Automotive and Mechanics Fuel Systems & Combustion 1 — Questions and Answers
Question 1: What is the stoichiometric air-fuel ratio for gasoline engines?
- 12.5:1
- 14.7:1 (Correct answer)
- 16.1:1
- 10.3:1
Correct answer: 14.7:1
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?
- Fuel pump
- Fuel pressure regulator (Correct answer)
- Fuel filter
- Fuel rail
Correct answer: Fuel pressure regulator
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?
- Vacuum leak
- Faulty MAF sensor reading high (Correct answer)
- Clogged fuel injector
- Low fuel pressure
Correct answer: Faulty MAF sensor reading high
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?
- Eliminates the fuel pressure regulator entirely
- Keeps fuel in the tank cooler by not returning hot fuel (Correct answer)
- Allows higher fuel pressure
- Reduces the number of injectors needed
Correct answer: Keeps fuel in the tank cooler by not returning hot fuel
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?
- Port fuel injection
- Throttle body injection
- Direct injection (Correct answer)
- Multi-point injection
Correct answer: Direct injection
Direct injection (GDI) sprays fuel directly into the combustion chamber at high pressure, improving efficiency and power.
Question 6: What does a knock sensor detect in an engine?
- Camshaft position
- Abnormal combustion (detonation) (Correct answer)
- Exhaust backpressure
- Fuel rail pressure
Correct answer: Abnormal combustion (detonation)
A knock sensor detects detonation or pre-ignition vibrations and signals the ECU to retard ignition timing.
Automotive and Mechanics Fuel Systems & Combustion 1
What is the stoichiometric air-fuel ratio for gasoline engines?