Compression & cylinder leakage

Multiple Choice

Why is it important to carry out a compression test on petrol engines?

• To check the engine's fuel efficiency

• To diagnose potential engine faults

• To measure oil levels

• To test the battery strength

Multiple Choice

Which of the following is NOT a reason to carry out a compression test on an engine?

• To confirm or eliminate worn piston rings or cylinder bore

• To check for worn valve gear or camshaft

• To diagnose a faulty ignition circuit

• To get an idea of the engine's internal condition in a used car

Multiple Select

According to the slides, which of the following are valid reasons to incorporate a compression test into your normal service routine?

• To get an early indication of internal engine wear

• To check the pressure produced by modified engine parts

• To avoid changing the fuel filter

• To detect a blown head gasket before it becomes a cracked cylinder head

Fill in the Blanks

To calculate the maximum pressure in psi, multiply the compression ratio by

.

Multiple Choice

If the compression ratio of an engine is 10.8:1, what is the maximum pressure in Bar according to the formula provided?

• 108 psi

• 14.9 kPa

• 15 Bar

• 220 psi

Multiple Choice

Which of the following steps are necessary to protect the ignition circuit during preparation?

• Disconnect the ignition module wiring plug or LT lead

• Move the LT lead clear of the connector

• Leave the ignition circuit connected

• Ensure the circuit remains isolated

Multiple Choice

What can wet oily spark plugs indicate during preparation?

• Worn piston rings or cylinder bores

• Good engine condition

• Excessive air intake

• Faulty ignition circuit

Multiple Choice

What is the purpose of fully depressing the accelerator pedal during the compression test?

• To allow for maximum air intake

• To increase fuel flow

• To reduce engine speed

• To isolate the ignition circuit

Multiple Choice

Which of the following is a sign of a good compression test result according to the slides?

• Quick build up of pressure with 66% by the second revolution and 80% by the fourth revolution

• Slow build up of pressure with less than 66% by the second revolution

• Maximum pressure variance of more than 20% across cylinders

• Presence of coolant in the oil

Fill in the Blanks

The pressure readings during a compression test should be noted on the second, fourth, and

revolution.

Multiple Choice

If adjacent cylinders show low pressure with greater than a 10% variance, what could this indicate?

• Internally cracked cylinder head or blown head gasket between those cylinders

• Worn piston rings

• Excessive carbon build up

• Normal engine operation

Fill in the Blanks

A wet compression test is carried out by pouring

of engine oil down each spark plug hole before testing.

Multiple Select

Which of the following are possible causes if there is no increase in pressure during a wet compression test?

• Pitted or worn valve/valve seat

• Externally cracked cylinder head

• Burnt valve

• Worn camshaft lobe

Multiple Select

Which of the following are possible causes of air loss detected during a cylinder leakdown test?

• Faulty inlet valve

• Faulty exhaust valve

• Cracked cylinder head

• Worn piston rings

Multiple Choice

Which of the following faults is indicated if bubbles are observed in the coolant during a cylinder leakdown test?

• Worn piston rings

• Faulty inlet valve

• Head gasket failure or crack in block/head

• Faulty exhaust valve

Multiple Choice

Which of the following is a symptom of low compression in a petrol engine?

• Engine misfires

• High fuel efficiency

• Smooth engine operation

• Rapid acceleration