TECH DOWNLOAD : Compression Test

By: APR | 03/31/2015 < Back to Blog Home

A compression test is a dynamic type procedure that can tell you the overall health of an engines mechanical components.

STEP 1. With a warm engine, remove all four ignition coils and spark plugs. Lift up the rear seat cushion and disconnect the electrical connection to the low pressure fuel pump.

STEP 2. Connect a battery charger. This will keep the vehicles electrical system at a constant voltage during the cranking portion of the test.

STEP 3. Prior to installing your compression tester, verify that the gauge is reading zero and the hose you are about to install contains a one way schrader valve.

STEP 4. Install the hose into the number one cylinder spark plug hole and connect the gauge. Face the gauge towards the person that will be cranking the engine over. Prior to cranking, insure that the crankshaft area is free of tools, hoses etc.

STEP 5. Crank the engine over until the needle on the gauge face stops moving. The goal here is see what the highest amount of compression the cylinder can acheive. Do not worry about counting the amount of revolutions or how long its taking for the needle to stop moving.

STEP 6. Record and compare all of your data from each of your cylinders with the manufactures specifications pertaining to your specific engine code. Note the wear limit and acceptable variance between cylinders.

If one or more cylinders deviate from the manufactures specifications a mechanical malfunction may be present. A leak down test should be performed to diagnose specific components such as valves, rings, head gasket etc.

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