Oil Pressure Test
Ensure that the engine oil pressure is within the correct operating range before you perform 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 the Testing and Adjusting, "Engine Oil Pressure - Test" topic for more information.
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. |
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| Tools Needed | ||
| Part Number | Part Name | Quantity |
| 149-6111 | Oil Pressure Test Kit | 1 |
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| Illustration 1 | g00527135 |
(1) Pressure gauge (2) O-ring seals for the solenoid valve (3) Adapter (4) Test body for the control valve (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" for more information.
- Insert the adapter assembly into bore (7) for the control valve. Hold the assembly approximately 3.18 mm (.125 inch) above the bottom of the bore in order to allow the oil to enter the adapter.
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| Illustration 2 | g00521294 |
Typical example (7) Bore | |
- Start the engine. Ensure that the compression brake switch is in the OFF position.
- 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.
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| Illustration 3 | g00521295 |
Typical example (8) Solenoid armature | |
- 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" for more information.
The oil pressure readings above 1000 rpm should be 380 ± 205 kPa (55 ± 30 psi).
If the oil pressure readings are too low, proceed to Testing and Adjusting, "Solenoid Valve (Compression Brake) - Test".
If the oil pressure readings are too high in the compression brake housings, the engine oil pressure is too high. Refer to the Testing and Adjusting, "Engine Oil Pressure - Test" topic for more information.