What is the cause of low fuel transfer pump pressure?

• A. Plugged fuel filter.
• B. Return line restriction.
• C. Leaking fuel tank vent.
• D. Regulating valve stuck closed.

Answer: (A)

A plugged fuel filter blocks the path fuel must take to reach the pump, creating a large restriction on the suction side. The pump has to pull fuel through that blockage, which lowers the flow available to it and reduces the pressure it can deliver downstream. In practice, this shows up as low fuel pressure in the system. The other possibilities either don’t directly create a suction restriction (a restricted return line alters flow differently and can raise or redistribute pressure, not typically cause a drop at the transfer pump), affect venting rather than pump pressure, or would only cause low pressure if the regulator were stuck closed—whereas a clogged filter is the most direct, common cause of low transfer pump pressure.