Union Test Prep Auto and Shop Information Part 2

What is a firing order?

the sequence in which the cylinders in an internal combustion engine ignite the air-fuel mixture to generate power.

What does the cylinder firing order impact?

It impacts the engine balance, smoothness, vibration, and overall performance.

Prope firing order helps….

distribute the load evenly across the engine components and ensures efficient power delivery.

How is the firing order determined?

It is determined by teh arrangement of cylindes itn e engine and teh crankshaft design.

What is the common firign order for inline-4 engines?

1-3-4-2

What is the typical firing order for an inline-6 engine?

1-5-3-6-2-4

What is the common firing order for V6 engines?

1-2-3-4-5-6 or 1-4-2-5-3-6, depiending on teh speicifc engine design.

What is the popular firing orders for V8 engines?

1-8-4-3-6-5-7-2 and 1-3-7-2-6-5-4-8

A disel engien is also refered to as….

A compression-ignition (CI) engine

Wat is a diesel engine?

a type of internal combustion engine that uses diesel fuel for power generation.

How does diesel engine ignte the fuel?

diesel engines use the heat generated from compressing air in the cylinder to ignite the fuel.

What is heat of compression?

the heat generated in the cylinder when the air is compressed during the compression stroke.

At what stage does air inside a piston become ighly compressed that it casues the temerpature to increase? is it when th piston moves up the cuylinder or down?

When tehpiston moves up in teh cylinder

What does a n intenal ecombustion engine need in order to operate efficiently?

It needs air-fuel mixture, ignition timing, and combustion. The three componenst are closly related, therefore an imbalance in one aspect will affect the engine’s overall performance and emissions.

What is an air-fuel mixture?

the combination of air and fuel that enters the engine cylinder and is burned during combustion.

Why is fuel needed in the air-fuel mixture?

Fuel contains the chemical energy that is released during combustion to create power.

Why is air needed in the air-fuel mixture?

Air provides oxygen, which allows the fuel to burn during combustion.

What is the air-fuel ratio, and why is it important?

The air-fuel ratio is the amount of air compared to fuel in the mixture.
The correct ratio affects engine performance, efficiency, and emissions.

What is the stoichiometric ratio?

the ideal air-fuel ratio where fuel burns completely with no excses oxygen or fuel remaining.

What is the stoichiometric ratio for gasoline engines?

A gasoline engine's ideal ratio is about 14.7 parts air to 1 part fuel (14.7:1).

Why is fuel atomized in an engine?

Fuel is broken into tiny droplets so it can mix better with air and burn more efficiently.

What is a lean air-fuel mixture?

A lean mixture has more air and less fuel than the ideal (stoichiometric) ratio.

What is one advantage of a lean mixture?

A lean mixture can improve fuel efficiency because it uses less fuel.

What problems can a lean mixture cause?

They can cause higher combustion temperatures, resulting in engine nknowcking, reduced power output, and potential engine damage.

What is a rich air-fuel mixture?

A rich mixture has more fuel and less air than the ideal (stoichiometric) ratio.

What is one advantage of a rich mixture?

A rich mixture can provide more power, especially during situations like acceleration.

What problems can a rich mixture cause?

Too much fule leads ti increased emiissions, reduced fuel efficency, and fouling of spark plugs or catalytic converters.

What is ignition timing?

the precise moment when the air-fuel mixture in the cylinder is ignited to initiate the combustion process.

How is ignition achived in gasoline engines?

Ignition occurs by a spark from the spark plug

Hpw is ignition achive in diesel engines?

Ignition occurs due to the heat of compression

Why is proper ignition timing important?

Proper timing allows the fuel to burn at the right moment, producing the most power and efficiency.

What happens if ignition timing is too early or too late?

Incorrect timing can cause:

• Reduced power

• Higher fuel consumption

• Increased emissions

How is ignition timing measured?

measured in degrees of crankshaft rotation

What does BTDC (Before Top Dead Center) mean?

the spark ignites the air-fuel mixture before the piston reaches the top of its compression stroke.

What does ATDC (After Top Dead Center) mean?

the spark ignites the air-fuel mixture after the piston has passed the top of its compression stroke and starts moving downward.

What is combustion?

A chemcial reaction between fuel and oxygen that releases energy in teh form of heat and pressure.

Where does combustion occur in an internal combustion engine?

Combustion occurs inside the engine's cylinders, where the air-fuel mixture burns.

How does combustion power a vehicle?

Combustion converts chemical energy in fuel into mechanical energy, which moves the engine and vehicle.

What is pre-ignition?

Pre-ignition occurs when the air-fuel mixture ignites too early, before the spark plug fires or before fuel is injected in a diesel engine.

What problems can pre-ignition cause?

• High cylinder pressure

• High temperatures

• Reduced engine performance

• Engine damage

What is detonation?

an uncontrolled and violent combustion event where the air-fuel mixture ignites on its own due to high pressure and temperature.

What is another name for detonation, and what does it sound like?

also called engine knocking or pinging and creates a knocking sound from pressure waves inside the cylinder.

What are the two types of engine cooling systems?

• Air-cooled → uses air to remove heat

• Liquid-cooled → uses coolant (most modern cars)

What does the coolant system do?

The coolant system curcilates a mixture of water and antifreeze (coolant) throug the engine to absorb and remove heat from the engine to prevent overheating.

What is coolant made of?

Water + Antifreeze

How does a liquid cooling system work?

• Coolant flows through the engine and absorbs heat.

• The coolant moves to the radiator.

• The radiator releases the heat into the air.

What does the water pump do in a cooling system?

circulates coolant through the engine and radiator.

What does the radiator do?

removes heat from the coolant by transferring heat into the air.

What does the radiator cap do?

controls the pressure inside the cooling system.

What do radiator hoses do?

transport coolant between the engine and radiator.

What does the thermostat do?

regulates engine temperature by opening and closing coolant flow to the radiator.

What is the purpose of the water jacket?

surrounds the engine cylinders and carries heat away from them.

What does the coolant recovery bottle do?

stores extra coolant as it expands when hot and contracts when cool.

What does the bypass tube do?

allows coolant to keep flowing through the engine when the thermostat is closed.

How do you properly maintain a car's cooling system?

• Check coolant level

• Inspect radiator and hoses for leaks/damage

• Flush the cooling system when needed

Why is using the correct coolant important?

The correct coolant helps the engine regulate temperature and prevents cooling system problems.

What can happen if the cooling system is neglected?

A neglected cooling system can cause engine overheating, which may lead to engine damage and expensive repairs.

What is the purpose of an engine lubrication system?

The lubrication system sends oil to moving engine parts to reduce:

• Friction

• Heat

• Wear

What are the two main types of engine lubrication systems?

• Wet sump

• Dry sump

How does a wet sump lubrication system work?

A wet sump stores oil in a pan at the bottom of the engine. A pump sends oil through a filter and engine passages to lubricate moving parts.

What does an oil filter do?

removes contaminants and debris from the oil before it circulates through the engine.

How does a dry sump lubrication system store oil?

A dry sump stores oil in a separate tank outside of the engine instead of an oil pan inside the engine.

What does the scavenge pump do in a dry sump system?

The scavenge pump removes oil from the engine sump and sends it to the external oil tank.

What does the pressure pump do in a dry sump system?

The pressure pump sends oil from the external tank through the filter and back into the engine.

What is the advantage of a dry sump system?

A dry sump provides better oil control and oil flow, especially during high-performance driving.

What does the oil pan do?

stores the engine oil and acts as the oil reservoir.

What does the oil pump do?

moves oil from the oil pan to the engine parts that need lubrication.

What does the oil filter do?

removes contaminants and debris from the oil before it circulates through the engine.

What are oil galleries or passages?

channels inside the engine block that direct oil to moving engine parts.

What does the pressure relief valve do?

controls oil pressure by opening when oil pressure becomes too high.

where is the pressure relief valve located?

The valve is located within the oil pump or oil filter and is designe dot opne when teh oil pressure in th engine exceeds a certian level.

What is the path of oil through an engine lubrication system?

Oil pan → Oil pump → Oil filter → Oil galleries/passages → Engine parts → Back to oil pan

What does engine oil do besides lubricate parts?

• Reduces friction and wear

• Carries away heat

• Helps protect engine components

Why are regular oil changes important?

Oil changes remove old, contaminated oil and help keep the lubrication system working properly.

What is the main function of engine oil?

reduces friction between moving engine parts, allowing the engine to run smoothly.

How does engine oil help seal the engine?

Oil creates a seal between the piston, piston rings, and cylinder walls, helping keep combustion gases inside the cylinder.

How does engine oil help clean the engine?

Oil additives trap and suspend contaminants, allowing the oil filter to remove them.

What other benefit does engine oil provide?

Engine oil helps reduce engine noise and allows smoother operation.

What are the two main components of engine oil?

• Base oil (mineral or synthetic oil)

• Additives that improve performance

What do oil additives do?

They improve its preformance; detergents, viscosity miodifiers, and anti-wear agents

Why is using the correct engine oil important?

correct engine Oil reduces wear and protects engine

What can happen if the wrong or poor-quality oil is used?

damage/performance problems

What is engin oil rated by?

Viscosicty

What is viscosity?

the oil’s resistance to flow at a certain temperature.

What does a lower oil viscosity number mean?

A lower number means thinner oil that flows more easily.

What does a higher oil viscosity number mean?

A higher number means thicker oil that flows less easily.

What does SAE 5W-30 describe?

SAE 5W-30 describes an oil’s viscosity at different temperatures:

• 5W = cold temperature flow

• 30 = high temperature viscosity

Why is diesel engine oil different from gasoline engine oil?

Diesel oil has more detergents and additives because diesel engines produce more soot and contaminants and operate at higher temperatures and pressures.