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Diagnostic Testing
/ Test Compression
How to Test Engine Compression
An engine depends on an equal compression reading in each cylinder to run smoothly.
If poor compression
exits in one or more cylinders it can cause a rough idle condition and low power. A compression test
can be performed to check wear or internal damage. To start a engine compression test gauge
is needed. There are two types of gauge
styles, one threads into the spark plug hole which is more accurate.
The other style of gauge is constructed with a rubber plug that is meant to be
pressed against the spark plug hole, this style of gauge is difficult to use. To perform a engine cylinder compression test follow the steps below.
- Remove ignition coil connector or ignition system fuse to disable power
to the ignition system
-
Test ignition system to ensure that the power to the system has been disabled
- Remove #1 cylinder spark plug and insert compression gauge, most gauges
have a hose attachment that is installed into the spark plug hole with the gauge
connecting to the gauge hose.
Engine Cylinder Compression Gauge
- After the compression gauge has been inserted, use the starter to crank
the engine over for about five seconds. Use about the same five seconds to test
the remaining cylinders.
- Record the compression reading as each cylinder is tested
- Remove the compression gauge and reinsert the spark plug
- Follow this procedure until all cylinders have been tested
- Compare cylinders compression reading, all readings should be within about
5% of each other
If low compression exists a cylinder malfunction exits and further inspection
is required. Possible causes for a low compression condition are: burned intake
or exhaust valve, broken piston or piston ring, broken valve spring or a blown
head gasket.
Diagnostic Testing /
Test Compression
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