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CPT Data Analysis & Interpretation Flashcards

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

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  1. What does a long-term fuel trim (LTFT) value of -15% on both banks indicate about the fuel system?

    Answer: A rich running condition requiring the ECU to remove fuel

    Negative LTFT means the ECU has learned to reduce fuel delivery because the engine consistently runs rich.

  2. During a WOT pull on a chassis dyno, the horsepower curve drops sharply after a peak but torque remains relatively stable. What does this typically indicate?

    Answer: Normal power band characteristics related to RPM

    HP = Torque × RPM / 5252; stable torque with falling HP at high RPM is mathematically normal as the power formula's benefit from RPM is offset by torque decline.

  3. A technician notices mass airflow (MAF) sensor readings that are lower than expected for a given throttle opening. What performance symptom would this most likely cause?

    Answer: Underfueling leading to lean misfire and reduced power

    If the MAF underreports airflow, the ECU will inject less fuel than needed, creating a lean mixture and potential misfire.

  4. Which scan tool PID would a CPT technician use to verify that a variable valve timing (VVT) system is responding correctly to load demands?

    Answer: Cam actuator position vs. commanded position

    Comparing actual cam actuator position to the commanded position verifies that the VVT solenoid and oil control valve are functioning correctly.

  5. On a data log, a technician observes that throttle position is at 100% but MAP sensor reads only 9 psi on a naturally aspirated engine. What does this suggest?

    Answer: A restriction in the intake tract reducing volumetric efficiency

    On a NA engine at WOT, MAP should approach atmospheric pressure (~14.7 psi); a low MAP indicates an intake restriction reducing cylinder filling.

  6. What is the significance of comparing 0-60 mph times against trap speed at the quarter-mile in performance testing?

    Answer: Trap speed reflects total power while 0-60 indicates launch/traction efficiency

    Trap speed is directly related to peak power output while 0-60 time reflects launch technique, traction, and gearing efficiency.