CPT Engine Performance & Tuning 2

Question 1

What does a vacuum leak downstream of the throttle body typically cause in engine operation?

Accepted Answer

Lean air-fuel mixture

Answer

A vacuum leak introduces unmetered air into the intake manifold, leaning out the air-fuel mixture beyond the intended ratio.

Question 2

Which sensor is primarily responsible for enabling closed-loop fuel control in a modern engine management system?

Accepted Answer

Oxygen sensor

Answer

The oxygen sensor provides real-time exhaust gas feedback that the ECU uses to continuously correct fuel trim and maintain stoichiometry.

Question 3

When diagnosing a misfire on a specific cylinder, swapping the ignition coil to another cylinder and observing if the misfire follows the coil indicates what?

Accepted Answer

A defective coil-on-plug unit

Answer

If the misfire moves to the new cylinder after swapping the coil, the coil itself is confirmed as the defective component.

Question 4

What is the primary function of a variable valve timing (VVT) system?

Accepted Answer

Optimize cam phasing for power and efficiency across the RPM range

Answer

VVT advances or retards camshaft timing relative to crankshaft position to balance low-end torque with high-RPM power output.

Question 5

A long-term fuel trim (LTFT) reading of +18% on Bank 1 most likely indicates what condition?

Accepted Answer

Lean condition on Bank 1 requiring added fuel

Answer

A high positive LTFT value shows the ECU is adding significant fuel to compensate for a lean condition, such as a vacuum leak or weak injector.

(CPT) Certified Process Technician Practice Test

(CPT) Certified Process Technician Practice Test

CPT Engine Performance & Tuning 2