ACS Engine Testing & Diagnostics 3

Question 1

When checking ignition timing using a timing light on a running engine, the light should flash at what point relative to the crankshaft?

Accepted Answer

At the specified degrees before TDC

Answer

Ignition timing is set to fire the spark plug at a specified number of degrees before TDC to allow the fuel-air mixture to reach peak pressure at the optimal piston position.

Question 2

A turbocharged engine's manifold pressure continues to rise after the throttle is advanced to a set position. What component has likely failed?

Accepted Answer

Wastegate controller

Answer

A failed wastegate that sticks closed prevents exhaust from bypassing the turbine, causing uncontrolled manifold pressure rise (overboosting).

Question 3

Fuel flow is within normal limits but EGT is abnormally high on one cylinder. What is the most likely cause?

Accepted Answer

Clogged fuel injector on that cylinder

Answer

A clogged fuel injector delivers insufficient fuel to one cylinder, creating a lean mixture that raises EGT on that cylinder.

Question 4

What is the primary purpose of performing a cold cylinder check during engine diagnostics?

Accepted Answer

To identify cylinders not firing or producing power

Answer

A cold cylinder check identifies cylinders that are not contributing power, indicating ignition failure, fuel starvation, or mechanical issues.

Question 5

An engine oil analysis report shows elevated iron and chrome levels. What engine components are most likely experiencing abnormal wear?

Accepted Answer

Piston rings and cylinder walls

Answer

Chrome (from chrome-plated rings) and iron (from cylinder walls) appearing together in oil analysis are classic indicators of ring and cylinder bore wear.

(ACS) Airman Certification Standard Certified Mechanic Practice Test

(ACS) Airman Certification Standard Certified Mechanic Practice Test

ACS Engine Testing & Diagnostics 3