Page 260 - Mechanic Diesel - TT

MECHANIC DIESEL - CITS

5 Key stuck in ignition

The key can get stuck due to the worn-out ignition cylinder or steering lock. Both of these causes will prevent the
key from rotating inside the switch.
Inspecting and elimating of common faults of engine ignition system

Under normal circumstances, the engine suddenly turns off during operation, and the reason for the failure to start
is mostly the failure of the ignition system. Ignition system failures are manifested as no fire, misfire, weak spark,
and incorrect ignition.
1 The engine cannot be started
Turn on the ignition switch and the engine cannot start. It may be caused by abnormal power supply, incorrect
ignition timing or poor spark plug.
• The spark is strong, indicating that the low-voltage circuit and the ignition coil are in good condition, and the
fault lies in the distributor and the high-voltage circuit of the spark plug.

• Weak or no sparks indicate that the low-voltage circuit and short circuit, open circuit, failure of ignition electronic
components or failure of ignition coil and central high-voltage line.
2 Energy requirements for ignition
The total enthalpy required to cause the flame to be self-sustaining and promote ignition, is given by the product
of the surface area of the spherical flame and the enthalpy per unit area. It is reasonable to assume that the basic
requirement of the ignition system is that it should supply this energy within a small volume. Further, ignition
should occur in a time interval sufficiently short to ensure that only a negligible amount of energy is lost other than
to establish the flame. In view of this last mentioned condition, it is apparent that the rate of supply of energy is
as important a factor as the total energy supplied. A small electric spark of short duration would appear to meet
most of the requirements for ignition. A spark can be caused by applying a sufficiently high voltage between two
electrodes separated by a gap, and there is a critical voltage below which no sparking occurs.
Magneto ignition system
The main disadvantage of the high tension magneto ignition system lies in the fact that the wirings carry a very
high voltage and thus there is a strong possibility of causing engine misfire due to leakage.
Battery ignition system
1 Battery is necessary. Difficult to start the engine when battery is discharged.
2 Maintenance problems are more due to battery.

3 Current for primary circuit is obtained from the battery. A good spark is available at the spark plug even at low
speed. Efficiency of the system decreases with the reduction in spark intensity as engine speed rises.
4 Occupies more space.
In today’s low emission and high-efficiency engines, the key to effective combustion is a consistent, high-energy
ignition output.
The high voltage required for ignition is provided by the Ignition Coil – a type of transformer that features primary
and secondary coils of wire wrapped in layers around an iron core.
The role of the Ignition Coil is to transform the low voltage in a car’s battery into the thousands of volts which
are used by the Spark Plug to generate sparking. These sparks ignite the air-fuel mixture inside the combustion
chamber.
Ignition Coils can sometimes fail before their usual service life due to wear and defects. These could include
overheating caused by internal short circuits, vibration, low battery power, defective ignition cables and mechanical
damage, to name a few.
There are many signs that there is a fault with the Ignition Coil, including:

• No combustion: No combustion occurs because no spark is emitted.
• Stalling: The engine stalls but can be restarted.
• Poor drivability: Hesitation during acceleration or the engine misfires.

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CITS : Automotive - Mechanic Diesel - Lesson 76 - 79