CPT CPT Data Analysis & Interpretation 2

Question 1

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

Accepted Answer

A rich running condition requiring the ECU to remove fuel

Answer

A vacuum leak on one side of the engine

Answer

A lean condition on bank 2 only

Answer

Normal adaptive learning values

Question 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?

Accepted Answer

Normal power band characteristics related to RPM

Answer

A failing torque converter

Answer

Brake drag on the dyno rollers

Answer

Low engine oil pressure

Question 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?

Accepted Answer

Underfueling leading to lean misfire and reduced power

Answer

Overfueling and rich black smoke

Answer

Excessive ignition advance

Answer

Transmission slipping

Question 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?

Accepted Answer

Cam actuator position vs. commanded position

Answer

Coolant temperature vs. ambient temperature

Answer

Battery voltage vs. alternator output

Answer

MAP vs. barometric pressure

Question 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?

Accepted Answer

A restriction in the intake tract reducing volumetric efficiency

Answer

Normal wide-open throttle operation

Answer

A boost leak in the turbocharger system

Answer

Excessive exhaust back pressure from a clogged DPF

Question 6

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

Accepted Answer

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

Answer

They measure the same performance attribute

Answer

Trap speed is irrelevant to engine output

Answer

0-60 time is more accurate on wet tracks