ENGINE PERFORMANCE PRACTICE QUESTIONS (10/15/2026)

Technician A says that the piston should be at BDC (Bottom dead center) when performing a cylinder leakage test. Technician B says that all the spark plugs should be removed before performing a cylinder leakage test.

B Only.

A vehicle has blue smoke from the tailpipe at idle. Which of these could be the cause?

a. Seized oil control rings.

b. Coolant leaking into the cylinder

c. A shorted fuel injector.

d. A leaking vacuum hose.

Seized oil control rings.

A cylinder leakage test is being performed. Cylinder #4 has a 45% leakage reading. During the test, the technician observes air bubbles in the coolant recovery tank. The cause could be a:

a. Leaking intake valve.

b. Burned exhaust valve.

c. Broken piston ring.

d. Leaking head gasket.

Leaking Head Gasket.

White smoke comes from a vehicle’s exhaust. Any of these could be the cause EXCEPT:

a. A leaking cylinder head gasket.

b. A leaking intake valve gasket.

c. A cracked cylinder head.

d. A cracked water pump.

A cracked water pump.

A vehicle has excessive oil consumption and constant blue smoke from the exhaust. This could be caused by:

a. Loose wrist pins.

b. Incorrectly adjusted valves.

c. Worn crankshaft bearings.

d. Worn valve guides.

Worn valve guides.

When a cylinder leakage test is performed, the piston should be at:

a. TDC (Top Dead Center) on the compression stroke.

b. TDC (Top Dead Center) on the exhaust stroke.

c. BDC (Bottom Dead Center) on the exhaust stroke.

d. BDC (Bottom Dead Center) on the intake stroke.

TDC (Top Dead Center) on the compression stroke.

Air is heard coming from the dipstick tube during a cylinder leak-down test. Technician A says that worn compression rings could be the cause. Technician B says that worn valve guides could be the cause. Who is right?

A Only.

When performing an exhaust system back pressure test at the upstream O2 sensor on a 4-cylinder engine, 12psi is measured. Which of these could be the cause?

a. Incorrect valve timing.

b. Restricted catalytic converter.

c. Blown head gasket.

d. Restricted fuel filter.

Restricted catalytic converter

During an engine manifold vacuum test, the vacuum at idle is 16 in. g. After raising the engine speed to 2500 RPM with no load, the vacuum slowly drops to about 9 in. Hg. These results could indicate:

a. A burned valve.

b. A restricted exhaust system.

c. Retarded ignition timing.

d. Normal engine operation.

A restricted exhaust system.

Which of these conditions will result in the HIGHEST intake manifold vacuum of a gasoline engine?

a. An engine running steady at fast idle when cold.

b. An engine running steady at 2500rpm when warm.

c. An engine accelerating during wide open throttle (WOT)

d. An engine decelerating during closed throttle from 3500rpm

An engine decelerating during closed throttle from 3500rpm

A Customer states that the engine idles OK, but it has no power no acceleration. An engine vacuum test indicates 18.5 in. Hg at idle and 12.5 in. Hg at 2000 RPM. Which of these could be the cause?

a. A sticking IAC (Idle Air Control) valve

b. A restricted exhaust system

c. A stuck-open EGR valve

d. A stuck-closed EGR valve

A restricted exhaust system.

A idle, an engine in good mechanical condition should have a vacuum gauge reading at the intake manifold between:

a. 5-9 in. Hg

b. 10-14 in. Hg

c. 17-21 in. Hg

d. 22-30 in. Hg

17-21 in. Hg

An engine has poor performance. A vacuum gauge is connected to intake manifold port. The needle on the gauge fluctuates between 15 in. Hg vacuum at idle. The vacuum gauge reading indicates:

a. A normal condition

b. Late ignition or valve timing

c. A burned exhaust valve

d. A restricted exhaust

A burned exhaust valve

A cylinder power balance test is used to determine:

a. Cylinder horsepower-to-engine displacement.

b. If the harmonic balancer is out of balance.

c. Throttle position for optimum power.

d. Related performance between cylinders.

Related performance between cylinders.

A vehicle has a rough idle and low power on acceleration. The results of a cylinder power balance test are shown. Which of these could be the cause?

a. Low fuel pressure.

b. Electricity open fuel injector coil.

c. Stuck-open EGR valve

d. Failed upstream oxygen sensor

Stuck-open EGR valve

An engine has low compression on all cylinders. Technician A says that incorrect ignition timing could be the cause. Technician B says incorrect camshaft timing could be the cause. Who is right?

B Only.

The pressure readings shown were obtained during a cranking compression test. Which of these could be the cause?

a. Scored bearings

b. Broken piston rings

c. Worn valve guides.

d. Leaking head gasket.

Leaking head gasket.