ASE4 General Engine Diagnosis

Question 1

A customer complains of a rough idle that disappears at higher RPMs. Which tool is BEST used to identify a misfiring cylinder?

Accepted Answer

Scan tool with misfire counters

Answer

A scan tool displaying misfire counters can identify which specific cylinder is misfiring under live conditions.

Question 2

A cylinder power balance test shows that shorting cylinder #3 causes no RPM drop. This indicates:

Accepted Answer

That cylinder is not contributing to engine power

Answer

No RPM drop when a cylinder is disabled means that cylinder was already not contributing power, indicating a fault.

Question 3

Low compression on two adjacent cylinders most likely indicates:

Accepted Answer

A blown head gasket between those cylinders

Answer

A blown head gasket between two adjacent cylinders allows compression to leak between them, causing both to read low.

Question 4

When performing a cylinder leakage test, air is heard escaping from the throttle body. This indicates:

Accepted Answer

A leaking intake valve

Answer

Air escaping back through the throttle body during a leak-down test indicates a leaking intake valve on that cylinder.

Question 5

An engine has good compression but produces blue smoke at startup that clears after a few minutes. The MOST likely cause is:

Accepted Answer

Leaking valve stem seals

Answer

Valve stem seals allow oil to seep into the combustion chamber when the engine sits, burning off as blue smoke at startup.

ASE4 - ASE Automobile Engine Performance Practice Test