ASVAB: Auto Information Review

The Internal Combustion Engine Systems

Internal Combustion Engines
Combustion is the chemical reaction between fuel and air to release energy; spark ignition (SI)/gasoline internal combustion engines ignite gasoline (or a gasoline mixture) and air with a spark to do work. Diesel engines are also internal combustion engines, but they utilize compression ignition (CI) to ignite diesel, rather than a spark for gasoline.
Core engine components are housed in the engine block.
Most gasoline engines operate with reciprocating pistons in cylinders. They use either a four-stroke or a two-stroke cycle, and most automobiles in the United States utilize the four-stroke cycle.
Four piston strokes make up the four-stroke cycle: intake, compression, power, and exhaust. In one cycle, the piston moves down and back up twice.

Electrical System
When a driver turns a key (or pushes a button) to start a car, an electrical circuit is completed. Electricity runs from the battery to the starter motor (starter), which turns the crankshaft. In turn, the engine uses a pully system to turn the alternator, which recharges the battery and produces most of the electricity to the vehicle while it runs. The solenoid acts as a heavy-duty relay between the battery and the starter motor.
The electrical system also simultaneously fires up the fuel pump (in newer cars) and spark plugs (via a coil).

Common Electrical Problems
If a car won't start when the key is turned, this could be the result of a dead battery, faulty battery connections, or a problem with the starter motor or solenoid. If the alternator is bad, this may lead to a battery without a charge or headlights that are dim at low engine speeds.
Battery connections can be checked and improved by cleaning off corrosion with a wire brush and applying specialized grease to prevent further corrosion. A dead battery can be jumped to attempt to get the car running and help troubleshoot electrical problems. If it won't jump start, the problem might be with the starter; if it will start but won't stay running, the problem could be with the battery; if it will start and stays running, the problem could be with the alternator, or a light might have been left on in the vehicle.

Fuel System
When a gasoline car is started, the electrical system starts the fuel system, which stores and delivers fuel (gasoline or gasoline mixture, in this case) to the engine. In newer cars, the fuel pump is housed in the fuel tank. Fuel filters protect fuel injectors or carburetors by ensuring clean fuel, and they can be found on either side of the fuel pump.
In newer cars, computer-controlled fuel injectors atomize fuel into the cylinder (part of the engine) through a tiny electric valve in order to feed the combustion process; the computerization allows for better fuel economy and lower emissions. Older vehicles use carburetors, which mix fuel and air without a computer.

Common Fuel System Problems
Fuel filters can clog and should be replaced at regular intervals. Clogged filters can prevent the vehicle from starting or cause it to sputter when traveling at high speed. Faulty fuel pumps can also prevent the car from starting: this could be an electrical problem or a problem with the pump itself due to regular wear-and-tear, contamination, or overheating. Fuel injectors can also clog, even with regular changing of the fuel filter. Signs of dirty or clogged injectors include increased emissions, decreased fuel economy, and poor idling and performance.

Ignition System: the ignition system, and the two systems are closely linked. Ignition is the generation of a spark or heating of an electrode to initiate combustion of fuel and air.  The battery provides low voltage to a coil, which acts as a transformer and electromagnetically converts it to high voltage for use by the corresponding spark plug. Spark plugs force electricity to jump between electrodes across a gap, creating a spark. The alternator continues to produce electricity while the car is running, which allows the spark plugs to continue firing. There is one spark plug per cylinder in a spark-ignition internal combustion engine.

Common Ignition Problems
One of the most common ignition problems is spark plug fouling, which occurs when carbon builds up at the ignition point; it will cause engine misfiring and increased carbon emissions.
Driving at highway speeds is good for spark plugs because the increased temperature of the engine helps burn off the excess fuel or ash. Spark plug fouling is more common with prolonged idling and city driving because the engine doesn't get as hot.
Common signs of faulty ignition coils include: backfiring as a result of excess fuel in the combustion chamber, poor fuel economy, vibration when idling, and stalling.

Engine System

Piston and Cylinder
Most gasoline engines utilize a reciprocating piston and cylinder system for combustion, which functions to combust fuel (in this case, gasoline) and air. Pistons, together with their rings, act as plungers to take in and compress gas within the cylinder.
Pistons are connected to the crankshaft via a hinged connecting rod. The
combustion chamber is the space created by piston where fuel and air mix and are ignited by the spark plug. Fuel delivery occurs by way of either a fuel injector or a carburetor.



Engine Block
Once the gasoline vehicle is started, the electrical, fuel, and ignition systems converge in the engine. The electrical system started turning the crankshaft, fuel injectors atomized gasoline pre-combustion, and spark plugs created a spark.
The valvetrain coordinates opening and closing of valves so that air-fuel entry and exhaust release is timed properly. The camshaft is a rotating shaft surrounded by oil with cams (specially shaped nodes) that depress or allow the release of the intake and exhaust valves as they rotate with the shaft. Intake valves regulate air-fuel mixture entry into the combustion chamber. Exhaust valves release gas byproducts of combustion to the exhaust manifold.
The crankcase is full of oil and houses the crankshaft and connecting rods. Each piston is hinged to a connecting rod, which is hinged to the crankshaft. The crankshaft rotates by combined, alternating motion of the pistons and their connecting rods. As is rotates, the crankshaft drives the camshaft by way of a timing belt or chain and gears.



Common Engine Problems
Problems with the engine and process of combustion can occur within the piston and cylinder unit or with the components that coordinate their functions. A broken or faulty timing belt will likely result in a ticking noise from the engine and will cause the vehicle to rough idle or misfire. It can also lead to a decrease in oil pressure, smoke coming from the engine, or broken pistons or valves. Crankshaft problems will lead to difficulty starting the vehicle or intermittent stalling; camshaft problems may cause rough idling, frequent stalling, poor fuel economy, slow accelerations, and difficulty starting. If the piston rings fail, oil will leak into the combustion chamber, causing the engine to smoke. Backfiring occurs when combustion takes place outside of the cylinders and can be the result of bad engine timing or improper fuel-air mixture ratios.

Exhaust System
The exhaust system transports gas products (exhaust) from the combustion process away from the engine and the vehicle. Exhaust from the combustion chamber is released by the exhaust valve towards the exhaust manifold, which collects gas byproducts from each cylinder and helps with noise control. Through the exhaust pipe, gas travels to the catalytic converter, which filters out pollutants and converts them to water vapor and carbon dioxide. From the catalytic converter, exhaust travels through the exhaust pipe to the muffler, which further reduces noise. From the muffler, the tail pipe releases gas away from the vehicle.

Common Exhaust Problems
Consistently short trips of less than 15 miles, such as driving in town without getting on the highway, don't allow the water condensed in the exhaust system to vaporize and escape, which can cause corrosion and rusting of the exhaust system.
Fluids such as coolant or oil can leak from the engine if there is a faulty gasket and clog the catalytic converter, causing poor engine performance or preventing it from running properly. Excessive heat or unused fuel coming off the engine can cause the catalytic converter to overheat. Other symptoms of catalytic converter trouble include: reduced acceleration, dark exhaust smoke, more heat than usual under the vehicle, or exhaust that smells like sulfur.

Lubrication System
Motor oil is used to prevent friction and corrosion within the engine. The oil pan is below the engine block and holds oil for pressurized distribution by the oil pump through the oil galleries, specialized channels throughout the engine. An oil filter helps keep the oil free of debris so that the moving parts in the engine don't get clogged. In addition to the galleries, the camshaft and the crankshaft are lubricated by motor oil; piston rings keep oil below the piston head and out of the combustion chamber.

Common Lubrication problems
Besides friction reduction, oil also keeps the engine parts clean, and vehicles should have the oil and oil filter changed every 3,000 miles to prevent overheating and wearing out of the engine. Motor oil is labelled with viscosity ratings at both low temperatures (example: 5W or 10W) and high temperatures (SAE 30 or SAE 40) so that it will be thin enough to be functional when it is very cold outside and thick enough when the engine is very hot. Synthetic motor oil is manufactured and is more consistent and will last longer than conventional motor oil.

Cooling System
While running, the average engine temperature is 180°F; the walls of the cylinders are between 350°F and 600°F, and the combustion chamber is roughly 3000°F. The cooling system helps keep the engine running within its ideal temperature range without overheating. Coolant, commonly made up of half antifreeze and half water, prevents overheating by circulating through channels throughout the engine by way of the water pump. The thermostat helps control engine temperature by sending coolant either to the engine or to the radiator if it needs to be cooled further. The radiator is a series of thin channels that allow air to remove heat from the coolant, aided by the cooling fan.

Common Cooling Problems
Problems with the cooling system can lead to engine overheating and damage. Broken or cracked coolant or radiator hoses can allow coolant to leak. Coolant breaks down over time and should be replaced according to the schedule given by the vehicle manufacturer. A thermostat stuck open will cause the engine to run cold and result in bad gas mileage; a thermostat stuck closed will cause the engine to overheat. The water pump and radiator cap both maintain the correct pressure range of the coolant in the system; a problem with either will prevent proper temperature regulation and lead to overheating.
A broken or faulty fan belt or cooling fan will prevent the pumping of air into the radiator; if the car overheats, both should be checked for proper function.

Chassis Systems

Drivetrain System
The drivetrain translates power from the engine in order to move the vehicle forward. The crankshaft is attached to the flywheel, which stores rotational energy from the engine and smooths the motion of the pistons. The clutch allows for disengaging and re-engaging of the transmission and the flywheel/engine so that stopping the motion of the wheels doesn't also stop the engine. The transmission multiplies engine torque to allow for a wide range of vehicle speeds, as well as acceleration and deceleration; it consists of a series of gears, and more gears translate to better engine efficiency.  Most modern transmissions are automatic, but they can also be manual or constant velocity (CV). The differential splits the torque of the engine to allow the inside and outside wheels to spin at different speeds, as when turning.

Drivetrain Configurations
Drivetrains power the turning of the wheels of the vehicle through the transmission and axles in the following configurations:
Rear wheel drive (RWD) is found in trucks and older cars, and the transmission delivers power to the rear axle via the driveshaft.
·        
Front wheel drive (FWD) is found in most modern economy or compact cars; the transaxle combines the functionality of the transmission, front axle, and differential into one component. The engine weight is over the drive wheels, which allows for better traction.
All wheel drive (AWD) is in most newer cars and SUVs and powers both axles using a transfer case, which distributes the engine torque to both the front and rear axles.
Four-wheel drive (4WD) utilizes a specialized transfer case to accommodate different driving conditions: Two-wheel drive (2WD) offers better gas mileage for city and highway driving; four-wheel drive high (4WD-HI) allows for intermediate torque for off-road driving at higher speeds; four-wheel drive low (4WD-LO) provides maximum torque for off-road driving at lower speeds.

Common Drivetrain System Problems
In a manual transmission, hard shifting or grinding may be the result of clashing gears and worn out synchronizers. Automatic transmissions also wear out, which leads to transmission slipping and poor shifting. Transmission fluid should also be changed and levels maintained to prevent gear slippage and shifting problems. The clutch can jam, which may cause violent vehicle shaking and overheating in the transmission. Transfer case problems can lead to difficulty shifting gears, grinding noises, or jumping in and out of four-wheel drive.

Suspension System
The suspension system allows for a smooth, comfortable ride when driving, prevents components from stress or vibrating loose, keeps the vehicle upright, and allows for pivoting when steering. Springs, installed between the chassis or frame and the axels, absorb the impact of the road on the vehicle; most vehicles use coil springs or layered leaf springs:


Shocks (shock absorbers or dampers) oppose the oscillating motion of the springs and dampen road vibration. Struts are a combination of springs and shocks. The anti-roll bar or sway bar keeps the vehicle from rolling over when turning and allows for better handling. The spindles, which should be parallel to the ground, are the center point of each wheel that connects to the upper and lower control arms via a sealed and greased ball joint. Control arms connect the suspension system to the frame of the vehicle through bushings, which are insulated joint linings that protect the jointed components from vibration or wear.

Common Suspension Problems
Worn shocks and struts can cause excessive bumping and bouncing, and oil leaking from either is a sign of wear. The bushings of the sway bar can also wear out, signaled by thumping or knocking when turning or taking bumps. Pickup trucks should normally sit with their bed slightly higher than the body of the truck to allow for heavy loads; if it sits level (without modifications), it could be a sign of a faulty spring. The same is true if one corner of the vehicle sits lower than the rest while on level ground.

Steering System
The steering system directs the vehicle while driving and minimizes the force required for such movement. The steering system engages either the modern, highly precise rack-and-pinion system or the older, less precise steering-box system to translate the turning of the steering wheel via small gears to the front wheels. Power steering supplies pressurized engine oil from a pump to the steering rack or steering box so that steering is easier and more responsive.
Car alignment, though it involves the suspension system, impacts vehicle steering; proper alignment is required for the vehicle to continue to travel straight when the steering wheel is temporarily released.

Common Steering Problems
Power steering fluid sometimes gets low and needs to be refilled. However, hoses associated with the steering system, like all vehicle hoses, can wear and crack over time and lead to leaking power steering fluid and require replacement. Low or leaking power steering fluid, a problem with the power steering pump, and even some suspension problems such as worn control arm bushings can result in difficulty turning the steering wheel and steering the vehicle. Power steering problems can also cause a grinding or squealing noise when turning. Improper alignment can also cause passive steering problems: when the steering wheel is temporarily released, the vehicle will pull to one side.

Brake System
The brake system is vital for motorist safety as it allows for slowing and stopping, even at high speeds. When the brake pedal is depressed, brake fluid is pushed from the master cylinder through the brake lines to each wheel's brake caliper. The fluid pressure causes friction, which forces the wheels to stop turning.
Most vehicles have disc brakes on the front wheels, and some have them on the rear wheels, as well. When the brake fluid flows through the brake lines, it depresses a piston in the brake caliper, which squeezes the inner and outer brake pads, which are materially hard and designed to withstand heat and friction. Brake pads squeeze against the cast iron disc rotor, which is held to the wheel at the wheel hub.
Vehicles that do not have disc brakes on the rear tires use drum brakes. The wheel cylinder forces the paired brake shoes against the inside walls of the bowl-shaped, cast iron drum.

Common Brake Problems
Brake pads encounter lots of friction, wear out and need to be replaced; symptoms of this include grinding and squealing when the brake pedal is applied and taking longer to stop. Rotors also encounter a lot of friction and can warp. If the vehicle experiences pulsing when slowing or stopping, it might be due to warped rotors. Sponginess or softness when the brake pedal is applied could signal a problem with the master cylinder or low brake fluid levels and requires immediate attention. If the car pulls to one side when braking, the brake calipers might not be applying equal pressure to the tires. A stuck brake caliper or engaged parking brake while driving can lead to overheating, will likely cause a sharp odor, and should also be addressed immediately.