Mechanics

Compression Test

Step by step repair guide on how to perform an automotive engine cylinder compression test, this article pertains to all internal combustion engines.

Difficulty Scale: 3 of 10

Begin with the vehicle on level ground, engine "OFF" with the parking brake set.

Step 1 - Before a compression test can be begin, the engine must be disabled so it doesn't start. One way to achieve this is to remove the fuel pump or ignition fuse which can be done by referencing the owners manual. Other methods include disconnecting the ignition module or coils.


Removing Fuel Pump Fuse

Step 2 - Identify the cylinder that will be tested, if all cylinders are being tested it should be performed one at a time. (Note: If all cylinders are being tested and two cylinders test low that are next to each other, the head gasket could be blown between the cylinders.)


Test Cylinder

Step 3 - Remove the electrical connector from the ignition coil or spark plug wire.


Remove Electrical Connector

Step 4 - After removing the wiring connector and mounting bolt, grasp the ignition coil and pull upward to remove.


Remove Ignition Coil

Step 5 - Using a spark plug socket, remove the spark plug. (Note: Clean the spark plug hole prior to removal.)


Remove Spark Plug

AUTHOR


Written by
Co-Founder and CEO of 2CarPros.com
35 years in the automotive repair field, ASE Master Technician, Advanced Electrical and Mechanical Theory.


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Article first published (Updated 2015-01-06)