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 Solenoid 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 | |
- Attach pressure gauge (1) to solenoid valve adapter (6).
- Remove the solenoid valve and the three seals from the compression brake housing. Refer to Disassembly and Assembly, "Compression Brake - Disassemble".
- Install three seals (2), which are included in the 149-6111 Oil Pressure Test Kit. Place the smallest seal in the bottom of the bore for the solenoid. Install the other two seals on solenoid valve adapter (6).
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Illustration 2 g00514470 - Lubricate the seals with clean engine oil and install the adapter assembly in bore (7) for the solenoid valve. Hand tighten the adapter assembly and then tighten the adapter assembly for an additional 1/4 turn.
- Start the engine. Ensure that the switch for the compression brake is in the OFF position.
- Record the oil pressure reading.
- Increase the engine speed by 400 rpm.
- Repeat Steps 6 and 7 up to the rated engine rpm.
- Stop the engine. Install the solenoid valve. Refer to Disassembly and Assembly, "Compression Brake - Assemble".
Compare the oil pressure readings from the solenoid valve to the oil pressure readings from the Testing and Adjusting, "Control Valve (Compression Brake) - Test".
- If the oil pressure at the solenoid valve is higher than the oil pressure at the control valve, continue with Steps 10 through 15.
- If the oil pressure at the solenoid valve is the same pressure as the oil pressure at the control valve, the oil pressure to the compression brake is too low. Refer to Testing and Adjusting, "Engine Oil Pressure - Test".
- Start the engine.
- Disconnect the wires from each solenoid valve except for the solenoid valve that is being tested in order to check each solenoid valve individually.
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Illustration 3 g00514472 - Turn the switch for the compression brake to the ON position. Observe the movement of solenoid armature (8). The solenoid armature should snap down fully. Push down on the solenoid armature in order to verify that the solenoid is fully actuated.
If the solenoid valve fully actuates, proceed to Step 14. Otherwise, continue to Step 13.
- Check the voltage at the terminals on the solenoid valve. There should be at least ten volts at the terminals.
Insufficient voltage at the terminals indicates that there are either poor connections in the circuit or that battery voltage is low. Verify proper battery voltage. Check the condition of the connections and clean the connections.
Replace the solenoid valve if both of the following conditions exist:
- The solenoid valve is receiving the correct voltage.
- The solenoid valve does not actuate fully.
- Look for excessive oil leakage from the bottom of the compression brake housing opposite the solenoid valve. While the solenoid valve is electrically actuated, leakage should be no more than two drops per second. Replace the solenoid valve if there is excessive leakage.
Note: When the solenoid valve is deactivated, oil will dump from the solenoid valve. This is a normal condition that should not be confused with oil leakage while the solenoid valve is electrically actuated.
- Repeat Steps 11 through 14 for each solenoid valve.
