Before disconnecting any fuel line it is recommended to apply a thin shop rag over it where the fuel pressure has been relieved so as to soak up any fuel that might trickle during servicing. There is a inertia switch which is an electrical device that is situated in the circuit of fuel pump, and in case the fuel pump is not receiving the correct voltage, then the inertial switch should be tested to see if it works as it should. Fuel pump relay has primary and secondary voltage circuits, where the primary circuit controlled by PCM and secondary circuits have a connection with battery voltage through ignition switch. When the ignition switch is ON, the PCM grounds the relay for one second, and during cranking, the PCM grounds the relay as long as it receives a reference signal from the ignition system; otherwise, the fuel pump will be 'off' for two or three seconds, after getting 'on'. In case one feels that his engine is under-fueled, its beneficial to examine battery charge, fuel pump fuse, fuel filter for clogs, fuel lines for leakage. To check fuel pump functioning set the gear selector to PARK/NEUTRAL, apply the parking brake and requesting an assistant to turn the ignition ON while you listen for a short whirring sound. If there is no sound check the ignition fuse and fuel pump relay, which can be situated in the engine compartment fuse center or it can be situated behind the radio in the instrument panel according to the model you are driving. If the relays are good but the pump does not run check the fuel pump circuit and change the fuel pump if required. For models from year 2005 and above, if the fuel pump driver module is assumed to have a problem, take the system for diagnosis. To perform a fuel pressure test, one needs a high fuel pressure gauge and about fittings as shown below.Fig. 2.11 Fittings used in fuel pressure test. When the fuel system pressure is released, connect the gauge to the test port and check for the vacuum while the engine is running at the fuel pressure regulator. All accessory should be turned off and with the ignition turned to ON position read the gauge; in the event of low pressure a shut off valve should be fitted in the fuel return line and the test repeated. This regulator must not be boosted with excessive fuel pressure which should not be more than 85 psi. If it is still low after carrying out checks on restrictions such as a blocked fuel filter, fuel pump will have to be removed for examination. If the recorded pressure is over the limit stated, restrict the fuel return line and replace the fuel pressure regulator. Start the engine and let it idle and with the shut-off valve removed the fuel pressure should be 5 to 10 psi less than the previous reading. If it isn't, ensure there is pull vacuum on fuel pressure regulator vacuum hose, check for restriction or break and replace the regulator if it fails to reduce the pressure when vacuum is applied.
Posted by FordPartsGiant Specialist 
