Light Vehicle Mechanical Technology

Questions

1

What is the function of an ignition switch?

The ignition switch is a master switch which provide the power for the vehicles electrical accessories, computer, fuel and ignition system.  The ignition system provides high intensity sparks at the spark plugs to ignite the fuel charges in the combustion chambers.

2

What is the function of the secondary circuit?

The secondary circuit produces the high voltage and distributes it to the spark plugs.

3

What is an ignition coil? What does it do?

Ignition coil operate on the principle of electromagnetic induction. It is a induction coil in ignition system which transforms the battery’s voltage to the different volts to create an electric spark in the spark plugs to ignite the fuel.

4

What is ‘Dwell’? What does this term refer to?

Dwell is the period of the time that the current flows in the primary circuit and a magnetic field dwells around the ignition coil. During this time the magnetic field in the coil is building maximum strength. If the dwell period is too short the field will not build sufficiently to generate a good spark.

5

How much secondary coil voltage is typically required to jump the spark plug gap?

20,000 to 50,000 volts

6

What is the purpose of the Capacitive Discharge (CD) system?

The capacitive discharge system is an electronic ignition device that stores an electrical charge and then discharge it through an ignition coil in order to produce a power spark from the spark plugs in a petrol engine. It is absorbs the voltage induced into the primary winding through self-induction.

7

Why is Copper used in the construction of electrodes?

Because copper has a better EDM wear resistance

8

What function do spark plug cables / ignition cables do?

A spark plug cables, and ignition cables carry high voltage current. They are heavily insulated. They transfer the spark from the distributor or ignition coil to the plugs.

9

Why would you not use a conventional 12V test light to diagnose components and wires in electrical systems?

Because 12V test light is only to check circuits and components while electrical current is flowing through them

10

What is an ohmmeter? How would you use one?

An ohmmeter is an electronic device that measures resistance in an electronic component or circuit. It works by using 2 probes to send a current through the circuit and measuring how much resistance in ohm that current encounter.

11

List 3 examples of protective personal equipment (PPE)

Safety glasses

Safety shoes

Safety gloves

12

How would you assess fuses during an ignition test? What would you check for?

By pulling the fuse from the starter and holding it up to the light to check if its metal strip is burned, broken or damaged. A broken or burned strip means that the fuse must be replaced

13

Explain how you would check a switch during ignition testing

First, insert the ignition key into the ignition switch and try to crank or start the engine. If the engine cranks, then the switch is in good working condition. If the engine fails to crank and a “click” is heard instead when the k;ey is turned to “III” position, then the problem is not with the ignition switch. However, if the engine fails to crank and neither a “click” is heard when the key is turned to “III” position, then the switch is damaged and should be replaced. 

14

When replacing a camshaft or crankshaft sensor, what is the significance of the air gap between the sensor and the trigger wheel?

The air gap between the sensor and the trigger wheel serves to prevent the loss of the timing signals from the crankshaft position sensors as well as prevent the engine from becoming cranky. 

15

How does planning your tasks before undertaking them assist workflow?

It ensures that tasks are assigned priority, thus accomplished in the order of their importance or effect on subsequent tasks.

16

What is a Kettering ignition system?

A type of inductive discharge system consisting of a battery, capacitor, ignition coil, ignition distributor and spark plugs. The system is used to convert the 12 V from a car battery into more than 20,000 V required to ignite the spark plug.   

17

What is a Magneto?

An electrical generator that produces periodic pulses of alternating current using permanent magnets.

18

What demands do vehicles place on ignition systems?

The need for precise timing and high voltage requirement during fuel ignition and initial combustion process. 

19

Why should you never unplug anything while the engine is running?

Because the different systems and components work in unison to maintain the combustion process and keep the engine running.

20

How would you remove a distributor?

First, check the high-tension leads that are connected to the cylinder then remove the distributor cap along with its HT leads. Thereafter, with the low-tension lead and the vacuum disconnected, remove the pinch-bolt by loosening the bolts used to attach the clamp plate to the engine, and remove the distributor carefully.  

21

How would you replace the igniter?

First, disconnect the car battery to avoid potential shock during the replacement. Afterwards, remove the engine cover and note down other components removed such as support horses and air filters. Then remove the cap and rotor from the distributor before finally removing the ignition ignitor. Check and verify that the ignitor is damaged and install a new ignitor by first grounding it and then sliding the male connectors into female connection slot. Lastly, reassemble the distributor and the battery, scan for errors and test drive the car. 

22

What is ignition timing and what does it do?

Ignition timing is the timing of the release of a spark, relative to the position of the piston and the crankshaft angle, in the combustion chamber close to the end of the compression stroke. It is used to control or calculate the time when the spark plug ignites during the compression stroke. 

23

List 3 sections generally included in a service and repair manual

Basic car safety

Fluids and oils

Tyres maintenance

Lights maintenance

24

What information can be found in a service and repair manual?

Information about the maintenance and troubleshooting of a vehicle’s basic components such as lights, tyres, safety belts and fluids

25

Where could you find an electronic version of a service / repair manual?

Can be downloaded in pdf formats from e-retailing platforms such as eBay.

26

How could you determine if a no-start condition is caused by the ignition system?

By performing a spark intensity check at one of the spark plugs using a test spark plug. If the test spark fails to fire on any of the plugs, then the no-start condition is caused by the ignition system ( Erjavec & Thompson, 2014).

27

What is the purpose of the battery in the ignition system?

To supply electrical energy of 12 volts to the ignition coil where the voltage is stepped up to levels high enough to produce a spark at the spark plug

28

A CarFix workshop owner agreed to allow a service person from Tipple Industries to conduct an assessment of, and service to, 3 hydraulic hoists. The hoists were in constant use, elevating vehicles for mechanical repairs and maintenance, in the mechanics workshop. This was a commercial business serving the general public. There were 4 employees working in the workshop.

None of the hoists had been serviced in the last 4 years. The minimum industry requirement is that they should be serviced yearly.

The service person from Tipple, who was an experienced hydraulic technician, duly conducted the assessments and was able to fully service two of the hoists. However, when he assessed the third hoist, the braking system, some of the cables and various other components were so worn and damaged that the technician felt the machinery was extremely unsafe and could not be serviced without extensive repairs. The workshop owner refused to contemplate paying for extra repair work. The technician's assessment, however, had led him to believe that unless repairs were instigated immediately the hoist would be a danger to the employees who used it. He discussed this with the employees who said that their employer would not care - that he would disregard safety requirements and make them use the hoist. They asked the technician if there was anything he could do.

Regardless of the requests from the employees the technician felt that he had no choice but to lock out the hoist and place the appropriate signage on the equipment. At this the workshop owner became angry and abusive and stated that he would remove the lockout tags and continue using the equipment. He rang the manager of Tipple Industries and complained that the service technician had acted improperly. He cut off the lock-out tags and insisted his employees continue using the hoist.

A few days later, while a car was on the damaged hoist, the braking cables failed completely. The front end of the hoist tilted and the customer's car fell, damaging the car, the workshop, other machinery and injuring two workers. Injuries to the workers were relatively minor - abrasions, bruises, cuts, a broken finger and a torn shoulder muscle; however, this was more due to luck than anything else.

28A

What are the duty of care components applicable to this case?

The duty of care components applicable to the case include cause in effect, proximate cause and harm/damage. Regarding cause in effect, the employees got injuries because their employer failed to repair the hoist and maintain it in safe conditions, which was part of his duty of care. Similarly, proximate cause is applicable to the case because they were the decisions and actions of the employer to remove the lock-out tags that led to the accident, thereby injuring the employees. 

28B

Is there a duty of care breach evident here?  If yes, by whom (explain your judgement)

 Yes, duty of care bridge is evident in the case. The breach of duty of care manifested when the owner refused to comply with the technician’s recommendations to have the hoist changes immediately due to the danger it posed both to the employees, customers, and even the workshop’s property. The owner seemed to care less about the workers’ safety and condition of the equipment, and even went ahead and removed the lock-off tags that the technician had placed on the hoist, and insisted that the equipment was safe for use. Evidently, this shows a high level of negligence by the workshop owner.

28C

What are the likely repercussions of this incident, under Workplace Health & Safety legislation and in regard to worker and customer reactions?

The workshop owner might be fined by the state court for violating the Workplace Health and Safety requirements that hydraulic hoists must be serviced annually.

The owner risks even more fines, and thus losses should the injured workers raise a lawsuit against him for negligence.

The injured workers and their colleagues might quit, which may cause the workshop to incur more losses as it might take long to find other experienced workers.

The customer whose car was damaged is more likely to discourage other potential customers from seeking repair services at the workshop

28D

Was this a foreseeable accident?  Explain your answer

The accident was foreseeable because there were many warming signs and missed opportunities such as the damaged cables and components that required extreme repairs to make them safe for operation.

28E

What should or could have been done to prevent this accident?

The workshop owner should have heeded to the technician’s advice and acted responsibly to approve and pay for extra repairs.

29

Why do organisations have Workplace Health and Safety policies and procedures?

The primary reason is to protect workers and equipment in the organization from both foreseen and unanticipated risks. This is because it enables the organization to regularly assess workplace safety and address potential hazards.

Having Health and safety procedures also enables organizations to comply with legal requirements and avoid financial losses associated with accident. 

30

What is the Workplace Health and Safety Act that relates to the state or territory you are being assessed in?

The Management of Health and Safety at Work Regulation

The Personal Protective Equipment at Work Regulations

31

How does a distributor work?

A distributor works by transferring voltage or electrical charges from the ignition coil to the spark plugs in each of the engine’s cylinders. A distributor typically includes a rotor and cap as the major components, and is driven by the car’s camshaft. The ignition coil, located outside the distributor and connected to the rotor via a spring-loaded carbon brush, produces very high voltages needed for entire process of ignition or staring the combustion. A rotor inside the distributor spins in synch with the engine’s camshaft, and this allows for transfer of the high voltage to the right spark plug in the engine’s cylinders. As the rotor spins, it creates a very small gap between it and the contacts, thereby allowing the high voltage from the rotor to pass through the gap to the contacts then to the engine’s wires and plugs.  

32

How do newer cars function without a distributor?

The cars have multiple ignition coils with each coil dedicated to delivering high voltage to one or two spark plugs. The overall ignition system and process is controlled by the Engine Control Unit (ECU). 

33

How does a waste spark ignition system work

The Wasted Spark Ignition system comprises of two spark plugs attached to the ends of coils (one coil for a two-cylinder engine, and two coils for a four-cylinder engine). During operation, the spark plugs fire simultaneously, with one plug firing in the compression stroke of one cylinder and the other plug fires in the exhaust stroke of the other cylinder. The extra spark fire in the exhaust stroke has no effect on ignition, and hence is considered to be “wasted”. The fact that the plugs are fired concurrently from the ends of one coil implies that their currents flow in opposite directions. In other words, the spark in one plug flows from the centre to the outside electrode, whereas the spark in the other plug flows to the centre from the outside electrode. 

34

What is the ignition coil?

An induction coil in a vehicle’s ignition system used to convert 12 volts from the vehicle’s battery to tens of thousands of volts required to create electric spark and jump it across the spark plug gap to ignite the engine's fuel.

35

What are the component differences between a step-up and step down coil?

 As step up coil has more windings on the secondary side than on the primary side to increase output voltage relative to the input voltage, whereas a step-down coil has lesser wraps or windings on the secondary side than on the primary side to reduce output voltages to suitable levels. As such, step up coils are used to supply voltage or power to such high voltage components as ignitors, while step down coils supply low power components such as sensors, rear cameras, USB devices and music players in the vehicle. 

36

Explain how you would adjust the ignition timing

With the engine at normal operating temperature and all the electrical loads turned off, detach the vacuum hoses and plug the hose. Next, disconnect the blind cap from the air adjusting screw and set the idle speed, then install the blind cap and remove the jumper wire off the test connector. Thereafter, attach a timing light to the vehicle’s engine and check if the initial ignition timing is 12^o11^o BTDC. If the timing is higher or lower that this specification, then looses the installation bolt on the distributor so that the distributor can easily rotate. Here, the ignition timing can be easily adjusted by turning or rotating the distributor.     

37

Why is ignition timing important?

It reduces excessive vibrations and allows the engine to produce the most usable force from the injected fuel, thereby improving the engine’s efficiency, power and longevity.

38

List 3 factors which influence ignition timing

 Engine compression ratio

Engine’s intake pressure

Fuel’s octane rating

Condition and efficiency of spark plugs

39

Explain how an electric ignition system controls timing advance

The manner in which electronic ignition system controls timing advance depends on the era or time that it was designed. Older electronic ignition systems control timing by utilizing either the centrifugal or vacuum advance. In those systems that use vacuum advance, timing advance is achieved by turning a movable plate against the rotation of the distributor shaft. On the other hand, more modern electronic ignition systems use on-board computers to retard or advance timing depending on the engine’s needs and current conditions such as temperature, system voltage, rate of air flow and throttle opening among other factors. The on-board computers on other ignition systems are equipped with ignition modules that directly controls the ignition coils.  

40

Why is knowing the firing order important when changing spark plug cables

To ensure that rewiring of the spark plugs matches the engine’s wiring configuration. This is because the firing order in a spark ignition engine is determined by the order in which the spark plugs are operated.  

41

How does magnetic induction work in ignition systems?

Magnetic induction, which depends on magneto technology, ignites the spark plug needed to fire the engine by generating high voltages. During operation, the magneto spins closer to a coil, creating a strong magnetic field that induces current in the secondary coil. As soon as the contact points or breaker open, the magnetic force collapses rapidly, thereby generating a high electric voltage in the secondary coil. This resulting high voltage ignites the spark plug, which consequently fires the engine.   

42

What is Hall Effect?

A phenomenon where a voltage difference produced across an electrical conductor is perpendicular both to the current flowing through the conductor and the applied magnetic field transverse to the current. The voltage difference is known as the Hall voltage.

43

What do the following spike patterns mean when testing ignition systems?

higher spikes

Shows high resistance that needs higher voltage to move the spark across the plug gaps. The condition could result from widened spark plug gaps due to wear and tear as well as from increased rotor air gap. 

lower spikes

The condition may indicate that the plug lead is low-resistance or shorted. It can also result from cross firing within the distributor or shorted spark plug in the engine cylinder.   

44

What do the following patterns mean when reading raster pattern systems?

Steep slope

Suggests that a valve in one of cylinders might be worn out, thereby causing uneven mixing of air and fuel.

Slope that starts at top of firing line

Indicates high resistance between the plug and the distributor cap as a result of corrosion in either the terminals of cables or the cap. 

Upwards slope

Indicates that the intake valves are either sticky, floating or burnt.