Cummins N14 STC, Celect, Celect Plus – Service Manual 006-045   STC Oil Delivery System Diagnostics

The following procedure outlines the proper method which must be used to test the STC oil delivery system.

NOTE: Because the oil pressure can be less than 103 kPa [15 psi] when the coolant temperature is above 49°C [120°F], these tests must be performed at temperatures below this level.

Remove the STC oil outlet line (1) from the engine.

Install a flexible hose (2) to the STC valve oil outlet fitting.

Use a tee fitting (3) to install a 1/8-inch male quick connect (4), Part Number 3377244, to the oil supply line (2).

Install a 3/8-inch shutoff valve (5) to the tee fitting. Connect the opposite end of the 3/8-inch shutoff valve to the rocker housing fitting (6).

NOTE: The tee fitting and shutoff valve must be installed as illustrated to conduct the test correctly.

Install a 1/8-inch male quick connect, Part Number 3377244, to the main oil rifle.

Operate the engine and check for leaks.

Install a 0-690 kPa [0-100 psi] pressure gauge, Part Number 3375388, to the quick connect fitting at the STC oil manifold connection.

NOTE: Use one pressure gauge to make all of the pressure checks in this procedure. This will help to eliminate gauge to gauge error when measuring the pressure differential from the oil rifle to the STC oil manifold.

Operate the engine and let it idle.

NOTE: All pressures taken must be taken at idle and while the coolant temperature is below 49°C [120°F].

Close the 3/8-inch shutoff valve at the STC oil manifold. Record the pressure (P1).

Open the 3/8-inch shutoff valve at the STC oil manifold. Record the pressure (P2).

Move the pressure gauge to the quick connect fitting at the main oil rifle and record the pressure (P3).

P3 must be at least 100 kPa [15 psi] when the engine coolant temperature is below 49°C [120°F]. If not, the main oil rifle pressure is inadequate. Reference the Lubricating Oil Pressure Low troubleshooting symptom tree in Section TS.

If P1 is less than 100 kPa [15 psi], and P3 is at least 100 kPa [15 psi], a complete blockage exists between the oil rifle and the STC rocker housing connection. Check for blockage. Refer to Procedure 006-046 in Section 6.

If P1 is greater than or equal to 100 kPa [15 psi], and if P1 minus P2 is greater than 35 kPa [5 psi], partial blockage exists between the oil rifle and the STC rocker housing connector or leakage exists between the oil rifle and the STC rocker housing connection, or leakage exists between the STC rocker housing connection and injector(s).

Check for partial blockage or leakage in the system. Refer to Procedure 006-046 in Section 6.

If P1 is greater than or equal to 100 kPa [15 psi], and if P1 minus P2 is less than or equal to 35 kPa [5 psi], no problems exist between the oil rifle and the STC rocker housing connection. A possible leak or blockage exists between the STC rocker housing connection and injector(s).

Check for blockage or leakage between the STC oil manifold and injector(s).