Emissions

Question 1

What causes hydrocarbon emissions to be released from an engine’s exhaust?

Answer 1

Incomplete combustion or improper air-fuel mixture, often due to issues with injectors, ignition, or air induction.

Question 2

How are oxides of nitrogen (NOx) formed in the combustion chamber?

Answer 2

NOx is formed at high combustion temperatures, typically due to high compression or excessive engine load.

Question 3

What are the causes of increased exhaust emissions?

Answer 3

Faulty sensors, malfunctioning EGR systems, poor combustion, and issues with fuel injectors.

Question 4

How do oxygen emissions relate to air-fuel ratio?

Answer 4

A rich mixture (too much fuel) leads to HC emissions, while a lean mixture (too little fuel) causes increased NOx emissions.

Question 5

How does the evaporative control system operate during the purge and non-purge modes?

Answer 5

In purge mode, the system vents fuel vapors from the canister into the intake manifold. In non-purge mode, the vapors are stored in the canister.

Question 6

What is the function of the knock sensor and electronic spark control module?

Answer 6

The knock sensor detects detonation and sends a signal to the electronic spark control module to adjust ignition timing.

Question 7

What is the purpose of an EGR valve?

Answer 7

The EGR valve reduces NOx emissions by recirculating a portion of the exhaust gases back into the combustion chamber.

Question 8

What is the purpose of a catalytic converter?

Answer 8

It converts harmful emissions (CO, NOx, HC) into less harmful substances (CO2, N2, H2O) through chemical reactions.

Question 9

How does a secondary air injection system work?

Answer 9

It introduces additional air into the exhaust stream to help burn excess hydrocarbons and carbon monoxide.

Question 10

What are common emission controls found on light-duty diesel engines?

Answer 10

Diesel engines use EGR, selective catalytic reduction (SCR), and diesel particulate filters (DPF) to meet emission standards.

Question 11

How does the air induction system work?

Answer 11

It includes ducts, air cleaners/filters, and intake manifolds that supply clean air to the engine for combustion.

Question 12

What is the purpose of a turbocharger?

Answer 12

A turbocharger increases engine efficiency and power by compressing air entering the engine, improving air-fuel mixture.

Question 13

What are common problems with a turbocharger?

Answer 13

Turbo lag, excessive smoke, or lack of power, often due to issues with bearings, seals, or the compressor.

Question 14

How does a supercharger work?

Answer 14

A supercharger boosts engine power by forcing air into the intake. Common issues include noise, belt slippage, and overheating.

Question 15

What are the components of an exhaust system?

Answer 15

The exhaust system includes the manifold, gaskets, pipes, catalytic converters, mufflers, and resonators.

Question 16

What should be done during an exhaust system inspection?

Answer 16

Inspect for leaks, ensure all components are properly connected, and check for rust or damage to pipes, gaskets, or seals.

Question 17

How does a scan tool help in vehicle diagnostics?

Answer 17

A scan tool reads and clears diagnostic trouble codes (DTCs), monitors live data, and helps diagnose issues within the vehicle’s systems.

Question 18

What does OBD-II stand for?

Answer 18

On-Board Diagnostics, second generation. It’s a system that monitors vehicle emissions and engine performance.

Question 19

What is the purpose of a warm-up cycle in an OBD-II system?

Answer 19

The warm-up cycle helps the vehicle’s sensors and components to reach optimal operating conditions, enabling accurate diagnostics.

Question 20

What is a trip cycle in the context of OBD-II?

Answer 20

A trip cycle refers to the specific conditions under which the vehicle’s systems are monitored, such as driving patterns or engine temperature.

Question 21

Why are two oxygen sensors used in the exhaust system?

Answer 21

One sensor monitors the exhaust before the catalytic converter (upstream), while the second monitors it after the converter (downstream) to ensure the converter is functioning properly.

Question 22

What should be done if you suspect a malfunctioning fuel injection system?

Answer 22

Perform a no-start diagnosis, check fuel pressure, inspect injectors, and check for any leaks or blockages in the system.

Question 23

What is an injector balance test?

Answer 23

It tests the performance of each fuel injector by comparing fuel delivery and timing to ensure all injectors are working properly.

Question 24

How do you test a fuel injector with a noid light?

Answer 24

A noid light is plugged into the injector connector to check if the injector is receiving the proper electrical signal.

Question 25

How do you perform a pressure and volume output test on an electric fuel pump?

Answer 25

Attach a pressure gauge and measure the fuel pressure, then check the volume of fuel delivered to ensure it meets manufacturer specifications.

Question 26

What are common signs of an issue with a GDI system?

Answer 26

Issues with fuel delivery, clogged injectors, or poor combustion that leads to rough idle, misfires, or poor acceleration.

Question 27

How do you diagnose improper idle speed on fuel-injected vehicles?

Answer 27

Check for vacuum leaks, inspect the idle air control valve, test for fuel pressure, and verify that the throttle body is clean and functioning.

Question 28

What are the steps for servicing a fuel filter?

Answer 28

Inspect the fuel filter for clogging, remove and replace it if necessary, and ensure that the filter is properly mounted and sealed.

Question 29

What are the components of a fuel delivery system?

Answer 29

It includes the fuel tank, fuel pump, fuel filter, fuel lines, and injectors.

Question 30

How do you inspect and service fuel lines and tubing?

Answer 30

Check for leaks, cracks, or blockages in the fuel lines. Replace any damaged sections, and ensure all connections are tight.

Question 31

What are the different fuel filter designs and mountings?

Answer 31

Fuel filters can be inline, canister-style, or integrated with the fuel pump, typically mounted along the fuel line.

Question 32

How do you remove and replace a fuel filter?

Answer 32

Relieve fuel system pressure, disconnect the fuel lines, remove the old filter, and replace it with a new one, ensuring proper mounting and seal.

Question 33

How does an electric fuel pump circuit work?

Answer 33

The electric fuel pump is activated by the fuel pump relay, which sends power to the pump when the ignition is turned on, pumping fuel to the injectors.

Question 34

How do you conduct a pressure and volume output test on an electric fuel pump?

Answer 34

Attach a pressure gauge to the fuel line and measure the fuel pressure. Then, measure the fuel volume to ensure it meets manufacturer specifications.

Question 35

How do you service and test an electric fuel pump?

Answer 35

Inspect for power and ground at the pump, check fuel pressure output, and verify that the pump is delivering the correct fuel volume and pressure.

Question 36

What is the basic composition of gasoline?

Answer 36

Gasoline is primarily composed of hydrocarbons, with additives for engine performance, fuel stability, and emissions control.

Question 37

Why are materials added to gasoline to make it more efficient?

Answer 37

Additives such as detergents, antioxidants, and oxygenates improve combustion efficiency, reduce carbon deposits, and reduce emissions.

Question 38

What are common substances used as oxygenates in gasoline, and what do they do?

Answer 38

Oxygenates like ethanol and MTBE are added to gasoline to increase the oxygen content, promoting cleaner combustion and reducing emissions.

Question 39

How is the quality of a fuel tested?

Answer 39

Fuel quality can be tested by measuring its octane rating, checking for contaminants, and performing tests on volatility, density, and sulfur content.

Question 40

What are the advantages and disadvantages of various alternative fuels?

Answer 40

Alternative fuels like ethanol, propane, and natural gas offer cleaner emissions but may have limitations in energy density, availability, or cost.

Question 41

What is the difference between diesel fuel and gasoline?

Answer 41

Diesel fuel has a higher energy density, is less volatile, and has different combustion characteristics compared to gasoline. Diesel engines use compression ignition, while gasoline engines use spark ignition.

Question 42

What are common types of fuel injection used on diesel engines?

Answer 42

Diesel engines typically use direct injection (DI) or common rail direct injection (CRDI), which injects fuel directly into the combustion chamber under high pressure.

Question 43

What techniques are used to allow current diesel engines to meet emission standards?

Answer 43

Techniques include exhaust gas recirculation (EGR), selective catalytic reduction (SCR), and diesel particulate filters (DPF) to reduce NOx and particulate emissions.

Question 44

What steps should you take to perform a no-start diagnosis?

Answer 44

Check for fuel, spark, and air supply, inspect the ignition system, fuel system, and compression, and use diagnostic tools like a scan tool or multimeter.

Question 45

How do you determine the cause of an engine misfire?

Answer 45

Check for fuel, ignition, and air issues, perform a compression test, and inspect components like spark plugs, injectors, and ignition coils.

Question 46

How do you test ignition system components using a voltmeter, ohmmeter, and test light?

Answer 46

A voltmeter measures voltage, an ohmmeter checks resistance, and a test light confirms the presence of voltage or current at components like the ignition coil or spark plugs.

Question 47

How do you perform a visual inspection of ignition system components?

Answer 47

Inspect spark plugs, ignition wires, coils, and connections for wear, damage, or corrosion that could lead to misfires or ignition issues.

Question 48

What is the effect of incorrect ignition timing?

Answer 48

Incorrect ignition timing can cause engine misfires, poor performance, knocking, or excessive exhaust emissions.

Question 49

How do you check and set ignition timing?

Answer 49

Use a timing light to check the timing marks on the crankshaft pulley and adjust the timing as needed using the distributor or timing control module.

Question 50

How do you diagnose engine misfiring on electronic ignition-equipped engines?

Answer 50

Check for spark at each cylinder, inspect injectors and sensors, test the ignition system, and ensure the correct air-fuel mixture.

Question 51

What are the three basic types of ignition systems?

Answer 51

The three basic types are conventional ignition systems (points and condenser), transistorized ignition systems, and electronic ignition systems.

Question 52

What are the two major electrical circuits used in all ignition systems?

Answer 52

The primary circuit (from the battery to the coil) and the secondary circuit (from the coil to the spark plugs).

Question 53

How do ignition coils, spark plugs, and ignition cables operate?

Answer 53

The ignition coil transforms low voltage into high voltage, which is sent through ignition cables to spark plugs, where it ignites the air-fuel mixture.

Question 54

How is high voltage induced in the coil secondary winding?

Answer 54

When current in the primary winding is interrupted, the collapsing magnetic field induces a high voltage in the secondary winding, which is then sent to the spark plugs.

Question 55

What are the various types of spark timing systems, including electronic switching systems?

Answer 55

Types include mechanical, vacuum advance, and electronic timing systems, with modern systems using sensors to detect engine position and adjust timing.

Question 56

How does a distributorless ignition system work?

Answer 56

A distributorless ignition system uses multiple coils for each cylinder and an engine control module (ECM) to control spark timing without the need for a traditional distributor.