The fault code SPN 1077 FMI 14 typically indicates an issue with the high-pressure fuel system, specifically related to internal or external leakage. This fault is detected by the Motor Control Module (MCM), which monitors the rail pressure during engine shutdown and compares it to a stored learned value. If the bleed-down rate has changed due to leakage and is below the learned value, this code will set.

To troubleshoot this issue, you should:

1. Inspect for external leakage: Check components like the high-pressure pump, fuel lines, fuel rail, and injectors.
2. Perform a Pressure Limiting Valve (PLV) Leakage Test: If the PLV fails, it needs to be replaced.
3. Conduct an Amplifier/Needle Return Flow Test: If this test fails, necessary repairs should be made.