ASE Fuel Systems & Emissions Control

Question 1

What is the stoichiometric air-fuel ratio for a gasoline engine?

Accepted Answer

14.7:1

Answer

The stoichiometric ratio of 14.7:1 represents the ideal mixture for complete combustion, producing the fewest harmful emissions while maximizing efficiency.

Question 2

What is the primary purpose of the EVAP (Evaporative Emission Control) system?

Accepted Answer

Prevent fuel vapors from escaping into the atmosphere

Answer

The EVAP system captures fuel vapors from the fuel tank, stores them in a charcoal canister, and routes them into the engine to be burned rather than venting to the atmosphere.

Question 3

Which sensor provides the primary feedback signal to the ECM for closed-loop fuel control?

Accepted Answer

Oxygen (O2) sensor

Answer

The upstream oxygen sensor measures residual oxygen in the exhaust, giving the ECM real-time feedback to adjust injector pulse width and maintain the stoichiometric 14.7:1 ratio.

Question 4

What does a MAF (Mass Airflow) sensor measure?

Accepted Answer

The mass of air entering the engine per unit of time

Answer

The MAF sensor measures the actual mass of air entering the intake manifold, enabling the ECM to calculate precise fuel delivery amounts for any operating condition.

Question 5

What is the primary purpose of the EGR (Exhaust Gas Recirculation) system?

Accepted Answer

Reduce NOx emissions by lowering peak combustion temperatures

Answer

The EGR system dilutes the intake charge with inert exhaust gases, lowering peak combustion temperatures below the threshold at which NOx forms (approximately 2,500°F).

ASE Practice Test

ASE Practice Test

ASE Fuel Systems & Emissions Control