CPT CPT Data Analysis & Interpretation

Question 1

When analyzing a dyno chart, a flat torque curve across a wide RPM range typically indicates what about the engine's tuning?

Accepted Answer

Optimal volumetric efficiency across the RPM band

Answer

A flat torque curve indicates the engine is producing consistent power output across RPM ranges, reflecting good volumetric efficiency and tuning.

Question 2

On a wideband oxygen sensor data log, an AFR reading consistently above 15.0:1 at wide open throttle (WOT) indicates which condition?

Accepted Answer

Lean mixture

Answer

An AFR above 15.0:1 at WOT is lean, meaning insufficient fuel relative to air, which risks detonation and engine damage.

Question 3

What does a sudden spike in short-term fuel trim (STFT) values to +25% indicate in a performance diagnostic?

Accepted Answer

The ECU is adding fuel to compensate for a lean condition

Answer

A high positive STFT means the ECU is commanding extra fuel because the oxygen sensor detects a lean exhaust condition.

Question 4

Which data parameter is MOST useful for identifying knock (detonation) events during performance testing?

Accepted Answer

Knock sensor retard counts or ignition timing pull

Answer

Knock sensor retard data directly shows how much timing the ECU is pulling to protect against detonation events.

Question 5

A technician reviews data logs and sees that volumetric efficiency (VE) drops sharply above 5,500 RPM. What is the most likely cause?

Accepted Answer

Cam phaser malfunction limiting intake duration at high RPM

Answer

A VE drop at high RPM often points to cam timing issues, restrictive intake, or cam phaser failure limiting airflow.

CPT - Certified Performance Technician Practice Test