C4.4 Industrial Engine Compression - Test Caterpillar

The cylinder compression test should only be used to compare the cylinders of an engine. If one or more cylinders vary by more than 350 kPa (51 psi), the cylinder and related components may need to be repaired.

A compression test should not be the only method which is used to determine the condition of an engine. Other tests should also be conducted to determine if the adjustment or the replacement of components is required.

Before the performance of the compression test, make sure that the following conditions exist:

• The battery is in good condition.

• The battery is fully charged.

• The starting motor operates correctly.

• The valve lash is correct.

• All glow plugs are removed.

• The ECM is powered.

• The fuel pressure sensor is connected.

• The suction control valve is connected.

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Illustration 1	g01925436
Typical example

1. Remove the glow plug (1). Refer to Disassembly and Assembly, "Glow Plugs - Remove and Install" for the correct procedure.

2. Electrically disconnect the electronic unit injectors. Alternatively, use the electronic service tool to enable the "Injector Disable Override" to disable the electronic unit injectors from activating.

3. Install a suitable gauge for measuring the cylinder compression in the hole for the glow plug.

4. Remove the fuse for the glow plugs or disconnect the glow plug positive solenoid.

5. Operate the starting motor to turn the engine. Record the maximum pressure which is indicated on the compression gauge.

6. Repeat steps 3 and 5 for all cylinders.

7. Electrically connect the electronic unit injectors. Alternatively, use the electronic service tool to disable the "Injector Disable Override" to enable the electronic unit injectors.

8. Install the fuse for the glow plugs or connect the glow plug positive solenoid.