Auto Information Practice Test 4: Engines to Electrical

Answer: D

Correct answer: To store the fuel supply safely and sealed. The fuel tank stores fuel and keeps it sealed, with vent connections that capture vapors. Pumping, filtering and metering are done by other parts, even if some are mounted inside the tank.

• A: Raising pressure is the fuel pump's job; the pump may sit inside the tank, but it is a separate part.
• B: Fuel metering is done by the injectors under ECM control, not by the tank.
• C: Removing particles is the job of the fuel filter or pump strainer, not the tank itself.
• D (correct): The tank is a storage container that holds fuel and keeps it sealed against leaks and vapor escape.

Answer: D

Correct answer: It carries hydraulic pressure that applies clutches and bands. Automatic transmission fluid transmits power in the torque converter, carries hydraulic pressure to apply clutches and bands, lubricates and cools. Because shifts depend on that pressure, low or worn fluid can cause slipping or harsh shifts.

• A: Engine coolant, not transmission fluid, cools the cylinder heads and block.
• B: Brake calipers are applied by brake fluid from the master cylinder, a separate system.
• C: Ignition timing is controlled by the ignition system, not by transmission fluid.
• D (correct): Shifting in an automatic depends on fluid pressure applying the clutches and bands.

Answer: B

Correct answer: 5400. First find power strokes per cylinder, then multiply by the number of cylinders.

• A: This counts one power stroke per revolution in each cylinder, forgetting that a four-stroke cylinder fires only every two turns.
• B (correct): Each cylinder fires 3600 divided by 2, or 1800, times a minute; three cylinders give 5400.
• C: This is the count for one cylinder; it still needs to be multiplied by three.
• D: This divides the rpm by the number of cylinders instead of multiplying the per-cylinder rate by it.

Answer: B

Correct answer: Electronic stability control. The clues are steering angle, yaw rate and sideways acceleration, used to keep the car pointed where the driver steers. That describes electronic stability control, which shares wheel-speed sensors and the modulator with ABS and traction control but solves a different problem.

• A: ABS prevents wheel lock during braking; it does not use yaw rate to correct a skid in a curve.
• B (correct): Stability control compares where the driver is steering with how the car is actually turning and brakes individual wheels to correct it.
• C: Traction control limits wheel spin during acceleration by braking the spinning wheel or cutting engine power.
• D: A proportioning valve limits rear brake pressure during stops; it has no steering or yaw sensors.

Answer: D

Correct answer: About 78.5 kW. Multiply torque by crankshaft speed, then divide by 9549.

• A: This halves the speed to 2500 rpm, as if the 2:1 cam rule applied; power uses the crankshaft speed directly.
• B: This is a decimal slip, ten times too small; recheck the division of 750,000 by 9549.
• C: This doubles the correct result, as if the torque were 300 N·m.
• D (correct): 150 times 5000 is 750,000, and 750,000 divided by 9549 is about 78.5 kW.

Answer: D

Correct answer: A coolant leak; inspect and check the level when cold. Coolant is often orange, green, pink or blue and smells sweet, and a coolant leak lowers the reservoir level. Look for the highest wet point around the pump and hoses, and check the level only when the engine is cold, since a hot system can spray scalding coolant.

• A: A/C drain water is clear and odorless, and it does not lower the coolant reservoir.
• B: Engine oil is not orange or sweet smelling, and a dropping coolant tank points to the cooling system.
• C: Brake fluid is not found near the water pump, and the falling coolant level points to the cooling system instead.
• D (correct): Colored, sweet-smelling fluid near the water pump plus a falling reservoir level points to coolant, and the level must be checked only with the engine cold.

Answer: C

Correct answer: The rotor loses its field current, so the alternator produces little or no output. The rotor is an electromagnet that gets its small field current through brushes and slip rings. Its spinning field induces AC in the stator, which the diodes rectify. With no brush contact there is no rotor field, so there is no induced voltage and the charging system stops charging.

• A: Output depends on the rotor's magnetic field; removing field current lowers output instead of raising it.
• B: The brushes are the path for rotor field current, so they are essential to charging.
• C (correct): Brushes carry field current to the spinning rotor; without a magnetic field, nothing is induced in the stator.
• D: The diodes are a separate part; the problem is that little or no AC is being made at all.

Answer: A

Correct answer: A wax pellet that expands as it heats and pushes the valve open. A typical thermostat contains a wax pellet. When coolant reaches the rated temperature, often around 180 to 200°F, the wax expands and pushes the valve open so coolant can flow to the radiator.

• A (correct): The wax expands at the thermostat's rated temperature and moves the valve.
• B: The fan relay controls the fan, not a conventional thermostat valve.
• C: The cap's pressure affects boiling point; a typical thermostat responds to temperature, not cap pressure.
• D: Pump speed changes flow, but a typical thermostat opens because of temperature, not rpm.

Answer: D

Driving warms the air in a tire, so warm readings normally run a few psi above the cold value, as the 37 psi tires show. The left rear reads 30 psi even while warm, so its cold pressure would be lower still. The TPMS lamp only warns at about a 25 percent drop, so it can stay off. Recheck the tire cold, inflate it to 34 psi and have it inspected for a leak.

• A: The 4 psi comparison ignores heating; a warm reading below the cold target means the cold pressure is lower still.
• B: Pressure rises with heat, so letting air out of hot tires would leave them low when cold.
• C: Heating raises pressure, not lowers it, so this reasoning is backward.
• D (correct): Warm tires normally read above the cold value, as the three 37 psi tires do, so a warm 30 psi points to a tire that is truly low.

Answer: C

Correct answer: 180 J. Energy in a spring is

so it scales with the square of the compression. Going from 3 cm to 9 cm triples x.

• A: This assumes energy grows in direct proportion to compression, but energy depends on x².
• B: This uses the extra 6 cm as a doubling (×4) instead of comparing 9 cm with 3 cm.
• C (correct): Tripling the compression multiplies the energy by 3² = 9, and 20 × 9 = 180 J.
• D: This cubes the factor (3³ = 27) instead of squaring it.