Mercury F5AZ-9275-A Sender Assembly

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To perform the fuel pressure test, you will need a fuel pressure gauge and adapter set. Before proceeding, relieve the fuel system pressure and lay a shop towel over any fuel connection to absorb residual fuel. Start the preliminary inspection by checking if the fuel system delivers the proper amount of fuel. Listen for a whirring sound at the fuel filler opening when turning the ignition key to the On position. If there's no sound, check the fuel pump fuse, relay, and circuit. Check for battery voltage to the fuel pump relay connector and power relay connector. If there's no voltage, inspect the fuses and wiring circuit. For the operating pressure check, attach the fuel pressure gauge to the test port and activate the fuel pump without starting the engine. Note the fuel pressure and start the engine to measure the pressure while idling. Detach the vacuum hose from the fuel pressure regulator to check for an immediate increase in pressure. If pressure is too high, inspect for obstructions or replace the fuel pressure regulator. If pressure is low, check the fuel filter and hoses, and if needed, replace the fuel pressure regulator or check the fuel pump. For the fuel pump output pressure check (dead-head pressure), use a fuel pressure gauge with a bleeder valve to relieve pressure after the test. Attach the gauge directly to the fuel feed line at the fuel tank and bridge the terminals on the Diagnostic Test connector to activate the fuel pump. Note the pressure reading and compare it after five minutes. If the hold pressure is less than specified, check the fuel line for leaks or replace the fuel pump.

To perform a more accurate check, you can remove the sending unit from the fuel tank and manually operate the float arm to check its resistance.

On 1998 and earlier models, disconnect the electrical connector at the pump. On 1999 and later models, the electrical connector is located in the harness and must be disconnected at the electrical connector away from the tank.

Position the ohmmeter probes into the electrical connector and check the resistance using the 200-ohm scale on the ohmmeter.