Ensure that the engine oil pressure is within the correct operating range before performing any tests on the compression brake. Low engine oil pressure can cause weak braking or no braking at all. High engine oil pressure may cause the compression brake not to operate at all. Refer to Testing and Adjusting, "Engine Oil Pressure - Test".
To properly troubleshoot the compression brake, the technician must know the oil pressure reading at the compression brake housings. The oil pressure reading on the oil pressure gauge in the instrument panel does not provide the same information as the oil pressure reading at the compression brake housings.
Low oil pressure in the compression brake housings may cause weak braking or no braking at all. If the oil pressure in the compression brake housings is too high, the compression brake may not operate at all. High oil pressure may also prevent the compression brake from shutting off.
Oil Pressure Test at Control Valve
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Work carefully around an engine that is running. Engine parts that are hot, or parts that are moving, can cause personal injury. |
| Tools Needed | ||
| Part Number | Part Name | Quantity |
| 149-6111 | Oil Pressure Test Kit | 1 |
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| Illustration 1 | g00514378 |
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149-6111 Oil Pressure Test Kit (1) Pressure gauge (2) Seals (3) Control valve removal tool (4) Control valve test body (5) Control valve adapter (6) Solenoid valve adapter | |
- Assemble pressure gauge (1), control valve test body (4), and control valve adapter (5). Hand tighten the adapter assembly.
- While the engine is not running, remove the control valve. Refer to Disassembly and Assembly, "Compression Brake - Disassemble".
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Illustration 2 g00514468 - Insert the adapter assembly into bore (7) for the control valve. Hold the adapter assembly approximately
3.1750 mm (0.125 inch) above the bottom of the bore in order to allow the oil to enter the adapter assembly. - Start the engine. Ensure that the switch for the compression brake is in the OFF position.
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Illustration 3 g00514472 - Hold the adapter assembly in place and depress solenoid armature (8). Record the oil pressure reading.
Note: Hold the solenoid on only long enough to obtain the oil pressure reading. The oil pressure may be too low at idle in order to operate the compression brake. This condition is normal.
- Increase the engine speed by 400 rpm.
- Repeat Steps 5 and 6 up to the rated engine rpm.
- Stop the engine. Install the control valve. Refer to Disassembly and Assembly, "Compression Brake - Assemble".
The oil pressure readings at the control valve above 1000 rpm should be
275 ± 105 kPa (40 ± 15 psi) .- If the oil pressure readings at the control valve are within the specified range, there is not a problem with the oil pressure in the compression brake.
- If the oil pressure readings at the control valve are below the specified range, proceed to Testing and Adjusting, "Solenoid Valve (Compression Brake) - Test".
- If the oil pressure readings at the control valve are above the specified range, the engine oil pressure is too high. Refer to Testing and Adjusting, "Engine Oil Pressure - Test".
