P O C K E T
G U I D E
Ignition
Coils
Never settle for second best, always insist
on NGK.
First it was Spark Plugs.
Next came Glow Plugs.
Then Lambda Sensors.
Now Ignition Coils from the
name you know and trust.
NGK.
Quick guide to
Ignition Coil technology
The operating principle is essentially the same for all types – whether the
classic can-type coil, or in a coil rail system. The device contains two copper
wire windings and a laminated iron core. The copper wires are insulated to
prevent short circuits. The battery current fed through the primary winding
produces a magnetic field whose strength is further increased by the iron
core. When this circuit is opened, the magnetic field collapses, inducing a
high voltage pulse in the secondary coil. This pulse is fed through the H.T.
connection to the spark plugs. As an integral part of the ignition system,
the coil produces the high voltage required to produce the electric spark to
ignite the fuel. The relatively low battery voltage, around 12 V, is
transformed to up to 45,000 V.
NGK Ignition Coil types
Can-type ignition coils
In older vehicles and vintage cars, you might
still find what is commonly known as a can-type
ignition coil. These types are traditionally filled
with oil for insulating, cooling and protection
against moisture.
Distributor coils
For this type, the induced high voltage reaches the
individual spark plugs via a mechanically driven distributor
mechanism. These are an evolution of the can-type coil and
were widely used until the 1990s.
Ignition blocks
Ignition blocks contain several ignition coils, which are
connected by H.T. cables to each plug. This ignition coil
type is available with single or dual spark technology. In
single-spark ignition blocks, each ignition cable supplies
the high voltage pulse to one cylinder. In dual-spark blocks,
the high voltage pulse is fed simultaneously to two cylinders,
one that is on the power stroke the other being on the
exhaust stroke and thus has a “wasted spark”.
NGK Ignition Coil types
Pencil or coil on plug ignition coils
This ignition coil type is mounted directly on top
of the spark plug. The high voltage pulse is fed
straight to the spark plug, minimising power
loss. As pencil ignition coils are mounted in the
spark plug tunnel, they do not take up space in
the engine compartment. Pencil ignition coils
are used in vehicles with electronic ignition
systems and are available as single-spark or dualspark coils.
Ignition coil pack systems
So called coil packs combine a number of pencil ignition
coils mounted within a single component known as a rail.
This rail is then placed across a bank of several spark plugs.
The facts about
Ignition Coils and service
intervals
As with most components, ignition coils are
subject to wear and tear. There are however
many factors that might reduce their service
life. Before replacing an ignition coil, it’s
worth checking whether any of the problems
on the following pages could have caused the
fault.
Internal short circuits causing overheating
It is a well-known fact that the risk of overheating due
to internal short circuits increases with the age of the
ignition coil. Sustained temperatures over 150°C can cause
irreparable damage to the coil. However, in many cases,
overheating is caused by a fault in the ignition module of
the engine control system.
Fault in power supply
Defective ignition cables and low battery power can lead
to insufficient voltage supply and thus prolonged charging
times of the ignition coil. This can damage the ignition
module and eventually lead to coil failure.
The facts Continued
Mechanical Damage
Ignition components have also been known to be damaged
by rodents! Other mechanical damage includes degradation
of the insulation by abrasion or contamination caused by oil
leaks.
Thermal Problems
Pencil ignition coils installed in the spark plug tunnels of
the engine are exposed to extremely high temperatures,
which can shorten the service life of the coils.
ged
ion
by oil
of
Faulty Contacts
If the ignition coil housing is damaged, moisture can
penetrate the primary and secondary coil area resulting in
internal resistance problems. Such faults can be caused by
something as simple as leaking windscreen washer nozzles
or during heavy rain. Road salt is also known to cause
contact faults due to corrosion.
Vibration
As some coil types are mounted directly onto the engine
they can suffer from damage by prolonged excessive
combustion vibration.
Troubleshooting
Ignition Coil problems
If the vehicle fails to start, the engine misfires or the car’s acceleration becomes increasingly
poor, the ignition coil might be defective. Here are some basic checks that should be carried
out to establish where the fault might lie.
1. Visual inspection
Error codes that indicate an ignition fault might be caused by the actual coils or by another system
problem. Before checking the ignition coil, you should firstly inspect the ignition system for signs of
damage.
> Is there any mechanical damage? > Do you detect hairline cracks?
> Is there any damage to the electric cables and plugs? > Are components corroded or kinked?
> Is there sufficient battery power to the ignition system? > Are there any signs of oil or water
contamination?
2. Resistance measurement with ohmmeter
Many conventional coils for use with contact breakers, transistorised and electronic ignition systems with
map-controlled ignition can be tested whilst in situ by measuring the electrical resistance of the primary
and the secondary circuit. Great care should be taken when carrying out these tests to prevent
damage to circuits and on some designs it is not possible to make effective measurements due to the
specific electrical architecture of the coil.
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U 1 000
Distributor coils
Coil Types
Ignition coil for vehicles with
mechanical ignition distributor.
One ignition coil powers several
spark plugs through a distributor.
The number of ignition cables
corresponds to the number of
spark plugs. An additional cable
is required to feed the voltage to
the distributor.
U 2 000
Ignition blocks
Ignition blocks – one or more block
per vehicle, depending on engine type.
One ignition block supplies several
spark plugs. Normally, one ignition coil
is required for each cylinder head.
The number of ignition cables
corresponds to the number
of spark plugs.
Coil Types
U 3 000
Ignition blocks with two
high-voltage terminals
One or more ignition blocks,
depending on application.
One ignition coil simultaneously
supplies two spark plugs.
U 4 000
Plug top coil with
double spark technology
Single pencil or COP-type ignition
coil supplies two spark plugs.
The ignition coil supplies two spark
plugs. The coil is mounted directly
on the first spark plug.
One ignition cable is needed
per coil.
The number of ignition cables
corresponds to the number of
spark plugs.
two
als
Coil Types
U 5 000
Plug top coil with
single-spark technology
Single pencil or COP-type
ignition coil per spark plug.
Each cylinder is equipped with a
single ignition coil.
There is no need for ignition
cables.
U 6 000
Ignition coil systems
Individual cylinder ignition coils
in complete rail system.
Compact ignition coil pack system
that supplies multiple spark plugs.
There are normally no ignition
cables required.
NGK Spark Plugs (UK) Ltd
Maylands Avenue
Hemel Hempstead
Herts
HP2 4SD
Tel: 01442 281000
Fax: 01442 281001
www.ngkntk.co.uk