This module covers fuel pump module construction and how it relates to diagnosis, with a focus on returnless fuel systems and their unique failure modes.

Topics include:

• How the fuel pump cup and gravity-feed design works, and why it creates cavitation vulnerability
• Vapor lock behavior in returnless systems and how it produces misfire codes
• Why symptoms are often worse at low fuel levels and how that affects your diagnostic approach
• Electronic returnless systems (FPDM-based), including how the PCM controls pump speed via duty cycle commands and how to interpret the fuel pump monitor signal
• Differential fuel rail pressure and why your gauge reading won't match the scanner PID