Engine Diagnostics Flashcards
7 cards from real ASE 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 Diagnostics flashcards as text
Oil pressure is normal on a cold engine but drops very low at warm idle. What is the most likely cause?
Answer: Worn crankshaft main and rod bearings
Excessive bearing clearance lets thin, hot oil escape, lowering pressure at idle.
A deep knock is loudest under load and goes away when the spark plug wire on one cylinder is disconnected. What is the likely cause?
Answer: Worn connecting rod bearing
Rod bearing knock lessens or stops when that cylinder's combustion load is removed.
A vehicle puffs blue smoke for a few seconds at startup after sitting overnight, then clears. What is the most likely cause?
Answer: Worn valve stem seals
Oil seeps past worn valve seals into the cylinders while the engine sits, then burns off at startup.
Which test confirms that combustion gases are entering the cooling system?
Answer: Chemical block test (combustion leak tester)
The block test fluid changes color when exposed to exhaust gases in the coolant.
A light ticking noise occurs at half crankshaft speed. Which component is most likely the source?
Answer: Valvetrain component such as a lifter
Valvetrain parts run at camshaft speed, which is half the crankshaft speed.
An engine gives off heavy black exhaust smoke. What does this usually indicate?
Answer: Rich air-fuel mixture
Black smoke is carbon from unburned fuel caused by a rich mixture.
The engine oil looks milky and light brown on the dipstick. What is the most likely cause?
Answer: Coolant leaking into the oil
Coolant mixing with oil produces a milky, light brown appearance, often from a head or intake gasket failure.