How to Test the Fuel Pump System in a MerCruiser

Gasoline-fired Mercruiser engines use both a low-pressure diaphragm-type fuel pump and an electric high-pressure fuel pump. The low-pressure pump supplies the high-pressure pump, the fuel-pressure gauge and the engine's fuel rails. This means that, if the fuel pressure remains normal on the high-pressure side of the system, the low pressure side is supplying it adequately.

Instructions

    • 1

      Open the engine compartment. Pump the fuel primer bulb until it is firm to the touch. Check the fuel lines for leaks.

    • 2

      Turn the key switch to the "On" position. Listen for the fuel pump. Check the fuel pressure gauge to determine if the fuel pressure is within the normal operating range of 40 to 45 psi. Turn the key switch to "Off."

    • 3

      Disconnect the feed hose from the fuel rail. Open the Schraeder shut-off valve on the fuel rail. Turn the key switch to the "On" position.

    • 4

      Close the valve on the Schraeder shut-off valve and watch the fuel pressure for one minute. The fuel pressure should remain constant.

    • 5

      Turn the key switch to "Off." Open the Schraeder valve to relieve all fuel system pressure.