As a
result, engine variations due to wear and
variations in
minimum TB position (within limits)
do not affect engine idle speeds. This system
provides correct idle control under
all conditions.
This also means
that disconnecting power to the
ECM can result in incorrect idle control or
necessity to partially depress the accelerator
pedal
when starting until the ECM relearns idle
control. Refer to note regarding clearing
memory
in "ECM and Sensors," Section "6E2-C1 ".
•
Engine idle speed is a function of total airflow into
the engine based on
lAC valve pintle position plus
TB opening plus calibrated vacuum loss through
accessories.
• The minimum TB position is set at the factory with
a stop screw. This setting allows enough air flow
by the TB to cause the lAC valve pintle to be
positioned a calibrated
number of steps (counts),
from the seat, during "controlled" idle operation.
The
minimum TB position setting on this engine
should not be considered the
"minimum idle
speed", as on other fuel injected engines. The
throttle stop
screw is covered with a plug at the
factory
following adjustment.
U7 CAUTION:
VI Do not attempt to remove the protective cap and
readjust the stop screw before
reviewi~g t~e
"Minimum TB Position Check", later m th1s
section. Misadjustment may result in damage to
the lAC valve or TB.
Fig. 6E2-73
2. Throttle body assembly
3. Throttle position sensor (TPS)
• The ECM normally resets the lAC valve pintle
position once during each ignition cycle,
when
vehicle speed increases above 35 miles per hour
on moderate acceleration. During the reset, the
ECM commands the lAC valve pintle to retract
completely, then move
"IN" to the seated position
(to establish the zero
count position), and then
back
out to the desired position. If, after the reset,
the
ECM is able to control the idle speed within the
calibrated count range, the
lAC valve will not be
reset again until the ignition has been turned
"OFF", the engine restarted and the car then
driven above 35 mile per hour.
If the ECM is not
able to control idle speed within the calibrated
count range after the first reset, the
ECM assumes
the
lAC valve pintle position is "lost", and enables
another reset
to occur. This will continue until the
pintle position is relearned.
• If the lAC valve is suspected as being the cause of
improper idle speed, perform a functional check of
the lAC valve (CHART C-2C) as described later in
this section.
-----------------------------'
•

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