2004 ISUZU TF SERIES engine

6E–54 ENGINE DRIVEABILITY AND EMISSIONS
GENERAL DESCRIPTION FOR ELECTRIC
IGNITION SYSTEM
The engine use two ignition coils, one per two cylinders.
A two wire connector provides a battery voltage primary
supply through the ignition fuse.
The ignition control spark timing is the ECM’s method of
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
Engine coolant temperature (ECT) sensor
Throttle position sensor
Vehicle speed sensor
ECM and ignition system supply voltage
Ignition coil works to generate only the secondary
voltage be receiving the primary voltage from ECM.
The primary voltage is generated at the coil driver
located in the ECM. The coil driver generate the primary
voltage based on the crankshaft position signal. In
accordance with the crankshaft position signal, ignition
coil driver determines the adequate ignition timing and
also cylinder number to ignite.
Ignition timing is determined the coolant temperature,
intake air temperature, engine speed, engine load,
knock sensor signal, etc.
Spark Plug
Although worn or dirty spark plugs may give satisfactory
operation at idling speed, they frequently fail at higher
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 wear
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 mix ture at the
proper time. While other ignition and fuel system causes
must also be considered, possible causes include
ignition system conditions which allow the spark voltage
to reach ground in some other manner than by jumping
across the air gap at the tip of the spark plug, leaving
the air/fuel mix ture unburned. Misfiring may also occur
when the tip of the spark plug becomes overheated and
ignites the mixture before the spark jumps. This is
referred to as “pre-ignition.”
Spark plugs may also misfire due to fouling, ex cessive
gap, or a cracked or broken insulator. If misfiring occursbefore the recommended replacement interval, locate
and correct the cause.
Carbon fouling of the spark plug is indicated by dry,
black carbon (soot) deposits on the portion of the spark
plug in the cylinder. Ex cessive idling and slow speeds
under light engine loads can keep the spark plug
temperatures so low that these deposits are not burned
off. Very rich fuel mix tures or poor ignition system output
may also be the cause. Refer to DTC P1167.
Oil fouling of the spark plug is indicated by wet oily
deposits on the portion of the spark plug in the cylinder,
usually with little electrode wear. This may be caused by
oil during break-in of new or newly overhauled engines.
Deposit fouling of the spark plug occurs when the
normal red-brown, yellow or white deposits of
combustion by-products become sufficient to cause
misfiring. In some cases, these deposits may melt and
form a shiny glaze on the insulator around the center
electrode. If the fouling is found in only one or two
cylinders, valve stem clearances or intake valve seals
may be allowing ex cess lubricating oil to enter the
cylinder, particularly if the deposits are heavier on the
side of the spark plug facing the intake valve.
Ex cessive gap means that the air space between the
center and the side electrodes at the bottom of the
spark plug is too wide for consistent firing. This may be
due to improper gap adjustment or to ex cessive wear of
the electrode during use. A check of the gap size and
comparison to the gap specified for the vehicle in
Maintenance and Lubrication will tell if the gap is too
wide. A spark plug gap that is too small may cause an
unstable idle condition. Ex cessive gap wear can be an
indication of continuous operation at high speeds or
with engine loads, causing the spark to run too hot.
Another possible cause is an ex cessively lean fuel
mixture.

ENGINE DRIVEABILITY AND EMISSIONS 6E–55
Low or high spark plug installation torque or improper
seating can result in the spark plug running too hot and
can cause excessive center electrode wear. The plug
and the cylinder head seats must be in good contact for
proper heat transfer and spark plug cooling. Dirty or
damaged threads in the head or on the spark plug can
keep it from seating even though the proper torque is
applied. Once spark plugs are properly seated, tighten
them to the torque shown in the Specifications Table.
Low torque may result in poor contact of the seats due
to a loose spark plug. Over tightening may cause the
spark plug shell to be stretched and will result in poor
contact between the seats. In ex treme cases, ex haust
blow-by and damage beyond simple gap wear may
occur.
Cracked or broken insulators may be the result of
improper installation, damage during spark plug re-
gapping, or heat shock to the insulator material. Upper
insulators can be broken when a poorly fitting tool is
used during installation or removal, when the spark plug
is hit from the outside, or is dropped on a hard surface.
Cracks in the upper insulator may be inside the shell
and not visible. Also, the breakage may not cause
problems until oil or moisture penetrates the crack later.A broken or cracked lower insulator tip (around the
center electrode) may result from damage during re-
gapping or from “heat shock” (spark plug suddenly
operating too hot).
Damage during re-gapping can happen if the gapping
tool is pushed against the center electrode or the
insulator around it, causing the insulator to crack.
When re-gapping a spark plug, make the adjustment
by bending only the ground side terminal, keeping the
tool clear of other parts.
“Heat shock” breakage in the lower insulator tip
generally occurs during several engine operating
conditions (high speeds or heavy loading) and may
be caused by over-advanced timing or low grade
fuels. Heat shock refers to a rapid increase in the tip
temperature that causes the insulator material to
crack.
Spark plugs with less than the recommended amount of
service can sometimes be cleaned and re-gapped, then

6E–56 ENGINE DRIVEABILITY AND EMISSIONS
returned to service. However, if there is any doubt about
the serviceability of a spark plug, replace it. Spark plugs
with cracked or broken insulators should always be
replaced.

ENGINE DRIVEABILITY AND EMISSIONS 6E–57
GENERAL DESCRIPTION FOR
EVAPORATIVE EMISSION SYSTEM
EVAP Emission Control System Purpose
The basic evaporative emission control system used on
the charcoal canister storage method. The method
transfers fuel vapor from the fuel tank to an activated
carbon (charcoal) storage devise to hold the vapors
when the vehicle is not operating.
The canister is located on the rear ax le housing by the
frame cross-member.
When the engine is running, the fuel vapor is purged
from the carbon element by intake air flow and
consumed in the normal combustion process.
EVAP Emission Control System Operation
The EVAP canister purge is controlled by a solenoid
valve that allows the manifold vacuum to purge the
canister. The engine control module (ECM) supplies a
ground to energize the solenoid valve (purge on). The
EVAP purge solenoid control is pulse-width modulated
(PWM) (turned on and off several times a second). The
duty cycle (pulse width) is determined by engine
operating conditions including load, throttle position,
coolant temperature and ambient temperature. The duty
cycle is calculated by the ECM. the output is
commanded when the appropriate conditions have
been met. These conditions are:
The engine is fully warmed up.
The engine has been running for a specified time.
The IAT reading is above 10°C (50°F).
Purge/Vacuum Hoses. Made of rubber compounds,
these hoses route the gasoline fumes from their
sources to the canister and from the canister to the
intake air flow.
EVAP Canister. Mounted on a bracket ahead of the
fuel tank, the canister stores fuel vapors until the
ECM determined that engine conditions are right for
them to be removed and burned.
Poor idle, stalling and Poor driveability can be caused
by:
A malfunctioning purge solenoid.
A damaged canister.
Hoses that are split, cracked, or not connected
properly.
System Fault Detection
The EVAP leak detection strategy is based on applying
vacuum to the EVAP system and monitoring vacuum
decay. At an appropriate time, the EVAP purge solenoid
is turned “ON,” allowing the engine vacuum to draw a
small vacuum on the entire evaporative emission
system.
After the desired vacuum level has been achieved, the
EVAP purge solenoid is turned “OFF,” sealing the
system. A leak is detected by monitoring for a decrease
in vacuum level over a given time period, all other
variables remaining constant.
If the desired vacuum level cannot be achieved in the
test described above, a large leak or a faulty EVAP
purge control solenoid valve is indicated.
Leaks can be caused by the following conditions:
Missing or faulty fuel cap
Disconnected, damaged, pinched, or blocked EVAP
purge line
Disconnected, damaged, pinched, or blocked fuel
tank vapor line
Disconnected or faulty EVAP purge control solenoid
valve
Open ignition feed circuit to the purge solenoid (1) Purge Solenoid Valve
(2) From Canistor to Purge Solenoid
(3) From Purge Solenoid to Intake
(1) Canistor
(2) Air Separator
132
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6E–58 ENGINE DRIVEABILITY AND EMISSIONS
Damaged EVAP canister
Leaking fuel sender assembly O-ring
Leaking fuel tank or fuel filler neck
The ECM supplies a ground to energize the purge
control solenoid valve (purge “ON” ). The EVAP purge
control is turned “ON” and “OFF,” several times a
second. The duty cycle (pulse width) is determined by
engine operating conditions including load, throttle
position, coolant temperature and ambient temperature.
The duty cycle is calculated by the ECM and the output
is commanded when the appropriate conditions have
been met.
The system checks for conditions that cause the EVAP
system to purge continuously by commanding the EVAP
purge solenoid “OFF”, EVAP purge solenoid duty ratio
“0%”. If fuel tank vacuum level increases during the test,
a continuous purge flow condition is indicated. This can
be caused by the following conditions:
EVAP purge solenoid leaking
EVAP purge and engine vacuum lines switched at the
EVAP purge control solenoid valve
EVAP purge control solenoid valve driver circuit
grounded

ENGINE DRIVEABILITY AND EMISSIONS 6E–59
POSITIVE CRANKCASE VENTILATION
(PCV) SYSTEM
Crankcase Ventilation System Purpose
The crankcase ventilation system is used to consume
crankcase vapors in the combustion process instead of
venting them to the atmosphere. Fresh air from the
throttle body is supplied to the crankcase and mixed
with blow-by gases. This mix ture is then passed through
the positive crankcase ventilation (PCV) port into the
intake manifold.
While the engine is running, ex haust gases and small
amounts of the fuel/air mix ture escape past the piston
rings and enter the crankcase. these gases are mixed
with clean air entering through a tube from the air intake
duct.
During normal, part-throttle operation, the system is
designed to allow crankcase gases to flow through the
PCV hose into the intake manifold to be consumed by
normal combustion.
A plugged positive crankcase ventilation port or PCV
hose may cause the following conditions:
Rough idle.
Stalling or slow idle speed.
Oil leaks.
Sludge in the engine.
A leaking PCV hose would cause:
Rough idle.
Stalling.
High idle speed.

6E–60 ENGINE DRIVEABILITY AND EMISSIONS
A/C CLUTCH DIAGNOSIS
A/C Clutch Circuit Operation
A 12-volt signal is supplied to the A/C request input of
the ECM when the A/C is selected through the A/C
control switch.
The A/C compressor clutch relay is controlled through
the ECM. This allows the ECM to modify the idle air
control position prior to the A/C clutch engagement for
better idle quality. If the engine operating conditions are
within their specified calibrated acceptable ranges, the
ECM will enable the A/C compressor relay. This is done
by providing a ground path for the A/C relay coil within
the ECM. When the A/C compressor relay is enabled,
battery voltage is supplied to the compressor relay is
enabled, battery voltage is supplied to the compressor
clutch coil.
The ECM will enable the A/C compressor clutch
whenever the engine is running and the A/C has been
requested. The ECM will not enable the A/C
compressor clutch if any of the following conditions are
met:
The engine speed is greater than 6000 RPM.
The ECT is greater than 122°C (251°F).
The throttle is more than 95% open.
A/C Clutch Circuit Purpose
The A/C compressor operation is controlled by the
engine control module (ECM) for the following reasons:
It improves idle quality during compressor clutch
engagement.
It improves wide open throttle (WOT) performance.
It provides A/C compressor protection from operation
with incorrect refrigerant pressures.
The A/C electrical system consists of the following
components:
The A/C control switch.
The A/C refrigerant pressure switches.
The A/C compressor clutch.
The A/C compressor clutch relay.
The ECM.
A/C Request Signal
This signal tells the ECM when the A/C mode is
selected at the A/C control switch. The ECM uses this
input to adjust the idle speed before turning on the A/C
clutch. The A/C compressor will be inoperative if this
signal is not available to the ECM.
Refer to A/C Clutch Circuit Diagnosis for A/C wiring
diagrams and diagnosis for the A/C electrical system.

ENGINE DRIVEABILITY AND EMISSIONS 6E–61
ISUZU STRATEGY BASED DIAGNOSTICS
Overview
As a retail service technician, you are part of the ISUZU
service team. The team goal is FIX IT RIGHT THE
FIRST TIME for the satisfaction of every customer. You
are a very important member of the team as you
diagnose and repair customer vehicles.You have max imum efficiency in diagnosis when you
have an effective, organized plan for your work.
Strategy Based Diagnostics (refer to Figure 1) provides
you with guidance as you create and follow a plan of
action for each specific diagnostic situation.
STRATEGY BASED DIAGNOSTICS CHART