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 Blank

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 Blank

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 Blank

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