COMPETENCY BASED LEARNING MATERIAL

Sector: AUTOMOTIVE LAND TRANSPORT

Qualification: Automotive Servicing NC II

Unit of Competency: Service Ignition System

Module Title: Servicing Ignition System

IGAMA COLLEGES FOUNDATION, INC.

Badoc, Ilocos Norte

[Type text]
 HOW TO USE THIS COMPETENCY BASED LEARNING MATERIAL

Welcome to the Module “Servicing Ignition System”. This module

contains training materials and activities for you to complete.

The unit of competency “Service Ignition System” contains the

knowledge, skills and attitudes required for an Automotive Servicing
course. This is one of the common modules for National Certificate
level II (NC II).

You are required to go through a series of learning activities in order

to complete each of the learning outcomes of the module. In each
learning outcome there are Information Sheets and Job Sheets
(Reference Materials for further reading to help you better understand
the required activities. Follow these activities on your own and answer
the self-check at the end of each learning activity.

If you have questions, don’t hesitate to ask your facilitator for

assistance.

Recognition of Prior Learning (RPL)

You may already have some or most of the knowledge and skills
covered in this module because you have:
 been working for some time
 already completed training in this area.

If you can demonstrate to your trainer that you are competent in a

particular skill or skills, talk to him/her about having them formally
recognized so you don’t have to do the same training again. If you
have a qualification or Certificate of Competency from previous
trainings show it to your trainer. If the skills you acquired are still
current and relevant to this module, they may become part of the
evidence you can present for RPL. If you are not sure about the
currency of your skills, discuss this with your trainer.

After completing this module ask your trainer to assess your

competency. The result of your assessment will be recorded in your
competency profile. All the learning activities are designed for you to
complete at your own pace.

In this module you will find the activities for you to complete and at
the back are the relevant information sheets for each learning
outcome. Each learning outcome may have more than one learning
activity.

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 At the end of this module is a Trainee Record Book. Use this book to
record important dates, jobs undertaken and other workplace events that
will assist you in providing further details to your trainer or an assessor. A
Certificate of Achievement is provided for you by your trainer to
accomplish once you complete the module.

This module is prepared to help you achieve the required competency

in servicing ignition system. This will be the source of information that will
enable you to acquire the knowledge and skills in this particular trade
independently at your own pace or with minimum supervision or help from
your trainer.

- Talk to your trainer and agree on how you will both organize the
training of this unit. Read through the learning guide carefully. It is
divided into sections which cover all the skills and knowledge you
need to successfully complete this module.
- Work through all the information and complete the activities in each
section and complete the self-check. Suggested references are
included to supplement the materials provided in this module.
- Most probably your trainer will also be your supervisor or manager.
He/she is there to support you and show you the correct way to do
things. Ask for help.
- Your trainer will tell you about the important things you need to
consider when you are completing activities and it is important that
you listen and take notes.
- Talk to more experienced work mates and ask for their guidance.
- Use the self-check questions at the end of each section to test your
own progress.
- When you are ready, ask your trainer to watch you perform the
activities outlined in the learning guide.
- As you work through the activities, ask for written feedback on your
progress from your trainer. After completing each element, ask
your trainer to mark on the report that you are ready for
assessment.
- When you have completed this module (or several modules) and
feel confident that you have had sufficient practice your trainer will
arrange an appointment with you to assess you. The result of your
assessment will be recorded in your Competency Achievement
Record.

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 MODULE CONTENT

QUALIFICATION : AUTOMOTIVE SERVICING NC II

UNIT OF COMPETENCY : SERVICE IGNITION SYSTEM

MODULE TITLE : SERVICING IGNITION SYSTEM

MODULE DESCRIPTOR:

This module contains information and practices involved in checking

the ignition system of a vehicle. It includes instructions on how to check up
an ignition system prior to troubleshooting.

You need to complete this module before you can actually start the
engine, since this part is the primary system that lets the engine run.

LEARNING OUTCOMES:

At the end of this module you will be able to:

 Identify and explain the function of the ignition system components

 Check ignition coil, ballast resistor, high tension cable resistance
 Check distributor assembly

ASSESSMENT CRITERIA:

 Ignition system components are identified

 Functions of the ignition system are understood
 Standard clearance and resistance of ignition system components
are determined
 The operating principle of the ignition system is explained
 VOM is properly used
 The specified resistance value is obtained from the service manual
 Procedure in checking resistance is observed in accordance with the
manual of instructions
 Distributor terminal and rotor tips are cleaned and lubricated
 Rotor and distributor cap are checked for cracks / current leakage
 The condenser is tested by charged and discharged process
 Dwell angle is adjusted / set in accordance with the manual of
specifications and instructions

 Cam lube is checked for wear

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  Rotor rotation is determined
 Advance mechanism operation is checked in accordance with the
manual of instructions

PRE-REQUISITE: Basic and Common Competencies

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LEARNING OUTCOME #1: IDENTIFY AND EXPLAIN THE FUNCTION OF
IGNITION SYSTEM COMPONENTS.

CONTENTS:
 Parts and function of ignition system components
 Testing and measurement procedures

ASSESSMENT CRITERIA:

 Ignition system construction and operation are identified and

explained.
 Ignition system troubles are identified and possible remedies are
explained.

CONDITIONS:
Trainees must be provided with the following:

 Engine mock-up
 Spark plug
 Contact point
 Ignition switch
 Battery
 Distributor
 Mock-up
 Ballast/resistor
 VOM
 Engine analyzer

ASSESSMENT METHODS:

 Interview
 Written examination
 Practical demonstration
 Direct observation

LEARNING EXPERIENCES
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Learning Outcome 1 : Identify and explain the functions of ignition system
components
LEARNING ACTIVITIES SPECIAL INSTRUCTIONS

Read Information Sheet #9.1.1: “Contact Point

Ignition System”

Compare answers with the

answer key. You are required
to get all answers correct. If
Answering self-check 9.1.1 not, read the information
sheets again to answer all
questions correctly.

Read Information Sheet #9.1.2: “Components in The trainer evaluates your

contact-point ignition system” and Perform job performance
sheet 9.1.1 “Identifying parts & components of
the ignition system”

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 INFORMATION SHEET 9.1.1

CONTACT POINT IGNITION SYSTEM

PURPOSE OF IGNITION SYSTEM

The purpose of the ignition system is to ignite the compressed air-fuel

mixture in the engine combustion chambers. This should occur at the proper
time for combustion to begin. To start combustion, the ignition system
delivers an electric spark that jumps a gap at the combustion-chamber ends
of the spark plugs. The heat from this arc ignites the compressed air-fuel
mixture. The mixture burns, creating pressure that pushes the pistons down
the cylinders so the engine runs. The ignition system may be either a
contact-point ignition system or an electronic ignition system.

PRODUCING THE SPARK

The ignition system consists of

two separate but related circuits:
the low-voltage primary circuit
and the high-voltage secondary
circuit. The ignition coil (Fig. 1)
has two windings. The primary
winding of a few hundred turns of
heavy wire is part of the primary
circuit.

The secondary winding in many

thousand turns of fine wire is part
of the secondary circuit, When Fig 1. Schematic diagram of the primary circuit in
the contact-point ignition system (ATW).
the ignition key is ON and the
contact points closed, current
flows through the primary
winding (Fig. 1). This produces a
magnetic field around the
primary windings in the coil.

When the contact points open, current flow stops and the magnetic field
collapse. As it collapses, it cuts across the thousands of turns of wire in the
coil secondary winding.

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This produces a voltage in each turn. These add together to produce the high
voltage delivered through the secondary circuit to the spark plug (Fig. 5).

SPARK PLUG HEAT RANGE AND REACH

Spark plugs are made in different

heat ranges (Fig. 2). The heat
range indicates how fast the plug
transfers heat from the
combustion chamber to the
cylinder head. This is primarily
determined by the length of the
lower insulator. The longer the
head path, the hotter the plug will
run. A short path transfers the
heat faster so the plug runs
cooler.

Sooty deposits accumulate on the

firing end of the spark plug if it
runs too cold. The end does not
get hot enough to burn away the
deposits. Then the high-voltage
surges short across the deposits
instead of jumping the spark-plug
gap. A plug that runs too hot
burns away the electrodes more
rapidly. This can widen the gap so
much that the spark cannot jump
it and miss occurs.
Figure 2. Heat range and reach of spark plugs.
The longer the heat path, as indicated by arrows,
Spark plug reach is the distance the hotter the plug runs. (AC Spark plug Division
from the shell gasket seat (or top of General Motors Corporation)
of the tapered seat to the end of
the threads. If the reach is too
long, the plug electrodes too far
into the combustion chamber The
plug could interfere with moisture
turbulence or be struck by valve
or piston. A plug that does not
reach far enough fail to will fail to
ignite the mixture properly. The
recommended spark plugs for an
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engine have the correct reach.

SELF-CHECK 9.1.1
I. Multiple Choice Test

Instruction: Select the best answer to each question

1. The ignition system performs all the following jobs except

a. controls the compression pressure
b. produces the spark that jumps the spark-plug gap
c. ignites the compressed air-fuel mixture
d. delivers the spark at the proper time

2. The contact-point distributor has two major jobs

a. to advance and retard spark
b. to distribute the high voltage surges and switch the current
to the coil on and off
c. to distribute the battery voltage and switch the current to
the spark plugs on and off
d. to provide centrifugal advance and vacuum advance

3. Technician A says the spark occurs when the contact points

open. Technician B says the spark occurs when the coil
magnetic field collapses. Who is right?
a. A only
b. B only
c. both A and B
d. neither A nor B

4. Cross-firing may be caused by all the following except

a. wet distributor cap or rotor
b. defective insulation on secondary cables
c. improper routing of spark-plug cables
d. a fouled spark-plug

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 ANSWER KEY 9.1.1

I.
1. a
2. b
3. c
4. d

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 INFORMATION SHEET 9.1.2

COMPONENTS IN CONTACT-POINT IGNITION SYSTEM

The ignition system (Fig. 3) includes the battery, ignition switch, ignition
coil, ignition distributor (with contact points and condenser), secondary
wiring, and spark plugs.

Figure 3. Components in the contact-point ignition system (Ford Motors Company)

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1. IGNITION SWITCH The ignition switch
connects the ignition coil to the battery
when the ignition key is ON. When the key
is turned to START, the starting motor
cranks the engine for starting.

2. IGNITION COIL The ignition coil (Fig. 4) is

a step-up transformer that raises the
battery voltage to a high voltage that may
reach 25,000 volts. In some electronic
ignition systems, the voltage may go up to
47,000 volts or higher. The high voltage
causes sparks to jump the gap at the
spark plugs.

Fig.4 Ignition coil, cut away to show the

windings. (Delco-Remy Division of General
Motors Corporation)

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3. IGNITION DISTRIBUTOR The ignition
distributor does two jobs. First, it has a set
of contact points or breaker points (lower
right) that work as a fast-acting switch.
When the points close, current flows
through the coil, When the points open,
the current flow stops and the coil produce
a high-voltage surge. A condenser
connects across the points. It aids in the
collapse of the magnetic field and helps
reduce arcing that burns away the points.

Fig. 5 Ignition distributor with vacuum-

advance unit and cap (Delco-Remy Division
of General Motors Corporation)

Second, the distributor distributes the

high-voltage surges to the spark plugs in
the correct firing order. A coil wire delivers
the high-voltage from the coil to the
center terminal of the distributor cap.
Inside the cap, a rotor (Fig. 6) is on top of
the distributor shaft.

Fig. 6 Cutaway ignition distributor and

vacuum-advance unit, with rotor and cap in
place.

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In most contact-point distributors, the
distributor shaft is driven from the engine
camshaft by a pair of spiral gears (Fig. 7).
The rotor has a metal blade. One end of
the blade contacts the center terminal of
the distributor cap (Fig. 5).

When the rotor turns, the other end

passes close to the outer terminals in the
distributor cap. These are connected by
spark-plug wires to the spark plugs. The
high-voltage surge jumps the small gap
from the rotor blade to the terminal. The
spark-plug wires carry the high-voltage
surge to the spark plug in the cylinder that
is ready to fire.

Fig. 7 Simplified secondary circuit, The coil

secondary winding is connected through
the distributor cap, rotor, and wiring to the
spark plugs.

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4. SECONDARY IGNITION CABLES The
second ignition cables or wiring include
the coil wire and the spark-plug wires.
These cables connect between the center
of the ignition coil and the distributor cap,
and between the distributor cap and the
spark plugs. Figure 8 compares the
construction of an older, spark-plug wire
with the resistance cable now used on all
cars. Secondary cables for contact-point
ignition systems have a 7mm (0.276 inch)
diameter. Many electronic ignition systems
require 8mm (0.315 inch) cables. The use
of a silicone insulating jacket makes these
cables larger.

Fig. 8 Silicone resistance cable or spark-

plug wire (left) now used on all vehicles
compared with older solid-conductor (right)
spark-plug wire, (AC-Delco Division of
General Motors Corporation)

5. SPARK PLUGS The spark plug has two

solid-metal conductors called electrodes
positioned to form a gap. The gap is
between the insulated center electrode
and the ground electrode. The spark
jumps the gap to ignite the compressed
air-fuel mixture in the engine cylinders.

Fig. 9 Spark plug electrodes.

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6. DISTRIBUTOR ASSEMBLY

a. Contact-Point Ignition
Distributor

The contact-point set mounts on

the breaker plate in the distributor
(Fig. 10). The points are operated
by a breaker cam on top of the
distributor shaft. The cam has the
same number of lobes as there are
cylinders in the engine. As the cam
revolves and the points close and
open, they act as a mechanical
switch to make and break the
primary circuit.

One contact point is mounted

on the grounded breaker plate and
is stationary. The other point
mounts on the end of an insulated
movable arm. The arm swings back
and forth on a pivot as the cam
lobes push on the rubbing block to
open the points. A spring attached
to the movable-point arm closes
the points.

When the points close, this

connects the coil primary winding
to the battery. A magnetic field
builds up in the coil. As the breaker
cam rotates, the next lobe pushes
the movable arm away from the Fig. 10. Top view of a contact-point ignition
stationary contact point. This distributor with the cap and rotor removed.
Note that the cam has six lobes (for a six
opens the points and stops the cylinder engine). The drawings at the top show
current flow. The magnetic field the cam action. When a lobe moves under the
collapses and a high-voltage surge rubbing block, the contact arm is moved,
results. The length of time in separating the points. (Delco-Remy Division of
degrees of distributor-shaft General Motors Corp).
rotation that the contact points
remained closed in the dwell.

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 The distance that separates the
points when they are fully open is
the gap. Points are normally
adjusted by dwell or gap
measurements.j

The distributor shaft and cam

are driven by the engine camshaft
which turns at one-half crankshaft
speed. It takes two complete
revolutions of the crankshaft to
rotate the distributor shaft one
complete revolution.

The relationship between piston position and spark plug firing is ignition
timing.

b. Electronic Ignition System

Contact-point and electronic ignition systems are similar, is operational

and also often in construction. Both distributors may have centrifugal and
vacuum-advance mechanisms. The major difference is the use of an
electronic switch instead of a mechanical switch (contact points) to control
the primary current. The electronic distributor has an armature or reluctor
and a magnetic sensor or pick-up coil instead of a breaker cam and contact
points. Like the breaker cam, the reluctor has the same number of teeth or
tips as there are cylinders in the engine. When the reluctor rotates, each
tooth creates a voltage pulse in the pickup coil. This signals the ignition
module to open the primary circuit.

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 Fig. 11. Components in an electronic-ignition using a pick-up coil distributor, with a
simplified electronic control module (ECM). The pick-up coil voltage signal is shown at the
lower right. (General Motors Corporation).

The ignition module may be a separate ignition unit or mounted on or in

the distributor. Engines with an electronic-engine-control system may not
have a separate ignition module. The engine controller or electronic control
module (ECM) completely controls the ignition system.

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c. High-Energy Ignition
(HEI) System

Many electronic ignition

systems produce higher secondary
voltage than contact-point
ignition. The voltage in these high-
energy ignition (HEI) systems can
reach 47,000 volts or higher. This
allows the use of spark plugs with
wider gaps. The longer spark can
ignite leaner air-fuel ratios. These
provide better fuel economy and
reduced exhaust emissions.

The secondary circuits are

basically the same in both ignition
systems, however, the distributor,
ignition coil, and secondary wiring
are redesigned to handle the
higher voltage. Distributor caps
are larger with the spark plug
terminals taller and farther apart.
This reduces the possibility of
arcing between terminals. Arcing
can cause engine miss and can
damage the cap. The capacitor
reduces radio interference (static). Fig. 12. Distributor, rotor and cap for a high-
HEI systems also use the larger 8- energy ignition (HEI) system. Note wider
mm silicone spark-plug wires and distributor and higher more widely spaced
terminals on the cap that reduces arcing
coil wire. Some General Motors HEI between terminals. (Delco-Remy Division of
systems for V-type engines mount General Motors Corporation)
the ignition coil on the top of the
distributor cap. This simplifies
ignition wiring. The HEI coil has a
different shape and produces a
higher voltage than the coil of
contact-point systems. However,
its basic operation is the same.

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 d. Distributor with Electronic Spark Advance

The electronic ignition systems describe above are usually on cars without
an electronic-engine control system. Cars with an electronic-engine-control
system and a distributor usually have electronic spark advance. Centrifugal
and vacuum-advance mechanisms are not used. The computer or ECM
controls spark advance based on inputs from various sensors.

Fig. 13. Electronic ignition with electronic spark advance (Ford Motor Company).

Electronic spark advance affects only the primary circuit of the ignition
system. There is no change in the secondary circuit.

Figure 13 shows an electronic ignition system using electronic spark

advance. The ignition module and the ECM work together to control spark
timing. The ignition module mounts on the distributor housing. Inside the
distributor, a profile ignition pick or PIP sensor signals the ignition module as
each piston nears top dead center (TDC). The ignition module shares this
information with the ECM which then computes spark advance. The ECM
produces a new signal that Ford calls the spark output (SPOUT) signal. It is
sent back to the ignition module, which opens the primary circuit at the
proper time to fire the spark plug.

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 Sometimes the ECM or other part fails in the electronic engine control
system. This may cause the engine to enter in limp-in or limited-operating
strategy (LOS) mode. Then the ignition module uses only the signal from the
sensor in the distributor to open and close the coil primary circuit.

PRIMARY RESISTANCE

Excessive current flow in the primary circuit causes arcing and burning of the
contact points. To prevent this, a resistance is placed between the ignition
switch and the coil primary winding. The resistance may be a separate
resistor or a special resistance wire. For easier starting, the resistance is
bypassed and full battery voltage reaches the coil during cranking. After the
engine starts, the resistance reduces coil voltage from 5 to 8 volts.

SECONDARY VOLTAGE

The high voltages and high

rate of charge prevent many
voltmeters from measuring
secondary voltage. Figure 9
shows a computerized engine
analyzer that includes two
cathode-ray tubes (CRTs).
The CRT is an oscilloscope or
scope. It can display the
primary and secondary
voltage patterns and the
length of time this occurs.

Figure 15 shows the basic

pattern for on spark plug
firing cycle in the secondary
circuit. On the left, the points
open. This stops the current
flow through the coil primary
winding. The magnetic field,
then collapses, causing a
sudden high voltage (A to B)
in the secondary winding.
Figure 14. Computerized Engine Analyzer.
This is the firing voltage that
starts the spark jumping the
gap on the spark plug. The
volt quickly drops from B to C
because it takes less voltage
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to sustain the spark than it
does to start it. The spark
continues from C to D, where
it stops.
This is the spark line burn
time. It lasts for about 20
degrees of crankshaft
rotation, or 1 to 2
milliseconds (thousands of a
second). The remaining
energy causes voltage ripples
or oscillations from D to E in
Fig. 15. However, the voltage
is not great enough to restart
the spark. At E, the points
close and current starts
flowing through the coil
primary winding. The Figure 15. Oscilloscope waveform or trace, showing
one complete spark-plug firing cycle in the secondary
expanding magnetic lines of circuit. The dwell section is the time period during
force pass through the which current flows through the primary circuit.
primary winding, creating a
slight alternating voltage in it.
This is shown by the dip and
small ripples to the right of E
in Fig. 15.

From E to F is the dwell

section.

Dwell is the length of time the points are closed and current flows through
the primary winding of the coil. Then at F, the points open and the cycle
begin again at A as the spark occurs at the spark plug. The whole procedure
repeats continuously as long as the engine runs.

ADVANCING THE SPARK

When the engine is idling, the spark is timed to reach the spark plug just
before the piston reaches TDC on the compression stroke. At higher speeds,
the spark must occur earlier. If it does not, the piston will be past TDC and
moving down on the power stroke before the combustion pressure reaches
its maximum. The piston is ahead of the pressure rise which results in a weak
power stroke. This wastes much of the energy in the fuel.

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To better use the energy in the fuel, the spark takes place earlier as engine
speed increases. This spark advance causes the mixture to burn producing
maximum pressure just as the piston moves through TDC. Most contact-point
distributors have two mechanisms to control spark advance. A centrifugal-
advance mechanism adjusts the spark based on the engine speed. A vacuum
advance mechanism adjusts the spark based on engine load. On the engine,
both work together to provide the proper spark advance for the engine
operating conditions.

CENTRIFUGAL ADVANCE

The centrifugal-advance
mechanism advances the
spark by pushing the
breaker cam ahead as the
engine speed increases.
Two advance weights, two
weight springs, and a cam
assembly provide this
action. The cam assembly
includes the breaker cam
and an oval-shaped
advance cam (Fig. 16). At
low speed, the springs hold
the weights in. As engine
speed increases, centrifugal
force causes the weights to
overcome the spring force
and pivot outward (Fig. 16).
This pushes the cam
assembly ahead. The
contact points open and
close earlier, advancing the
spark.

Figure 16. Parts of a centrifugal-advance mechanism for

a contact-point distributor.

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VACUUM ADVANCE

When the throttle valve is

only partly open, a partial
vacuum develops in the
intake manifold. Less air-
fuel mixture gets into the
engine cylinders. Then the
fuel burns slower after it is
ignited. The spark must be
advanced at part throttle to
give the mixture more time
to burn.

Figure 17. Centrifugal-advance mechanism in no-

advance and full-advance positions. In the example
shown, the ignition is timed at 8 degrees before TDC on
idle. There is no centrifugal advance at 1,000 engine
rpm. At 4,000 engine rpm, there is a total of 28 degrees
advance (8 degrees original timing plus 20 degrees
centrifugal advance).

The vacuum-advance
mechanism Fig. 16 and
18) advances spark
timing by shifting the
position of the breaker
plate. The vacuum-
advance passage
connects the diaphragm
to a port just above the
closed throttle valve.
When the throttle valve
moves past the vacuum Figure 18. When the throttle valve is closed, there is no
port, the intake manifold vacuum advance. The ported vacuum passage is above the
pulls on the diaphragm. closed throttle valve.
This rotates the breaker
plate so the contact
points open and close
Document No.
Date Developed:
Issued
Automotive Servicing June 2009
by:
NC II
Page 25 of 33
Developed by:
Servicing Ignition Glenn Joy A. Alipio
System
earlier (Fig. 18).

Any vacuum port above

the throttle valve
provides ported vacuum.

Figure 19. Operation of the vacuum-advance unit. When

the throttle valve moves past the port, intake-manifold
vacuum is admitted to the vacuum-advance unit on the
distributor. The breaker plate then rotates to advance the
spark.

COMBINED CENTRIFUGAL AND VACUUM ADVANCE

Document No.
Date Developed:
Issued
Automotive Servicing June 2009
by:
NC II
Page 26 of 33
Developed by:
Servicing Ignition Glenn Joy A. Alipio
System
At any speed above idle, there is
some centrifugal advance.
Depending on the intake-manifold
vacuum, there may also be some
vacuum advance. The total
advance curve in Fig. 20 shows
how the centrifugal and vacuum
advance combined. At 40 miles
per hour (64 km/h), there are 15
degrees of centrifugal advance.
The vacuum advance can
produce up to 15 degrees of
additional advance at part
throttle. The advances shown in
Fig. 20 combine to produce a
maximum advance of 30 (15 +
15) degrees.

When the engine runs at wide-

open throttle, intake manifold Figure 20. Centrifugal and vacuum advance
vacuum drops to zero. There is no curves for one engine.
vacuum advance. Normally, the
total advance varies between the
straight line (centrifugal advance)
and the curved line (centrifugal
plus vacuum advance) in Fig.20.

Document No.
Date Developed:
Issued
Automotive Servicing June 2009
by:
NC II
Page 27 of 33
Developed by:
Servicing Ignition Glenn Joy A. Alipio
System
SPARK PLUGS

The spark plug has a metal outer

shell enclosing a ceramic
insulator. Centered in the
insulator is the center electrode
which carries the high-voltage
current from the ignition coil. A
ground electrode attaches to the
metal shell and is bent inward to
produce the proper spark gap.
The gap varies from 0.035 inch
(0.9 mm) for contact-point
ignition systems to 0.080 inch
(2.03 mm) for some electronic
ignition systems. The spark jumps
from the center electrode to the
ground electrode. The wider the
gap, the higher the voltage
required to jump it. Figure 21. Cutaway resistor-type spark plug. The
center electrode is insulated. The side electrode
is grounded through the engine. (AC Spark Plug
Spark plugs may have a
Division of General Motors Corporation)
suppressor or resistance built into
the center electrode (Fig. 21). It
reduces television and radio
interference (static) caused by
the ignition system. Spark plugs
may require gaskets when
installed to assure a leak proof
seal. Many engines use spark
plugs with tapered seats, which
seal without a gasket. Some
spark-plug threads are coated
with an anti-seize compound. This
makes plugging removal easier,
especially from aluminum
cylinder heads.

Document No.
Date Developed:
Issued
Automotive Servicing June 2009
by:
NC II
Page 28 of 33
Developed by:
Servicing Ignition Glenn Joy A. Alipio
System
Some engines have two spark
plugs in each combustion
chamber. Both plugs may fire
together or one slightly ahead of
the other. The additional plugs
help reduce exhaust emissions
and increase engine power.

Most spark plugs have electrodes

made of nickel and chrome alloys
that resist corrosion. Some
ground and lower center Figure 22. Spark plugs with center electrodes that
have a (A) copper core and a (B) platinum tip.
electrodes have a copper core. (Robert Bosch Corporation)
Others also have a thin-wire
platinum tip. These foul and
misfires less often, last longer,
and have a greater heat range
than other plugs.

IGNITION SWITCH

The ignition switch does

several jobs. It turns the
ignition system on and off.
It has a START position for
operating the starting
motor. It operates the
steering-wheel lock, an
audible or light signal if the
ignition key is in the
ignition lock when a door
opens or if seat belts are
not buckled. On many
vehicles, the electric fuel
pump connects to the Figure 23. Combination ignition-switch and steering-
battery through the wheel lock, showing the opening mechanism inside the
ignition switch. Other steering column. (General Motors Corporation)
accessories such as radio
and heater blower motor
also receive current
through the ignition switch.

Document No.
Date Developed:
Issued
Automotive Servicing June 2009
by:
NC II
Page 29 of 33
Developed by:
Servicing Ignition Glenn Joy A. Alipio
System
In most cars, the ignition key is placed in the ignition lock, or lock cylinder in
the steering column (Fig. 19). The ignition switch may attach to the lock, or
go further down the steering column. Turning the ignition key moves an
actuator rod that operates the ignition switch.

The five positions of the ignition lock are ACCESSORY, LOCK, OFF, RUN, and START.
Figure 19 shows how the ignition lock operates the steering-wheel lock. The
notched disk is splined to the top end of the steering shaft. With the
automatic transmission in PARK, the driver turns the key to LOCK. The spring-
loaded plunger moves up into a notch in the disk, locking the steering wheel.
This also locks the transmission in park.

If the key will not move to LOCK,

turn the steering wheel until the
plunger and a notch align. Then
the spring will force the plunger
up and the key will turn to LOCK.
Turning the key from LOCK to OFF
pulls the plunger out of the Figure 24. Ignition-system oscilloscope pattern.
notch in the disk. This unlocks
the steering wheel and the
transmission.

Document No.
Date Developed:
Issued
Automotive Servicing June 2009
by:
NC II
Page 30 of 33
Developed by:
Servicing Ignition Glenn Joy A. Alipio
System
 JOBSHEET 9.1-1
Servicing Ignition System

Trainee Name: ________________________ Date: _________________

JOBSHEET 9.1-1

Title: Servicing Ignition System

Performance Objectives: Given the equipment and tools, perform
Servicing Ignition System based instruction from the Trainer.
Tools/Equipment:
 Engine mock-up
 Spark plug
 Contact point
 Ignition switch
 Battery
 Distributor
 Mock-up
 Ballast/resistor
 VOM
 Engine analyzer
Steps/Procedure:

1. Secure the Job sheet form from your Trainer.

2. Prepare the needed equipment and tools.
3. Role procedure on identifying parts and components of the
ignition system
4. The trainer gives feedback on the performance.

Assessment Method
Demonstration

Document No.
Date Developed:
Issued
Automotive Servicing June 2009
by:
NC II
Page 31 of 33
Developed by:
Servicing Ignition Glenn Joy A. Alipio
System
 Performance Criteria Checklist for
Job Sheet 9.1-1

Trainee’s Name ___________________________ Date_____________

Criteria YES NO
1. Ignition system components are identified

2. Functions of the ignition system are

understood

3. Standard clearance and resistance of ignition

system components are determined

4. The operating principle of the ignition

system is explained

Comments/Suggestions:

Trainer:__________________________ Date_____________

Document No.
Date Developed:
Issued
Automotive Servicing June 2009
by:
NC II
Page 32 of 33
Developed by:
Servicing Ignition Glenn Joy A. Alipio
System