CPT Engine Performance & Tuning 3

Question 1

Which ignition timing condition is most likely to cause engine knock (detonation) under load?

Accepted Answer

Timing too far advanced

Answer

Overly advanced ignition timing causes the air-fuel mixture to ignite too early, resulting in abnormal combustion pressure that causes knock.

Question 2

A technician finds a crankshaft position sensor signal that drops out at operating temperature. The most likely cause is:

Accepted Answer

Heat-related sensor or wiring failure

Answer

Intermittent signal loss that only occurs at operating temperature is a classic symptom of a heat-sensitive sensor or wiring insulation failure.

Question 3

What parameter does the mass airflow (MAF) sensor measure to help the ECU calculate fuel delivery?

Accepted Answer

Air density and volume flow rate

Answer

The MAF sensor measures the actual mass of air entering the engine per unit time, which the ECU uses as the primary input for fuel injection pulse width.

Question 4

When performing a compression test, a cylinder reading significantly lower than the others that improves greatly with a wet test (adding oil) suggests:

Accepted Answer

Worn or stuck piston rings

Answer

Oil temporarily seals worn ring gaps, so a compression increase on the wet test points to ring or cylinder wall wear rather than a valve problem.

Question 5

A faulty coolant temperature sensor (CTS) stuck at a cold reading will cause the ECU to:

Accepted Answer

Continuously enrich the fuel mixture as if at cold start

Answer

The ECU interprets the cold reading as a perpetual cold-start condition and adds extra fuel enrichment, causing a persistent rich running condition.

(CPT) Certified Process Technician Practice Test

(CPT) Certified Process Technician Practice Test

CPT Engine Performance & Tuning 3