Automotive and Mechanics Fuel Systems & Combustion 2

Question 1

What is the function of the evaporative emission control (EVAP) system?

Accepted Answer

Prevent fuel vapors from escaping to the atmosphere

Answer

The EVAP system captures fuel vapors from the tank and routes them to the intake manifold to be burned, reducing hydrocarbon emissions.

Question 2

Which sensor provides the ECU with feedback to adjust the air-fuel ratio in closed-loop operation?

Accepted Answer

Oxygen sensor

Answer

The oxygen (O2) sensor measures exhaust oxygen content and feeds back to the ECU to fine-tune the air-fuel mixture in closed-loop mode.

Question 3

What does a high long-term fuel trim (LTFT) positive value indicate?

Accepted Answer

ECU is adding fuel to compensate for a lean condition

Answer

A positive LTFT value means the ECU is adding fuel, indicating the engine is running lean, often due to a vacuum leak or weak fuel pressure.

Question 4

What is the purpose of a fuel pressure dampener?

Accepted Answer

Reduce pressure pulsations from the fuel pump

Answer

A fuel pressure dampener absorbs pulsations created by the high-pressure fuel pump, ensuring smooth, consistent fuel delivery.

Question 5

Which component in a carbureted engine controls the amount of fuel mixed with air at idle?

Accepted Answer

Idle mixture screw

Answer

The idle mixture screw adjusts the fuel-air ratio at idle by controlling how much fuel bleeds into the idle circuit.

Automotive and Mechanics Practice Test