2004 ISUZU TF SERIES Fuel sensor

3.5L ENGINE DRIVEABILITY AND EMISSIONS 6E-53
Idle Air Control (IAC) Valve








Step
CoilAB CD
Coil A High
(EC M B13)On On
Coil A Low
(EC M B16)On On
Coil B High
(EC M B14)On On
Coil B Low
(EC M B17)On On

(IAC Valve Close Direction)
(IAC Valve Open Direction)



The idle air control valve (IAC) valve is two directional
and gives 2-way control. It has a stepping moto
r
capable of 256 steps, and also has 2 coils. With power
supply to the coils controlled steps by the engine control
module (ECM), the IAC valve's pintle is moved to adjus
t
idle speed, raising it for fast idle when cold or there is
extra load from the air conditioning or power steering.
By moving the pintle in (to decrease air flow) or out (to
increase air flow), a controlled amount of the air can
move around the throttle plate. If the engine speed is
too low, the engine control module (ECM) will retract the
IAC pintle, resulting in more air moving past the throttle
plate to increase the engine speed.
If the engine speed is too high, the engine control
module (ECM) will extend the IAC pintle, allowing less
air to move past the throttle plate, decreasing the
engine speed.

The IAC pintle valve moves in small step called counts.
During idle, the proper position of the IAC pintle is
calculated by the engine control module (ECM) based
on battery voltage, coolant temperature, engine load,
and engine speed.
If the engine speed drops below a specified value, and
the throttle plate is closed, the engine control module
(ECM) senses a near-stall condition. The engine control
module (ECM) will then calculate a new IAC pintle valve
position to prevent stalls. If the IAC valve is disconnected and reconnected with
the engine running, the idle speed will be wrong. In this
case, the IAC must be reset. The IAC resets when the
key is cycled "On" then "Off". When servicing the IAC, i
t
should only be disconnected or connected with the
ignition "Off".
The position of the IAC pintle valve affects engine start-
up and the idle characteristic of the vehicle.
If the IAC pintle is fully open, too much air will be
allowed into the manifold. This results in high idle
speed, along with possible hard starting and lean
air/fuel ratio.

Camshaft Position (CMP) Sensor








12
(1) Camshaft Position (CMP) Sensor
(2) EGR Valve


With the use of sequential multi-point fuel injection, a
hall element type camshaft position (CMP) is adopted to
provide information to be used in making decisions on
injection timing to each cylinder. It is mounted on the
rear of the left-hand cylinder head and sends signals to
the ECM.
One pulse is generated per two rotations of crankshaft.

6E-54 3.5L ENGINE DRIVEABILITY AND EMISSIONS
Crankshaft Position (CKP) Sensor





The crankshaft position (CKP) sensor, which sends a
signal necessary for deciding on injection timing to the
ECM, is mounted on the right-hand side of the cylinde
r
block.
The crankshaft has a 58 teeth press-fit timing disc, from
which the CKP sensor reads the position of the
crankshaft at all the times. It converts this to an
electrical signal, which it sends to the ECM.
Of the 58 teeth, 57 have a base with of 3°, and are
evenly spaced, but tooth No. 58 is 15° wide at its based
to serve as a timing mark, allowing the sensor to repor
t
the standard crankshaft position.
Using the 58 X signals per rotation and the timing-mark
signal sent by the CKP sensor, the ECM is able to
accurately calculate engine speed and crank position.
Also, the position of each cylinder is precisely known by
the ECM from signals sent by the camshaft position
(CMP) sensor, so the sequential multi-point fuel
injection can be controlled with accuracy.

The 58 X signals are converted by the ECM into a
retangle wave signal. This converted signal is sent from
the ECM terminal B12 to the tachometer and transfe
r
case control module (TCCM) terminal 15 (if 4WD
model).
Engine Coolant Temperature (ECT) Sensor




















The ECT sensor is a thermistor. A temperature
changes the resistance value. And it changes voltage.
In other words it measures a temperature value. It is
installed on the coolant stream. Low coolan
t
temperature produces a high resistance.
The ECM supplies 5 volts signal to the ECT senso
r
through resisters in the ECM and measures the voltage.
The signal voltage will be high when the engine
temperature is cold, and it will be low when the engine
temperature is hot.

Characteris tic of ECT Sens or
10 100 1000 10000 100000-3010 50 90130Temperature (

)
Resistance (Ω)

3.5L ENGINE DRIVEABILITY AND EMISSIONS 6E-55
Vehicle Speed Sensor (VSS)



The VSS is a magnet rotated by the transmission output
shaft. The VSS uses a hall element. It interacts with the
magnetic field treated by the rotating magnet. It outputs
pulse signal. The 12 volts operating supply from the
meter fuse.
Heated Oxygen (O2) Sensor




1
(1) Bank 1 Heated Oxygen Sensor (RH)






1
(1) Bank 2 Heated Oxygen Sensor (LH)

Each oxygen sensor consists of a 4-wire low
temperature activated zirconia oxygen analyzer elemen
t
with heater for operating temperature of 315C, and
there is one mounted on each exhaust pipe.
A constant 450millivolt is supplied by the ECM between
the two supply terminals, and oxygen concentration in
the exhaust gas is reported to the ECM as returned
signal voltage.
The oxygen present in the exhaust gas reacts with the
sensor to produce a voltage output. This voltage should
constantly fluctuate from approximately 100mV to
1000mV and the ECM calculates the pulse width
commanded for the injectors to produce the prope
r
combustion chamber mixture.
Low oxygen sensor output voltage is a lean mixture
which will result in a rich commanded to compensate.
High oxygen sensor output voltage is a rich mixture
which result in a lean commanded to compensate.
When the engine is first started the system is in "Open
Loop" operation. In "Open Loop", the ECM ignores the
signal from the oxygen sensors. When various
conditions (ECT, time from start, engine speed &
oxygen sensor output) are met, the system enters
"Closed Loop" operation. In "Closed Loop", the ECM
calculates the air fuel ratio based on the signal from the
oxygen sensors.

Heated oxygen sensors are used to minimize the
amount of time required for closed loop fuel control to
begin operation and allow accurate catalyst monitoring.
The oxygen sensor heater greatly decreases the
amount of time required for fuel control sensors to
become active.
Oxygen sensor heaters are required by catalyst monito
r
and sensors to maintain a sufficiently high temperature
which allows accurate exhaust oxygen content readings
further away from the engine.

6E-56 3.5L ENGINE DRIVEABILITY AND EMISSIONS
GENERAL DESCRIPTION FOR FUEL
METERING
The fuel metering system starts with the fuel in the fuel
tank. An electric fuel pump, located in the fuel tank,
pumps fuel to the fuel rail through an in-line fuel filter.
The pump is designed to provide fuel at a pressure
above the pressure needed by the injectors.
A fuel pressure regulator in the fuel rail keeps fuel
available to the fuel injectors at a constant pressure.
A return line delivers unused fuel back to the fuel tank.

The basic function of the air/fuel metering system is to
control the air/fuel delivery to the engine. Fuel is
delivered to the engine by individual fuel injectors
mounted in the intake manifold.
The main control sensor is the heated oxygen senso
r
located in the exhaust system. The heated oxygen
sensor reports to the ECM how much oxygen is in the
exhaust gas. The ECM changes the air/fuel ratio to the
engine by controlling the amount of time that fuel
injector is "On".
The best mixture to minimize exhaust emissions is 14.7
parts of air to 1 part of gasoline by weight, which allows
the 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.
The ECM monitors signals from several sensors in
order to determine the fuel needs of the engine. Fuel is
delivered under one of several conditions called
"mode". All modes are controlled by the ECM.

Acceleration Mode
The ECM provides extra fuel when it detects a rapid
increase in the throttle position and the air flow.

Battery Voltage Correction Mode
When battery voltage is low, the ECM will compensate
for the weak spark by increasing the following:

The amount of fuel delivered.

The idle RPM.

Ignition dwell time.

Clear Flood Mode
Clear a flooded engine by pushing the accelerator pedal
down all the way. The ECM then de-energizes the fuel
injectors. The ECM holds the fuel injectors de-
energized as long as the throttle remains above 80%
and the engine speed is below 800 RPM. If the throttle
position becomes less than 80%, the ECM again begins
to pulse the injectors "ON" and "OFF," allowing fuel into
the cylinders.

Deceleration Mode
The ECM reduces the amount of fuel injected when i
t
detects a decrease in the throttle position and the air
flow. When deceleration is very fast, the ECM may cu
t
off fuel completely for short periods.
Engine Speed/Vehicle Speed/Fuel Disable Mode
The ECM monitors engine speed. It turns off the fuel
injectors when the engine speed increase above 6400
RPM. The fuel injectors are turned back on when
engine speed decreases below 6150 RPM.

Fuel Cutoff Mode
No fuel is delivered by the fuel injectors when the
ignition is "OFF." This prevents engine run-on. In
addition, the ECM suspends fuel delivery if no reference
pulses are detected (engine not running) to preven
t
engine flooding.

Run Mode
The run mode has the following two conditions:

Open loop

Closed loop
When the engine is first started the system is in "open
loop" operation. In "open loop," the ECM ignores the
signal from the heated oxygen sensor (HO2S). I
t
calculates the air/fuel ratio based on inputs from the TP,
ECT, and MAF sensors.
The system remains in "open loop" until the following
conditions are met:

The HO2S has a varying voltage output showing
that it is hot enough to operate properly (this
depends on temperature).

The ECT has reached a specified temperature.


A specific amount of time has elapsed since
starting the engine.

Engine speed has been greater than a specified
RPM since start-up.
The specific values for the above conditions vary with
different engines and are stored in the programmable
read only memory (PROM). When these conditions are
met, the system enters "closed loop" operation. In
"closed loop," the ECM calculates the air/fuel ratio
(injector on-time) based on the signal from the HO2S.
This allows the air/fuel ratio to stay very close to 14.7:1.

3.5L ENGINE DRIVEABILITY AND EMISSIONS 6E-57
Starting Mode
When the ignition is first turned "ON," the ECM
energizes the fuel pump relay for two seconds to allo
w
the fuel pump to build up pressure. The ECM then
checks the engine coolant temperature (ECT) senso
r
and the throttle position sensor to determine the proper
air/fuel ratio for starting.
The ECM controls the amount of fuel delivered in the
starting mode by adjusting how long the fuel injectors
are energized by pulsing the injectors for very short
times.

Fuel Metering System Components
The fuel metering system is made up of the following
parts.

Fuel injector

Throttle Body

Fuel Rail

Fuel Pressure regulator

ECM

Crankshaft position (CKP) sensor

Camshaft position (CMP) sensor

Idle air control valve

Fuel pump

Fuel Injector
The sequential multi-port fuel injection fuel injector is a
solenoid operated device controlled by the ECM. The
ECM energizes the solenoid, which opens a valve to
allow fuel delivery.
The fuel is injected under pressure in a conical spray
pattern at the opening of the intake valve. Excess fuel
not used by the injectors passes through the fuel
pressure regulator before being returned to the fuel
tank.

Fuel Pressure Regulator
The fuel pressure regulator is a diaphragm-operated
relief valve mounted on the fuel rail with fuel pump
pressure on one side and manifold pressure on the
other side. The fuel pressure regulator maintains the
fuel pressure available to the injector at three times
barometric pressure adjusted for engine load. It may be
serviced separate.
If the pressure is too low, poor performance and a DTC
P0131, P0151, P0171, P0174, P1171 or P1174 will be
the result. If the pressure is too high, excessive odo
r
and/or a DTC P0132, P0152, P0172 or P0175 will be
the result. Refer to Fuel System Diagnosisfo
r
information on diagnosing fuel pressure conditions.
Fuel Rail
The fuel rail is mounted to the top of the engine and
distributes fuel to the individual injectors. Fuel is
delivered to the fuel inlet tube of the fuel rail by the fuel
lines. The fuel goes through the fuel rail to the fuel
pressure regulator. The fuel pressure regulato
r
maintains a constant fuel pressure at the injectors.
Remaining fuel is then returned to the fuel tank.







055RV009
Fuel Pump Electrical Circuit
When the key is first turned "ON," the ECM energizes
the fuel pump relay for two seconds to build up the fuel
pressure quickly. If the engine is not started within two
seconds, the ECM shuts the fuel pump off and waits
until the engine is cranked. When the engine is cranked
and the 58 X crankshaft position signal has been
detected by the ECM, the ECM supplies 12 volts to the
fuel pump relay to energize the electric in-tank fuel
pump.
An inoperative fuel pump will cause a "no-start"
condition. A fuel pump which does not provide enough
pressure will result in poor performance.

Camshaft Position (CMP) Sensor Signal
The ECM uses this signal to determine the position o
f
the number 1 piston during its power stroke, allowing
the ECM to calculate true sequential multiport fuel
injection. Loss of this signal will set a DTC P0341. If the
CMP signal is lost while the engine is running, the fuel
injection system will shift to a calculated sequential fuel
injection based on the last fuel injection pulse, and the
engine will continue to run. The engine can be restarted
and will run in the calculated sequential mode as long
as the fault is present, with a 1-in-6 chance of being
correct.

6E-58 3.5L ENGINE DRIVEABILITY AND EMISSIONS
GENERAL DESCRIPTION FOR
ELECTRONIC IGNITION SYSTEM IGNITION
COILS & CONTROL
A separate coil-at-plug module is located at each spark
plug.
The coil-at-plug module is attached to the engine with
two screws. It is installed directly to the spark plug by an
electrical contact inside a rubber boot.
A three way connector provides 12 volts primary supply
from the ignition coil fuse, a ground switching trigge
r
line from the ECM, and ground.
The ignition control spark timing is the ECM's method o
f
controlling the spark advance and the ignition dwell.
The ignition control spark advance and the ignition dwell
are calculated by the ECM using the following inputs.

Engine speed

Crankshaft position (CKP) sensor

Camshaft position (CMP) sensor

Engine coolant temperature (ECT) sensor

Throttle position sensor

Park or neutral position switch

Vehicle speed sensor

ECM and ignition system supply voltage

Based on these sensor signal and engine load
information, the ECM sends 5V to each ignition coil
requiring ignition. This signal sets in the powe
r
transistor of the ignition coil to establish a grounding
circuit for the primary coil, applying battery voltage to
the primary coil.
At the ignition timing, the ECM stops sending the 5V
signal voltage. Under this condition the power transistor
of the ignition coil is set off to cut the battery voltage to
the primary coil, thereby causing a magnetic field
generated in the primary coil to collapse.
On this moment a line of magnetic force flows to the
secondary coil, and when this magnetic line crosses the
coil, high voltage induced by the secondary ignition
circuit to flow through the spark plug to the ground.

Ignition Control ECM Output
The ECM provides a zero volt (actually about 100 mV to
200 mV) or a 5-volt output signal to the ignition control
(IC) module. Each spark plug has its own primary and
secondary coil module ("coil-at-plug") located at the
spark plug itself. When the ignition coil receives the
5-volt signal from the ECM, it provides a ground path fo
r
the B+ supply to the primary side of the coil-at -plug
module. This energizes the primary coil and creates a
magnetic field in the coil-at-plug module. When the
ECM shuts off the 5-volt signal to the ignition control
module, the ground path for the primary coil is broken.
The magnetic field collapses and induces a high voltage
secondary impulse which fires the spark plug and
ignites the air/fuel mixture.
The circuit between the ECM and the ignition coil is
monitored for open circuits, shorts to voltage, and
shorts to ground. If the ECM detects one of these
events, it will set one of the following DTCs:

P0351: Ignition coil Fault on Cylinder #1

P0352: Ignition coil Fault on Cylinder #2

P0353: Ignition coil Fault on Cylinder #3

P0354: Ignition coil Fault on Cylinder #4

P0355: Ignition coil Fault on Cylinder #5

P0356: Ignition coil Fault on Cylinder #6

Spark Plug
Although worn or dirty spark plugs may give satisfactory
operation at idling speed, they frequency fail at highe
r
engine speeds. Faulty spark plugs may cause poor fuel
economy, power loss, loss of speed, hard starting and
generally poor engine performance. Follow the
scheduled maintenance service recommendations to
ensure satisfactory spark plug performance. Refer to
Maintenance and Lubrication.
Normal spark plug operation will result in brown to
grayish-tan deposits appearing on the insulator portion
of the spark plug. A small amount of red-brown, yellow,
and white powdery material may also be present on the
insulator tip around the center electrode. These
deposits are normal combustion by-products of fuels
and lubricating oils with additives. Some electrode wea
r
will also occur. Engines which are not running properly
are often referred to as “misfiring." This means the
ignition spark is not igniting the air/fuel mixture at the
proper time.
Spark plugs may also misfire due to fouling, excessive
gap, or a cracked or broken insulator. If misfiring
occurs before the recommended replacement interval,
locate and correct the cause.

6E-62 3.5L ENGINE DRIVEABILITY AND EMISSIONS
GENERAL DESCRIPTION FOR EXHAUST
GAS RECIRCULATION (EGR) SYSTEM
Linear EGR Valve









060R200237
Legend
(1) ECM
(2) Linear EGR Valve
(3) Throttle
(4) Exhaust Manifold


The exhaust gas re-circulation (EGR) system is used to
reduce emission levels of oxides of nitrogen (NOx).
NOx emission levels are caused by a high combustion
levels by decreasing the combustion temperature.
The EGR valve feeds small amount of exhaust gas
back into the combustion chamber. The fuel/air mixture
will be diluted and combustion temperatures reduced.
Linear EGR valve Operation and Results o
f
Incorrect Operation
The linear EGR valve is designed to accurately supply
EGR to the engine independent of intake manifold
vacuum. The valve controls EGR flow from the exhaus
t
to the intake manifold through an orifice with a ECM
controlled pintle. During operation, the ECM controls
pintle position by monitoring the pintle position feedback
signal.

The linear EGR valve is activated under the following
conditions:

No DTC relating to the EGR.

Engine speed is between 1200 and 4375rpm.

Engine coolant temperature is between 20 and
100
.

Throttle position sensor output voltage is belo
w
3V.

Too mach EGR flow at idle, cruise or cold operation
may cause any of the following conditions to occur:

Engine stalls after a cold start.

Engine stalls at idle after deceleration.

Vehicle surges during cruise.

Rough idle.

Too little or no EGR flow may allow combustion
temperatures to get too high. This could cause:

Spark knock (detonation).

Emission test failure.

Poor fuel economy.

6E-70 3.5L ENGINE DRIVEABILITY AND EMISSIONS
Fuel Quality
Fuel quality is not a new issue for the automotive
industry, but its potential for turning on the MIL (“Check
Engine" lamp) with OBD systems is new.
Fuel additives such as “dry gas" and “octane
enhancers" may affect the performance of the fuel. The
Reed Vapor Pressure of the fuel can also create
problems in the fuel system, especially during the spring
and fall months when severe ambient temperature
swings occur. A high Reed Vapor Pressure could sho
w
up as a Fuel Trim DTC due to excessive canister
loading. High vapor pressures generated in the fuel
tank can also affect the Evaporative Emission
diagnostic as well.
Using fuel with the wrong octane rating for your vehicle
may cause driveability problems. Many of the majo
r
fuel companies advertise that using “premium" gasoline
will improve the performance of your vehicle. Mos
t
premium fuels use alcohol to increase the octane rating
of the fuel. Although alcohol-enhanced fuels may raise
the octane rating, the fuel's ability to turn into vapor in
cold temperatures deteriorates. This may affect the
starting ability and cold driveability of the engine.
Low fuel levels can lead to fuel starvation, lean engine
operation, and eventually engine misfire.
Non-OEM Parts
All of the OBD diagnostics have been calibrated to run
with OEM parts.
Aftermarket electronics, such as cellular phones,
stereos, and anti-theft devices, may radiate EMI into the
control system if they are improperly installed. This may
cause a false sensor reading and turn on the MIL
(“Check Engine" lamp).
Environment
Temporary environmental conditions, such as localized
flooding, will have an effect on the vehicle ignition
system. If the ignition system is rain-soaked, it can
temporarily cause engine misfire and turn on the MIL
(“Check Engine" lamp).
Vehicle Marshaling
The transportation of new vehicles from the assembly
plant to the dealership can involve as many as 60 key
cycles within 5Km miles of driving. This type o
f
operation contributes to the fuel fouling of the spark
plugs and will turn on the MIL (“Check Engine" lamp).

Poor Vehicle Maintenance
The sensitivity of OBD diagnostics will cause the MIL
(“Check Engine" lamp) to turn on if the vehicle is no
t
maintained properly. Restricted air filters, fuel filters,
and crankcase deposits due to lack of oil changes o
r
improper oil viscosity can trigger actual vehicle faults
that were not previously monitored prior to OBD. Poo
r
vehicle maintenance can not be classified as a
“non-vehicle fault", but with the sensitivity of OBD
diagnostics, vehicle maintenance schedules must be
more closely followed.
Severe Vibration
The Misfire diagnostic measures small changes in the
rotational speed of the crankshaft. Severe driveline
vibrations in the vehicle, such as caused by an
excessive amount of mud on the wheels, can have the
same effect on crankshaft speed as misfire.
Related System Faults
Many of the OBD system diagnostics will not run if the
ECM detects a fault on a related system or component.
One example would be that if the ECM detected a
Misfire fault, the diagnostics on the catalytic converte
r
would be suspended until Misfire fault was repaired. If
the Misfire fault was severe enough, the catalytic
converter could be damaged due to overheating and
would never set a Catalyst DTC until the Misfire faul
t
was repaired and the Catalyst diagnostic was allowed to
run to completion. If this happens, the customer may
have to make two trips to the dealership in order to
repair the vehicle.
Maintenance Schedule
Refer to the Maintenance Schedule.
Visual/Physical Engine Compartment
Inspection
Perform a careful visual and physical engine
compartment inspection when performing any
diagnostic procedure or diagnosing the cause of an
emission test failure. This can often lead to repairing a
problem without further steps. Use the following
guidelines when performing a visual/physical inspection:

Inspect all vacuum hoses for punches, cuts,
disconnects, and correct routing.

Inspect hoses that are difficult to see behind othe
r
components.

Inspect all wires in the engine compartment fo
r
proper connections, burned or chafed spots, pinched
wires, contact with sharp edges or contact with ho
t
exhaust manifolds or pipes.