relay ISUZU TROOPER 1995 Manual Online

6E2-86 DRIVEABILITY AND EMISSIONS
DIAGNOSTIC TROUBLE CODE (DTC) 45
HEATED OXYGEN SENSOR (H02S) CIRCUIT
(RICH
HEATED OXYGEN SENSOR (H02S) SIGNAL INDICATED)
Circuit Description:
The Engine Control Module (ECM) supplies a voltage of about .45 volt between terminals "83" and "82". (If
measured with a 10 megohm digital voltmeter, this may read as low as .32 volts.) The Heated Oxygen Sensor
(H02S)
varies the voltage within a range of about 1 volt, if the exhaust is rich, down through about .1 0 volt, if
exhaust is lean.
The sensor is like an open circuit and produces no voltage, when it is below about 360"C (600"F). An open sensor
circuit,
or cold sensor, cause "Open Loop" operation.
Test Description:
Numbers below refer to circled numbers ·on the diagnostic chart.
CD Diagnostic Trouble Code (DTC) 45 is set, when the H02S signal voltage is fixed above .1 0 volts (1 00 mV) under
the
following conditions:
• Throttle position sensor greater than 9.8%. • 02 Signal Voltage is les than 0.347 volts and
• No DTC 21 A/21 8 or 33A/338. greater than .547 volts.
•
The engine is running for longer than 180 • Temperature above 69.5"C (155"F).
seconds. • Integrator not at 128
• System is operating in "Closed Loop". • All of the above condition present for 50 sec.
Diagnostic Aids:
The DTC 45, or rich H02S signal, is most likely caused by one of the following:
• Fuel Pressure-System will go rich, if pressure is too high. The ECM can compensate for some increase.
However,
if it gets too high, a DTC 45 will be set. See Fuel System diagnosis CHART A-5.
• HEI Shielding-An open ground CKT BLK/GRN may result in EMI, or induced electrical "noise". The ECM
looks at this "noise" as reference pulses. The additional pulses result in a higher than actual engine speed
signal. The ECM then delivers too much fuel, causing system to go rich. Engine tachometer will also, show ~
higher than actual engine speed, which can help in diagnosing this problem.
• Evaporate emission canister purge-Check for fuel saturation. If full of fuel, check canister control and
hoses.
See evaporate emission canister purge, Section "C3".
• Manifold absolute pressure (MAP) sensor-An output that causes the ECM to sense a higher than normal
MAP (low vacuum) can causethesystemto go rich. Disconnecting the MAP sensor will allow the ECMtoseta
fixed value for the MAP sensor. Substitute a different MAP sensor, if the rich condition is gone, while the
sensor is disconnected.
• Throttle position sensor-An intermittent throttle position sensor output will cause the system to go rich,
due
to a false indication of the engine accelerating.
• 02 sensor contamination -Inspect H02S for silicone contamination from fuel, or use of improper RTV
sealant. The sensor may have a white, powdery coating and result in a high, but false signal voltage (rich
H02S signal indication). The ECM will then reduce the amount of fuel delivered to the engine, causing a
severe surge driveability problem.
• Exhaust gas recirculation -Valve sticking open at idle, usually accompanied by a rough idle, or stall
complaint, especially at idle. Refer to CHART C-7A to check exhaust gas recirculation system.
If DTC 45 is intermittent, refer to Section "6E2-8".
TRANSMISSION
HARNESS
CONNECTOR ,[BLK1
TRANSMISSION
HARNESS CONNECTOR !BLUE I I ,, BLK!GRN~E----r:......,-----"*----BLU
RED/BLU (MfT) ~ 1
1 1 RED
(BLUE) ~
PASSENGER Q SIDE FENDER
L T
BLU (AfT) L WHT/RED 1
R=+=+=:R l BLK!GRN -----BLK!GRN
BLK/YEL BLK!BLU
1
ENGINE
BLOCK Q TRANSMISSION HARNESS -CONNECTOR (BLUE) -
DRIVER'S SIDE REAR AT CYLINDER HEAD
10A BLK/GRN -~~EL PUMP RELAY
Fig. 6E2-48
ENGINE CONTROL MODULE(ECM)
02SGROUND REFERENCE 02S SIGNAL
ECM GROUNDS
ECM GROUNDS
..

6E2-90 DRIVEABILITY AND EMISSIONS
INTERMITTENTS
Definition: Problem may or may not turn "ON" the
"Check Engine" malfunction indicator lamp or store
Diagnostic
Trouble Code (DTC).
DO NOT use the DTC charts in "Engine Components/
Wiring Diagrams/Diagnostic
Charts," Section "6E2-A"
for intermittent problem. The fault must be present to
locate the problem. If a fault is intermittent, use of DTC
charts may result in replacement of good parts.
•
• Most intermittent problems are caused by faulty
electrical
connections or wiring. Perform careful
visual/physical
check as described at start of
"Symptoms," Section "6E2-B." Check for:
Poor mating
of the connector halves. or
terminal not fully seated in the connector body
(backed out).
Improperly formed or damaged terminal. All
connector
terminals in the problem circuit
should be carefully reformed or replaced to
insure proper contact tension.
Poor
terminal to wire connection. This
requires removing the
terminal from the
connector body to check. Refer to
SECTION 8
"Wiring Harness Service,"
If a visual/physical check does not find the cause
of the problem, the car can be driven with a
voltmeter connected to a suspected circuit. A
"Scan tool" can also be used to help detect
intermittent conditions. An abnormal
voltage, or
"Scan" tool reading, when the problem occurs,
indicates the
problem may be in that circuit. If the wiring
and connectors check
OK, and a DTC was
stored
for a circuit having a sensor, except for
DTC(s) 44 and 45, substitute a known good sensor
and recheck.
• Loss of DTC memory. To check, disconnect
throttle position (TP) sensor and idle engine until
"Check
Engine" malfunction indicator lamp comes
"ON". DTC 21 should be stored, and kept in
memory when ignition is turned "OFF". If not, the
Engine
Control Module (ECM) is faulty.
•
An intermittent "Check Engine" malfunction
indicator
lamp with no stored DTC may be caused
by:
Ignition coil shorted to ground and arcing at
spark
plug wires or plugs.
"Check
Engine" malfunction indicator lamp
wire to ECM shorted to ground.
Diagnostic
"test" terminal wire to ECM,
shorted to ground.
ECM grounds, refer to ECM wiring diagrams.
• Check for an electrical system interference caused
by a defective
relay, ECM driven solenoid, or
switch. They can cause a sharp electrical surge.
Normally, the problem will occur when the faulty
component is operated.
• Check for improper installation of electrical
options such as lights, 2 way radios, etc.
• Ignition control wires should be routed away from
spark plug wires, electronic ignition (EI) wires, El
housing, coil and generator. Ground wire from
ECM to El should have a good connection.
• If problem has not been found, refer to "ECM
Connector Symptom" charts at the end of
"Symptoms," Section "6E2-B."
HARD START
Definition: Engine cranks OK, but does not start for a
long time. Does eventually run, or may
start
but immediately dies.
PRELIMINARY CHECKS
• Perform the careful visual/physical checks as
described at start of "Symptoms," Section "6E2-
B".
•
Make sure the driver is using the correct starting
procedure.
SENSORS
• CHECK: Engine coolant temperature sensor using
a
"Scan tool", compare engine coolant
temperature with ambient temperature
on
cold engine. -
If engine coolant temperature
readings
is 5 degrees greater than or less than
ambient air temperature on a
cold
engine, check resistance in engine
coolant temperature sensor circuit
or
sensor itself. Compare engine coolant
temperature sensor resistance value
to the "Diagnostic Aids" chart on
DTC
14 chart.
• CHECK: Manifold absolute pressure sensor.
Check for flooding and/or correct sensor
for vehicle.
• CHECK: TP sensor for binding or a high TP sensor
voltage with the throttle closed (should
read between 0.54 volt and 1.25 volts.)

FUEL SYSTEM
• CHECK:
• CHECK:
• CHECK:
• CHECK:
• CHECK:
• CHECK:
Fuel pump relay operation-pump should
turn "ON" for 2 seconds when ignition is
turned
"ON". Use CHART A-5.
Fuel injectors are correct for the vehicle.
Fuel
pressure, use CHART A-7.
Contaminated
fuel.
Engine fuse (visual inspect).
A
faulty in-tank fuel pump check valve will
allow
the fuel in the lines to drain back to
the tank after engine is stopped. To check
for this condition, perform fuel system
diagnosis CHART A-7.
IGNITION SYSTEM
• CHECK: For proper ignition voltage output with
spark tester J26792 or equivalent (ST-
125).
DRIVEABILITY AND EMISSIONS 6E2-91
• CHECK: Spark plugs. Remove spark plugs, check
for wet plugs, cracks, wear, improper
gap, burned electrodes, or heavy
deposits. Repair
or replace as necessary.
• CHECK: Bare or shorted wires.
• CHECK: Loose ignition coil ground.
ADDITIONAL CHECKS
• CHECK: Idle air control operation-use CHART C-
2C.
• CHECK: Basic engine problem. Refer to ENGINE
MECHANICAL DIAGNOSIS (SECTION
6A).
• CHECK: Service Bulletins for calibration updates.
SURGES AND/OR CHUGGLES
Definition: Engine power variation under steady
throttle or cruise. Feels like the car speeds
up and
slows down with no change in the
acceleration pedal.
PRELIMINARY CHECKS
• Perform the careful visual checks as described at
start
of "Symptoms," Section "6E2-B."
•
Be sure driver understands transmission
operation, and air conditioning compressor
operation
as explained in the owner's manual.
SENSORS
• CHECK: Heated oxygen sensor (H02S). The
H02S should respond quickly to different
throttle position, if it does not, check the
H02S for silicon or other contaminations
from fuel, or use of improper RTV sealant.
The sensor may have a white, powdery
coating and result in a high but false
signal voltage
(rich heated H02S signal
indication). The engine control module
will
then reduce the amount of fuel
delivered
to the engine, causing a severe
driveability problem. Also, watch for
green glycol contamination or cracking.
FUEL SYSTEM
• NOTICE: To determine ifthe condition is caused by
a rich
or lean system, the car should be
driven at the speed of the complaint.
Monitoring block learn will help identify a
problem.
Lean -Block learn above 142. Refer to
"Diagnostic Aids" on facing page of
diagnostic trouble code 44.
Rich -L.T. Fuel Trim above 118. Refer to
"Diagnostic Aids" on facing page of
diagnostic trouble code 45.
• CHECK: Fuel pressure while condition exists. Use
CHART A-7.
• CHECK: In-line fuel filter. Replace if dirty or
plugged.
IGNITION SYSTEM
• CHECK: For proper ignition voltage output using
spark tester (ST-125) J26792
or
equivalent .
• CHECK: Spark plugs. Remove spark plugs, check
for wet plugs, cracks, wear, improper
gap, burned electrodes, or heavy
deposits. Repair
or replace as necessary.
Also, check condition of electronic
ignition and spark plug wires.
• CHECK: Ignition timing. Using "Scan tool".
ADDITIONAL CHECKS
• CHECK: Engine control module grounds for being
clean, tight and in their proper location.
• CHECK: Vacuum lines for kinks or leaks.
• CHECK: Exhaust gas recirculation -There should
be no exhaust gas recirculation at idle.
Refer to CHART C-7.
• CHECK: Generator output voltage. Repair if less
than 9 or more than 16 volts.

will not light when connected to the circuit. In some
cases, even an ordinary shop voltmeter
will not give an
accurate reading because its resistance is
too low.
Therefore, a 10 megohms input impedance digital
voltmeter is required to assure accurate voltage
readings.
The Engine
Control Module (ECM) controls output
circuits such as the fuel injectors, idle air control valve,
air conditioning clutch relay, etc. by controlling the
ground circuit through transistors
or a device called a
"quad-driver".
INFORMATION SENSORS
Engine Coolant Temperature (ECT) Sensor
(Fig. 6E2-51)
The Engine Coolant Temperature (ECT) Sensor is a
thermistor
(a resistor which changes value based on
temperature) mounted in the engine coolant stream.
Low ECT produces a high resistance (1 00,000 ohms at
-40.C/-40.F) while high temperature causes low
resistance (70 ohms at 130.C/266.F).
The ECM supplies a 5-volts signal to the ECT sensor
through a resistor in the
ECM and measures the
voltage. The voltage
will be high when the engine is
cold, and low when the engine is hot.
By measuring the voltage, the
ECM knows the ETC.
ECT affects most systems the ECM controls.
A failure in the
ECT sensor circuit should set a
Diagnostic Trouble Code
(DTC) 14. Remember, these
DTC(s) indicate a failure in the
ETC circuit, so proper
use
of the chart will lead to either repairing a wiring
problem or replacing the sensor, to properly repair a
problem.
1. Engine coolant temperature sensor
2. Harness connector to ECM
3. Locking tab
Fig. 6E2-51
Intake Air Temperature (IAT) Sensor
The Intake Air Temperature (IAT) sensor is a
thermistor, a resistor which changes
value based on
the temperature
of air entering the engine. Low
temperature produces a high resistance
(1 00,000
ohms at -4o·c/-40.F), while high temperature causes
low resistance (70 ohms at 130.C/266.F).
The ECM supplies a 5-volts signal to the sensor through
a resistor in the
ECM and measures the voltage. The
voltage
will be high when the intake air is cold, and low
DRIVEABILITV AND EMISSIONS 6E2-1 01
when the air is hot. By measuring the voltage, the ECM
knows the lAT.
The IAT sensor is also used to control spark timing and
delays exhaust gas recirculation when intake air is
cold.
A failure in the IAT sensor circuit should set a DTC 23.
Heated Oxygen Sensor (H02S) (Fig. 6E2-52)
The Heated Oxygen Sensor (H02S) is mounted in the
exhaust system where
it can monitor the Oxygen (02)
content of the exhaust gas stream. The 02 content in
the exhaust reacts
with the sensor to produce a voltage
output. This voltage ranges
from approximately .1 volt
(high 02-lean mixture) to .9 volt (low 02-rich mixture).
This voltage can
be measured with a digital voltmeter
having at
least 10 megohms input impedance. Use of
standard shop type voltmeters will result in very
inaccurate readings.
By monitoring the voltage
output ofthe H02S, the ECM
will know what fuel mixture command to give to the
injector
(lean mixture-low 02 voltage= rich command,
rich mixture-high
02 voltage= lean command).
The
H02S circuit, if open, should set a DTC 13. A
constant
low voltage in the sensor circuit should set a
DTC 44. While a constant high voltage in the circuit
should set a DTC 45. DTC(s) 44 and 45 could also be set
as a result of fuel system problems. See DTC charts for
conditions that can cause a lean or rich system.
The
H02S works in the same manner as the non-H02S
The exception is that battery positive voltage is
supplied to a heating unit that is part of the sensor
itself. This heater receives voltage
from the ECM's
main
relay circuit.
The heater
helps to heat up the H02S so the ECM can
start
controlling the fuel injection sooner for better fuel
emissions. There are no malfunction DTC(s) to detect if
the heater part of the sensor is working. To check the
heater, refer to "Functional
Check" in this section.
Fig. 6E2-52
~
\W

Park/Neutral Position (PNP) Switch (Auto Only)
The Park/Neutral position (PNP) switch indicates to the
Engine Control Module
(ECM) when the transmission
is in park, neutral
or drive. This information is used for
the exhaust gas recirculation, and the idle air control
valve operation.
NOTE:
• Vehicle
should not be driven with PNP switch
disconnected,
as idle quality will be affected and a
possible false diagnostic trouble code
(DTC) 24
(vehicle speed sensor).
DRIVEABILITY AND EMISSIONS 6E2-103
See DIAGNOSIS AND GENERAL SERVICE Section for
more information on the PNP switch. The PNP switch is
part
of the neutral/start and backup light switch
assembly mounted on the transmission.
See CHART C-
1 A for PNP switch check.
DIAGNOSIS
To read the DTC(s), use a "Scan tool" or ground the
diagnostic test terminal,
with the engine not running
and the ignition
"ON". The "Check Engine" malfunction
indicator lamp
will flash DTC 12 three times and then
flash each
DTC stored in memory three times. All
DTC(s) stored in memory will have been read when
DTC 12 is flashed again.
No new
DTC(s) can be stored when in the diagnostics
test mode (diagnostics lead grounded). This
eliminates confusion while the system is being
serviced.
To clear the
DTC(s) from memory:
• Ignition "OFF".
•
Disconnect main fuse located in the under hood
fuse/relay center near the battery.
Since the ECM can have a failure which may affect only
one circuit, following the diagnostic procedures in this
section
will determine which circuit has a problem and
where
it is.
If a diagnostic chart indicates thatthe ECM connections
or ECM is the cause of a problem, and the ECM is
replaced,
but does not correct the problem, one of the
following may be the reason.
• There is a problem with the ECM terminal
connections-The diagnostic chart will say ECM
connections or ECM. The terminals may have to
be removed from the connector in order to check
them properly.
• The ECM is not correct for the Vehicle-Ane
incorrect
ECM may cause a malfunction and may
set a DTC.
• The problem is intermittent -This means that
the problem is
not present at the time the system is
being checked.
In this case, refer to the
"Symptoms" portion of the manual and make a
careful physical inspection
of all portions of the
system involved.
• Shorted solenoid, relay coil, or harness
Solenoid and relays are turned "ON" and "OFF" by
the
ECM, using internal electronic switches called
"drivers".
Each driver is part of a group of four,
called "quad-drivers". Failure of one driver can
damage any other driver in the set. A
shorted solenoid, relay coil, or harness in a l-EFT­
SHCI
computer will not damage the ECM, but will
cause the circuit and controlled component to be
inoperative. When the circuit fault is not present or
has been repaired, the "quad-driver" will again
operate in a normal manner due to its fault
protected design. If a fault has been repaired in a
circuit controlled by a "quad-driver", the original
ECM should be reinstalled and the circuit checked
for proper operation. ECM replacement will not be
necessary if the repaired circuit or component now
operates correctly.
J 34636 or BT-8405 testers or equivalent provide a fast,
accurate means
of checking for a shorted coil or a short
to battery positive voltage.
• The replacement ECM may be faulty-After the
ECM is replaced, the system should be re-checked
for proper operation. If the diagnostic chart again
indicates the
ECM is the problem, substitute a
known good
ECM. Although this is a rare
condition,
it could happen.
ENGINE CONTROL MODULE (ECM)
A faulty ECM will be determined in the diagnostic
charts.
ELECTRONICALL V ERASABLE
PROGRAMMABLE READ
ONL V MEMORY
A faulty electrically erasable programmable read only
memory, which is part of the ECM, will set a DTC 51.
ENGINE CONTROL MODULE (ECM)
INPUTS
All of the sensors and input switches can be diagnosed
by the use
of "Scan tool".
Following is a short description of how the sensors and
switches can be diagnosed by the use
"Scan tool". The
"Scan tool" can also be used to compare the values for
a normal running engine with the engine you're
diagnosing.

6E2-1 08 DRIVEABILITV AND EMISSIONS
CHART C-1A
PARK/NEUTRAL POSITION (PNP} SWITCH DIAGNOSIS
(AUTO TRANSMISSION ONL
V}
Circuit Description:
The
Park/Neutral Position (PNP) switch contacts are a part of the Mode switch assembly. They are closed to
ground in park or neutral and open in drive ranges.
The Engine
Control Module (ECM) supplies voltage through a current limiting resistor to BLU/PNK wire and
senses a
closed switch when the voltage on BLU/PNK wire drops to less than one volt.
The ECM uses the PNP signal as one ofthe inputs to control idle air, vehicle speed sensor diagnostics, and exhaust
gas recirculation.
If BLU/PNK wire indicates PNP (grounded), while in drive range, the ECM would be inoperative, resulting in
possible detonation.
If BLU/PNK wire indicates drive (open), a dip in the idle may exist when the gear selector is moved into drive range.
Test Description:
Number(s)
below refer to circled number(s) on the diagnostic chart.
1. Checks for a closed switch to ground in park position. Different makes of "Scan tools" will read PNP differently.
Refer to tool operator's manual for type of display used for a specific tool.
2 To gain access to the wiring for the Diode, it will be necessary to remove the lower cover of the underhood
fuse/Relay center.
MODE SWITCH PART OF
INHIBITOR SWITCH TRANSMISSION ASSEMBLY CONNECTOR
_[ BLK +~•+1-------rt--BLU/BLK -{~ PNK/BLU
-BLU/BLK
l
TO STARTER
RELAY COIL
SIDE OF RELAY
DIODE E-1
ENGINE CONTROL MODULE(ECM)
~ BLU/PNK ~ P/N POSITION SIGNAL
LOCATED IN
UNDERHOOD
FUSE/RELAY
CENTER
Fig. 6E2-61
Ill

DRIVEABILITY AND EMISSIONS 6E2-1 09
CHART C-1A
PARK/NEUTRAL POSITION (PNP) SWITCH DIAGNOSIS
(AUTO TRANSMISSION ONLY)
CD • IGNITION "ON" ENGINE NOT RUNNING.
• "SCAN TOOL" INSTALLED.
"SCAN TOOL" SHOULD DISPLAY "PARK/NEUTRAL" POSITION
(PNP} WITH TRANSMISSION
IN PARK OR NEUTRAL?
AND "R·D-L" WITH TRANSMISSION IN ALL OTHER SHIFT
POSITIONS?
DOES
IT?
@ • REMOVE THE DIODE FROM THE UNDERHOOD FUSE/RELAY CENTER. • USE A DVM PROBE THE BLU/PINK WIRE.
SHOULD HAVE 12 VOLTS.
DOES IT?
• TEST LIGHT CONNECTED TO BATTERY POSITIVE SENSOR,
PROBE THE PNK/BLU WIRE AT THE DIODE CAVITY.
• TEST LIGHT SHOULD BE "ON" WITH TRANSMISSION IN PARK.
IS IT?
OPEN IN BLU/PNK WIRE OR FAULTY ENGINE CONTROL
MODULE.
OPEN
IN PNK/BLU WIRE OR MISADJUSTED PNP SWITCH OR FAULTY PNP SWITCH.

6E2-112 DRIVEABILITY AND EMISSIONS
CHART C-1E
POWER STEERING PRESSURE (PSP) SWITCH DIAGNOSIS
Circuit Description:
The Power Steering Pressure
(PSP) Switch is normally open to ground, and GRNIYEL wire will be near the battery
positive
voltage.
Turning the steering wheel increases power steering oil pressure and its load on an idling engine. The pressure
switch
will close before the load can cause an idle problem.
Closing
the switch causes GRN/YEL wire to read less than 1 volt. The Engine Control Module (ECM) will increase
the
idle air rate and disengage the air conditioning relay.
•
A pressure switch that will not close, or an open GRNIYEL wire, may cause the engine to stop, when power
steering loads are high.
• A switch that will not open or a GRNIYEL wire shorted to ground, may affect idle quality and will cause the air
conditioning
relay to be de-energized.
Test Description:
Numbers
below refer to circled numbers on the diagnostic chart.
CD Different makes of "Scan tools" may display the state of this switch in different ways. Refer to "Scan tool"
operator's manual to determine how this input is indicated.
® Checks to determine if GRNIYEL wire is shorted to ground.
@ This should simulate a closed switch.
POWER STEERING PRESSURE SWITCH ENGINE
CONTROL
MODULE(ECM)
I SIGNAL
r
BLU ---(~ BLU --+8 .. •f---BLU --{~ GRN/YEL ~ ~ B +
(LOCATED IN THE POWER
STEERING PUMP HIGH PASSENGERS CHASSIS PRESSURE LINE)
SIDE GROUND
FENDER
Fig. 6E2-65
•

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

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.