Check the STC plumbing.

NOTE: Make sure the STC oil supply line is plumbed between the STC valve oil outlet fitting and the STC rocker housing connection.

Check for a collapsed or restricted oil supply line from the STC valve to the STC rocker housing connection.

Check the STC valve calibration. Refer to Procedure 006-037 in Section 6.

Remove the shutoff valve from the STC rocker housing connecting.

Install a shop air line regulator, Part Number ST-990-40, and a 0-1109 kPa [0-160 psi] pressure gauge, Part Number 3375275, to the STC rocker housing connection.

Remove the rocker lever cover assembly. Refer to Procedure 003-011 in Section 3.

Apply 278 kPa [40 psi] air pressure to the STC oil manifold to push oil out of the lines.

Lower the pressure to 69 kPa [10 psi].

Air will leak around each injector link.

If the air leakage around a link is excessive, check the injector overhead adjustment. Refer to Procedure 003-004 in Section 3.

If air does not leak around each injector tappet link, remove the injector. Refer to Procedure 006-026 in Section 6.

Once the injector is removed, air must leak at the STC oil supply tube.

If air does not leak at the oil supply tube, check the oil transfer tube and oil supply tube for restriction at the problem cylinder.

Listen for large air leaks at joints between the STC oil manifold and transfer tubes, or transfer tubes and injectors. This will indicate a missing or cut o-ring, or leaking oil plumbing.

Replace the damaged part(s).

Remove the pressure gauge, tee fitting, and shutoff valve from the STC rocker housing connection.

Connect the oil supply line to the STC rocker housing connection.