Automotive and Mechanics Fuel Systems & Combustion

Question 1

What is the stoichiometric air-fuel ratio for gasoline engines?

Accepted Answer

14.7:1

Answer

The stoichiometric air-fuel ratio for gasoline is 14.7:1, meaning 14.7 parts air to 1 part fuel for complete combustion.

Question 2

Which fuel system component regulates fuel pressure delivered to the injectors?

Accepted Answer

Fuel pressure regulator

Answer

The fuel pressure regulator maintains consistent fuel pressure to the injectors, typically between 35–65 psi depending on the system.

Question 3

What causes a rich air-fuel mixture condition in a fuel-injected engine?

Accepted Answer

Faulty MAF sensor reading high

Answer

A MAF sensor reading higher than actual airflow causes the ECU to inject excess fuel, creating a rich mixture.

Question 4

What is the purpose of a returnless fuel system?

Accepted Answer

Keeps fuel in the tank cooler by not returning hot fuel

Answer

Returnless fuel systems keep hot fuel from cycling back to the tank, reducing vapor lock and evaporative emissions.

Question 5

Which type of fuel injection sprays fuel directly into the combustion chamber?

Accepted Answer

Direct injection

Answer

Direct injection (GDI) sprays fuel directly into the combustion chamber at high pressure, improving efficiency and power.

Automotive and Mechanics Practice Test