Engine Compression Testing Basics

What is the definition of compression ratio in an internal combustion engine?

• The ratio of the volume of the cylinder when the piston is at the bottom of its stroke to the volume when the piston is at the top of its stroke.

• The ratio of the pressure in the cylinder during the power stroke to the pressure during the intake stroke.

• The ratio of the engine's displacement to the total volume of the combustion chamber.

• The ratio of the air-fuel mixture to the exhaust gases.

Which tool is primarily used to measure cylinder pressure during a compression test?

• Torque wrench

• Compression gauge

• Vacuum gauge

• Manometer

What is the first step in the engine compression testing procedure?

• Remove the spark plugs.

• Warm up the engine to its normal operating temperature.

• Disconnect the fuel pump and ignition system.

• Insert the compression gauge into the spark plug hole.

How should the throttle be positioned during a compression test?

• Fully closed

• Half open

• Fully open

• Slightly open

What does a significantly lower compression reading in one cylinder compared to others typically indicate?

• A faulty spark plug

• A clogged air filter

• A leaking head gasket

• A malfunctioning fuel injector

If all cylinders show low compression readings, what is a likely cause?

• A single faulty valve

• A broken timing belt

• A worn-out camshaft

• A weak battery

What is a common issue diagnosed by a compression test that involves the piston rings?

• Valve timing issues

• Worn piston rings

• Faulty ignition coil

• Clogged fuel injectors

During a compression test, what does it mean if two adjacent cylinders have low compression?

• The engine is running too rich.

• There is a problem with the ignition system.

• There is likely a blown head gasket between the cylinders.

• The air filter is clogged.

What should be done if a cylinder shows low compression during the initial test?

• Replace the spark plug and retest.

• Perform a wet compression test by adding a small amount of oil to the cylinder and retesting.

• Immediately replace the cylinder head.

• Adjust the throttle position and retest.