Engine Test

What is the maximum percentage of cylinder leakage allowed by most auto manufacturers?

20%

Engine mechanical testing should be performed in all of the following situations, EXCEPT:

before performing major engine repair.

What unit of measure can be used when testing engine compression and cylinder leakage?

Pounds per square inch (psi) or kilopascals (kPa)

Which of the following methods may be used to manually perform a cylinder power balance test?

Unplug individual fuel injectors

An engine has one cylinder that measured substantially lower than specifications on a compression test. Technician A says a cylinder leakage test should be performed only on the cylinder with low compression pressure. Technician B says a cylinder leakage test should be performed on all cylinders. Who is correct?

Technician A

During a running compression test, a cylinder rises to about 80% of the cranking compression pressure when the throttle is snapped to wide open. Technician A says this may indicate a worn camshaft lobe. Technician B says this may indicate excessive carbon buildup. Who is correct?

Technician A

Technician A says that a light ticking noise while the engine is idling could be a valve lifter problem. Technician B says a vibration that occurs only on moderate acceleration is likely caused by worn crankshaft bearings. Who is correct?

Technician A

Technician A says when performing a power balance test, it is important to reactivate the disabled cylinder and allow the engine to run for at least 10 seconds to stabilize before disabling the next cylinder. Technician B says when performing a power balance test, you must shut down and restart the engine after disabling each cylinder. Who is correct?

Technician A

A running compression test is performed on each cylinder in two parts. Technician A says after removing the spark plug and grounding the plug wire, the first part is to install the gauge, start the engine and snap the throttle open and record the reading on each cylinder. Technician B says after removing the plug and grounding the wire, the first part is to install the gauge, start the engine and press and release the bleed valve and record the stabilized reading in each cylinder. Who is correct?

Technician B

A vehicle has black smoke coming from the exhaust after the engine is warmed up. Technician A says this may indicate worn valve springs. Technician B says this may indicate an excessively rich fuel mixture. Who is correct?

Technician B

Technician A says that if an engine is losing oil but no leak source is found after a visual inspection, the technician should overfill the crankcase by adding two extra quarts and force the leak to get larger. Technician B says the technician should add a fluorescent dye to the engine oil and operate the engine while using a black light to find the leak. Who is correct?

Technician B

Technicians A and B are discussing cylinder leakage test results. Technician A says that 5% leakage past the exhaust valves is acceptable. Technician B says that all piston rings will leak at least 20%. Who is correct?

Neither Technician A nor Technician B

Which of the following malfunctions is indicated by a running compression reading that rises to 95% of cranking compression pressure when the throttle is snapped to wide open?

Restriction in the exhaust system

On an engine with a separate fuel injector for each cylinder, cylinder power balance tests may involve:

disconnecting the fuel injector wire connection at each individual injector one at a time.

When testing intake manifold vacuum, a low steady reading at idle is likely to be caused by

late ignition timing or valve timing.

When testing intake manifold vacuum, a low steady reading at idle is likely to be caused by:

late ignition timing or valve timing.

Which of the following malfunctions would be more likely to be revealed during a running compression test than a cranking compression test?

A badly worn camshaft lobe

Which of the following is one of the first steps a technician should take when a customer reports excessive oil consumption?

Find out the oil consumption allowance specified by the manufacturer.

When the throttle is snapped wide open during a running compression test, what reading should be seen for a normal cylinder?

About 80% of the cranking compression pressure

An engine's vacuum is being tested with a gauge. When the throttle is snapped wide open momentarily, the gauge drops to zero and then reaches a high of 20 inches. Technician A says this could indicate worn piston rings. Technician B says the reading should have reached about 27 inches. Who is correct?

Both Technician A and Technician B

Technicians A and B are discussing how to obtain the most accurate results when testing cranking compression on a gasoline engine. Technician A says the battery must be fully charged. Technician B says at least five compression pulses should be made on each cylinder while watching the gauge. Who is correct?

Both Technician A and Technician B

When diagnosing engine noise, Technician A says a mechanical stethoscope may not be appropriate in pinpointing a squeaking drive belt. Technician B says a whirring noise is likely to be from external accessories such as alternators, water pumps and belt tensioners. Who is correct?

Both Technician A and Technician B

A running compression test indicates a possible restriction on the intake side of a cylinder. What should the technician do next?

Inspect the suspect components.

When performing vacuum testing, Technician A says the vacuum reading at idle will be higher on an engine with a high-performance camshaft than a normal engine. Technician B says that the gauge readings for a normal engine will be higher at high altitudes than at sea level. Who is correct?

Neither Technician A nor Technician B

When testing relative compression using a lab scope and ammeter, Technician A says the current draw peaks (spikes) should be nearly equal. Technician B says the engine should be operating at idle for any lab scope test. Who is correct?

Neither Technician A nor Technician B

When performing a cranking sound diagnosis, Technician A says that all engines may be prevented from starting by holding the throttle wide open while cranking. Technician B says that an engine may be disabled by removing the fuel pump fuse or relay (if equipped). Who is correct?

Technician B

When testing intake manifold vacuum, the gauge reads normal at idle, but reads very low when the engine is held steady at 2,500 rpm. Technician A says this indicates worn valve guides. Technician B says this indicates a restricted exhaust system. Who is correct?

Technician B

Which of the following can be measured by a running compression test, but NOT by a cranking compression test?

The ability of the engine to breathe

When checking cranking compression, which of the following malfunctions is either confirmed or ruled out by performing a wet test on a cylinder with low compression?

Worn piston rings

When testing intake manifold vacuum, the gauge needle oscillates back and forth rapidly, which generally indicates:

a mechanical condition such as a burned or bent valve.

When performing a cylinder leakage test, the gauge reads 7% leakage and air leakage can be heard at the oil fill hole with the cap removed. This indicates:

a normal amount of leakage past the piston rings