Fuel Systems & Emissions Control Flashcards
7 cards from real ASE practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Fuel Systems & Emissions Control flashcards as text
What is the stoichiometric air-fuel ratio for a gasoline engine?
Answer: 14.7:1
The stoichiometric ratio of 14.7:1 represents the ideal mixture for complete combustion, producing the fewest harmful emissions while maximizing efficiency.
What is the primary purpose of the EVAP (Evaporative Emission Control) system?
Answer: Prevent fuel vapors from escaping into the atmosphere
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.
Which sensor provides the primary feedback signal to the ECM for closed-loop fuel control?
Answer: Oxygen (O2) sensor
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.
What does a MAF (Mass Airflow) sensor measure?
Answer: The mass of air entering the engine per unit of time
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.
What is the primary purpose of the EGR (Exhaust Gas Recirculation) system?
Answer: Reduce NOx emissions by lowering peak combustion temperatures
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).
What component stores fuel vapors in the EVAP system between purge events?
Answer: Activated charcoal canister
The activated charcoal (carbon) canister adsorbs and holds fuel vapors from the fuel tank until the ECM opens the purge valve to draw the vapors into the intake for combustion.
A port fuel injector is best described as a:
Answer: Electronically controlled solenoid valve that meters fuel
A fuel injector is an ECM-controlled solenoid valve; when energized, a magnetic coil lifts a pintle or ball off its seat, spraying atomized fuel for the duration of the pulse width signal.