Isuzu engine C22NE / 22LE / 20LE. Manual - part 117

DRIVEABILITY AND EMISSIONS  6E1-297

STARTING MODE

When the ignition is first turned ON, the ECM energizes the
fuel pump relay for two seconds to allow the fuel pump to build
up pressure. The ECM then checks the engine coolant
temperature (ECT) sensor and the throttle position (TP) 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.

THROTTLE BODY UNIT

The throttle body has a throttle plate to control the amount of
air delivered to the engine. The TP sensor and IAC valve are
also mounted on the throttle body.
Vacuum ports located behind the throttle plate provide the
vacuum signals needed by various components. Engine
coolant is directed through a coolant cavity in the throttle body
to warm the throttle valve and to prevent icing.

ELECTRONIC IGNITION SYSTEM

CRANKSHAFT POSITION (CKP)

SENSOR

The crankshaft position (CKP) sensor provides a signal used
by the engine control module (ECM) to calculate the ignition
sequence. The sensor initiates the 58X reference pulses which
the ECM uses to calculate RPM and crankshaft position. Refer
to Electronic Ignition System for additional information.

ELECTRONIC IGNITION

The electronic ignition system controls fuel combustion by
providing a spark to ignite the compressed air/fuel mixture at
the correct time. The provide optimum engine performance,
fuel economy, and control of exhaust emissions, the ECM
controls the spark advance of the ignition system. Electronic
ignition has the following advantages over a mechanical
distributor system:
• No moving parts.
• Less maintenance.
• Remote mounting capability.
• No mechanical load on the engine.
• More coil cool down time between firing events.
• Elimination of mechanical timing adjustments.
• Increased available ignition coil saturation time.

6E1-298  DRIVEABILITY AND EMISSIONS

IGNITION COILS

The all engines use 2 ignition coils, 1 per 2 cylinders. A two-
wire connector provides a 12-volt primary supply through the
15-amp ignition coil fuse.

IGNITION CONTROL

The ignition control (IC) spark timing is the ECM's method of
controlling the spark advance and the ignition dwell.
The IC spark advance and the ignition dwell are calculated by
the ECM using the following inputs:
• Engine speed.
• Crankshaft position (58X reference).
• Engine coolant temperature (ECT) sensor.
• Throttle position (TP) sensor.
• Vehicle speed (vehicle speed sensor).
• ECM and ignition system supply voltage.

IGNITION CONTROL ECM OUTPUT

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 X58 signal. In accordance with the X58 signal, ignition
coil driver determines the adequate ignition timing and also
cylinder number to ignite.
Ignition timing is determined the Coolant Temp., Intake Air
Temp., Engine Speed, Engine Load, knock Sensor Signal, etc.

ENGINE CONTROL MODULE (ECM)

The ECM is responsible for maintaining proper spark and fuel
injection timing for all driving conditions. To provide optimum
driveability and emissions, the ECM monitors the input signals
from the following components in order to calculate spark
timing:
• Engine coolant temperature (ECT) sensor.
• Intake air temperature (IAT) sensor.
• Throttle position sensor (TPS).
• Vehicle speed sensor (VSS).
• Crankshaft position (CKP) sensor.

DRIVEABILITY AND EMISSIONS  6E1-299

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 mixture 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 mixture 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, excessive gap, or
a cracked or broken insulator. If misfiring occurs before 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. Excessive 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 mixtures or poor
ignition system output may also be the cause. Refer to DTC 45.
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 excess
lubricating oil to enter the cylinder, particularly if the deposits
are heavier on the side of the spark plug facing the intake
valve.

6E1-300  DRIVEABILITY AND EMISSIONS

Excessive 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 excessive 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. Excessive 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 excessively lean fuel mixture.

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 extreme cases, exhaust 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
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.