310S Fuel and Emission Systems 1 — Questions and Answers
Question 1: What is the stoichiometric air-fuel ratio for gasoline engines?
- 12.5:1
- 14.7:1 (Correct answer)
- 16.2:1
- 10.0:1
Correct answer: 14.7:1
The stoichiometric ratio of 14.7:1 (14.7 parts air to 1 part fuel by mass) provides the chemically ideal mixture for complete combustion and optimal catalytic converter efficiency.
Question 2: What does a wideband oxygen sensor measure that a narrowband sensor cannot?
- Exhaust gas temperature
- The exact air-fuel ratio across a wide range rather than just rich or lean of stoichiometric (Correct answer)
- The concentration of NOx in the exhaust
- Catalytic converter internal temperature
Correct answer: The exact air-fuel ratio across a wide range rather than just rich or lean of stoichiometric
Wideband (air-fuel ratio) sensors measure the precise lambda value across a wide range (typically 10:1 to 23:1), unlike narrowband sensors that only toggle between rich and lean near stoichiometric.
Question 3: What is the function of the evaporative emission (EVAP) system?
- To recirculate exhaust gases back into the intake
- To capture and store fuel vapours from the fuel tank and purge them into the engine for combustion (Correct answer)
- To cool the fuel before it enters the injectors
- To filter particulate matter from the exhaust
Correct answer: To capture and store fuel vapours from the fuel tank and purge them into the engine for combustion
The EVAP system prevents hydrocarbon fuel vapours from escaping to the atmosphere by storing them in a charcoal canister and purging them into the intake manifold to be burned during normal driving.
Question 4: What component controls the amount of fuel delivered by a port fuel injector?
- The fuel pressure regulator only
- The ECM controlling the injector pulse width (on-time) (Correct answer)
- The throttle position sensor directly
- The fuel pump speed
Correct answer: The ECM controlling the injector pulse width (on-time)
The ECM controls fuel delivery by varying the injector pulse width — the duration the injector solenoid is energized. Longer pulse width delivers more fuel; shorter delivers less. Fuel pressure is held constant by the regulator.
Question 5: What does a catalytic converter do to reduce harmful emissions?
- It filters particulate matter from the exhaust stream
- It uses precious metal catalysts to chemically convert CO, HC, and NOx into less harmful CO2, H2O, and N2 (Correct answer)
- It cools exhaust gases before they exit the tailpipe
- It recirculates a portion of exhaust back into the intake
Correct answer: It uses precious metal catalysts to chemically convert CO, HC, and NOx into less harmful CO2, H2O, and N2
A three-way catalytic converter uses platinum, palladium, and rhodium catalysts to oxidize CO and HC into CO2 and H2O, and reduce NOx into N2 and O2, significantly lowering tailpipe emissions.
Question 6: What is the purpose of the exhaust gas recirculation (EGR) valve?
- To increase engine power at high RPM
- To reduce combustion temperatures and lower NOx emissions by introducing inert exhaust gas into the intake (Correct answer)
- To improve fuel economy at idle
- To prevent exhaust leaks at the manifold
Correct answer: To reduce combustion temperatures and lower NOx emissions by introducing inert exhaust gas into the intake
The EGR valve meters a controlled amount of inert exhaust gas into the intake charge, displacing oxygen and lowering peak combustion temperatures, which reduces the formation of nitrogen oxide (NOx) emissions.
310S Fuel and Emission Systems 1
What is the stoichiometric air-fuel ratio for gasoline engines?