When should a fuel pump be replaced for the PA-28 and PA-44?

The correct choice indicates that a fuel pump for the PA-28 and PA-44 should be replaced when it operates outside the range of 0.5 to 8 psi. This range is critical for ensuring proper fuel delivery and pressure, which are essential for the engine's efficient operation. Maintaining fuel pressure within this specified range is vital, as deviations can lead to insufficient fuel flow or excessive pressure, both of which can adversely affect engine performance and safety.

Operating outside of this range suggests that the fuel pump is not functioning effectively, which could compromise the fuel system's reliability. Thus, replacing the fuel pump once it shows operation outside these parameters ensures optimal performance and safety of the aircraft.