ASE Engine Diagnostics 4

Question 1

Oil pressure is normal on a cold engine but drops very low at warm idle. What is the most likely cause?

Accepted Answer

Worn crankshaft main and rod bearings

Answer

Excessive bearing clearance lets thin, hot oil escape, lowering pressure at idle.

Question 2

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?

Accepted Answer

Worn connecting rod bearing

Answer

Rod bearing knock lessens or stops when that cylinder's combustion load is removed.

Question 3

A vehicle puffs blue smoke for a few seconds at startup after sitting overnight, then clears. What is the most likely cause?

Accepted Answer

Worn valve stem seals

Answer

Oil seeps past worn valve seals into the cylinders while the engine sits, then burns off at startup.

Question 4

Which test confirms that combustion gases are entering the cooling system?

Accepted Answer

Chemical block test (combustion leak tester)

Answer

The block test fluid changes color when exposed to exhaust gases in the coolant.

Question 5

A light ticking noise occurs at half crankshaft speed. Which component is most likely the source?

Accepted Answer

Valvetrain component such as a lifter

Answer

Valvetrain parts run at camshaft speed, which is half the crankshaft speed.

ASE - Automotive Service Excellence Certified Tech Practice Test