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Engine Performance & Tuning Flashcards

7 cards from real CTE practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

Read the first 7 Engine Performance & Tuning flashcards as text

  1. What is the primary teaching point when discussing lambda (λ) values in engine combustion?

    Answer: Lambda = 1.0 represents stoichiometric combustion; values above 1.0 are lean and below 1.0 are rich

    Lambda normalizes the actual AFR against stoichiometric AFR, providing a fuel-type-independent measure of mixture richness or leanness.

  2. During an OBD-II scan, a P0171 (System Too Lean, Bank 1) code is stored. Which component failure is LEAST likely to cause this code?

    Answer: Leaking fuel injector on Bank 1

    A leaking (over-fueling) injector would cause a rich condition, not a lean one; all other options reduce fuel delivery or add unmetered air.

  3. What CTE safety practice should always precede fuel system pressure testing?

    Answer: Relieve fuel system pressure and ensure no ignition sources are present

    Fuel systems remain under pressure after shutdown; relieving pressure and eliminating ignition sources prevents fire or injury during testing.

  4. Which condition would cause an engine's idle speed to hunt (fluctuate up and down) repeatedly?

    Answer: Erratic or dirty idle air control (IAC) valve or dirty throttle body

    A sticky or dirty IAC valve cannot precisely regulate bypass air, causing the ECU to over- and under-correct, creating a hunting idle.

  5. What does increasing a fuel injector's pulse width (duty cycle) accomplish?

    Answer: Delivers more fuel per injection event, enriching the mixture

    Pulse width controls how long the injector remains open; a longer pulse width means more fuel is delivered per cycle.

  6. A student tests a fuel pressure regulator and finds fuel pressure drops immediately when the engine is shut off. This indicates:

    Answer: A leaking fuel pressure regulator or check valve allowing pressure bleed-down

    Pressure should hold for several minutes after shutdown; rapid bleed-down points to a leaking regulator, check valve, or injector.

  7. When teaching students about port fuel injection (PFI) vs. gasoline direct injection (GDI), which is a known disadvantage of GDI engines?

    Answer: Carbon buildup on intake valves because fuel does not wash the valve stems

    In GDI engines, fuel never contacts intake valves, so combustion deposits accumulate on valve stems and seats, restricting airflow over time.