CPT Ignition Systems & Timing

Question 1

What does ignition timing refer to in an internal combustion engine?

Accepted Answer

The moment the spark plug fires relative to piston position

Answer

Ignition timing refers to the precise moment the spark plug fires in relation to piston position, typically expressed in degrees before or after top dead center (TDC).

Question 2

What is the primary purpose of an ignition timing advance mechanism?

Accepted Answer

To allow combustion to complete optimally as engine speed increases

Answer

As engine RPM increases, combustion must begin earlier (advance) so the expanding gases reach peak pressure at the optimal piston position, maximizing power output.

Question 3

Which tool is used to dynamically measure ignition timing on a running engine?

Accepted Answer

Timing light (stroboscope)

Answer

A timing light uses strobe flashes triggered by the ignition signal to freeze the timing mark on the crankshaft pulley, allowing technicians to read dynamic timing while the engine runs.

Question 4

What is engine knock (detonation) in relation to ignition timing?

Accepted Answer

Uncontrolled ignition of the air-fuel mixture before or simultaneously with the spark

Answer

Detonation occurs when the air-fuel mixture auto-ignites due to heat and pressure rather than the spark, creating a sharp pressure wave that produces a knocking sound and can damage engine components.

Question 5

What is the difference between static timing and dynamic timing?

Accepted Answer

Static timing is measured with the engine off; dynamic timing is measured with the engine running

Answer

Static timing is set with the engine off using a reference mark, while dynamic timing is checked with the engine running using a timing light to account for centrifugal and vacuum advance.

CPT - Certified Performance Technician Practice Test

CPT - Certified Performance Technician Practice Test

CPT Ignition Systems & Timing