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ASE Medium / Heavy Truck

T1 Gasoline Engines — practice test

Studying for T1 (Gasoline Engines)? Overhaul Prep has 118 verified T1 questions written to the current task list — in the same formats the real exam uses (direct, Technician A/B, EXCEPT and most-likely-cause). Every answer comes with a written explanation, so you learn why instead of memorising a letter.

118T1 questions
100%with explanations
9,711questions in total
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Sample T1 questions

Straight from the bank — answers highlighted, with the explanation underneath.

A spark-ignition (gasoline) engine's air/fuel ratio for best emissions control (stoichiometric) is approximately:

  1. 10:1
  2. 14.7:1
  3. 20:1
  4. 25:1
Why14.7:1 (by mass) is stoichiometric for gasoline — the ratio that lets the three-way catalyst work most efficiently. The oxygen/air-fuel sensors keep the mixture oscillating around this point in closed loop.

Technician A says a heated oxygen sensor in a properly operating closed-loop system should cross between roughly 0.1 and 0.9 volts several times per second. Technician B says an O2 sensor voltage stuck at a steady 0.45 volts can be caused by the sensor staying in open loop or being biased by the PCM. Who is correct?

  1. Technician A only
  2. Technician B only
  3. Both Technicians A and B
  4. Neither Technician
WhyBoth are correct. A healthy narrow-band O2 sensor rapidly switches between about 0.1V (lean) and 0.9V (rich), and a steady ~0.45V is the PCM bias voltage seen in open loop or with an inactive sensor.

A port-fuel-injected gasoline engine cranks but will not start. Fuel pressure reads normal with key on, but drops to zero within seconds after the pump stops. The MOST likely cause is:

  1. A leaking fuel pump check valve or leaking injector
  2. A restricted fuel return line
  3. An open fuel pump relay coil
  4. A stuck-closed thermostat
WhyRapid pressure bleed-down after the pump shuts off indicates a leaking check valve (in the pump) or a leaking injector/regulator. A restricted return line would tend to raise or hold pressure, and a thermostat is unrelated to fuel pressure.

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