Engine Testing & Diagnostics Flashcards
7 cards from real ACS practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Engine Testing & Diagnostics flashcards as text
When checking ignition timing using a timing light on a running engine, the light should flash at what point relative to the crankshaft?
Answer: At the specified degrees before TDC
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.
A turbocharged engine's manifold pressure continues to rise after the throttle is advanced to a set position. What component has likely failed?
Answer: Wastegate controller
A failed wastegate that sticks closed prevents exhaust from bypassing the turbine, causing uncontrolled manifold pressure rise (overboosting).
Fuel flow is within normal limits but EGT is abnormally high on one cylinder. What is the most likely cause?
Answer: Clogged fuel injector on that cylinder
A clogged fuel injector delivers insufficient fuel to one cylinder, creating a lean mixture that raises EGT on that cylinder.
What is the primary purpose of performing a cold cylinder check during engine diagnostics?
Answer: To identify cylinders not firing or producing power
A cold cylinder check identifies cylinders that are not contributing power, indicating ignition failure, fuel starvation, or mechanical issues.
An engine oil analysis report shows elevated iron and chrome levels. What engine components are most likely experiencing abnormal wear?
Answer: Piston rings and cylinder walls
Chrome (from chrome-plated rings) and iron (from cylinder walls) appearing together in oil analysis are classic indicators of ring and cylinder bore wear.
During engine run-up, the prop governor check is performed by increasing RPM and pulling the prop control back. What should happen to RPM?
Answer: RPM should drop and stabilize at a lower value
Pulling the prop control back commands a lower RPM setting; the governor responds by coarsening the blade pitch, reducing RPM to the selected value.
What reading on a differential compression tester indicates a cylinder is in acceptable condition?
Answer: Less than 25 psi differential between reference and cylinder pressure
FAA guidance generally accepts cylinders with no more than a 25% (about 20 psi on an 80 psi tester) differential pressure drop as serviceable.