NCED Engine Performance & Tuning 3

Question 1

What is the primary function of an OBD-II port on a modern vehicle?

Accepted Answer

To allow diagnostic tools to communicate with the vehicle's ECU and read fault codes

Answer

The OBD-II (On-Board Diagnostics II) port is a standardized interface that allows scan tools to access ECU data, read diagnostic trouble codes (DTCs), and monitor live sensor data.

Question 2

A wideband oxygen sensor differs from a narrowband sensor because it:

Accepted Answer

Measures AFR accurately across a wide range, not just near stoichiometry

Answer

Wideband O2 sensors (LSU-type) produce a linear signal across a broad AFR range (e.g., 10:1 to 20:1), making them essential for precise ECU tuning and closed-loop control.

Question 3

What is the purpose of a fuel pressure regulator?

Accepted Answer

To maintain consistent fuel pressure at the injectors regardless of engine load

Answer

The fuel pressure regulator ensures injectors receive a stable, consistent pressure differential so that injector pulse width accurately controls fuel quantity delivered.

Question 4

A Throttle Position Sensor (TPS) sends what information to the ECU?

Accepted Answer

The angle/position of the throttle plate opening

Answer

The TPS tells the ECU how far open the throttle plate is, which the ECU uses alongside other sensors to determine driver demand and adjust fuel, ignition timing, and transmission shift points.

Question 5

What does a chassis dynamometer (dyno) measure during engine tuning?

Accepted Answer

Wheel horsepower and torque output under controlled conditions

Answer

A chassis dyno measures power and torque at the driven wheels while the vehicle is stationary, allowing tuners to evaluate the effect of ECU map changes in real time.

(NCED) Nationally Certified Educational Diagnostician Practice Test

(NCED) Nationally Certified Educational Diagnostician Practice Test

NCED Engine Performance & Tuning 3