Fuel pump / fuel pressure — check
Fuel pump operation check
1. Sit inside the vehicle with the windows closed, turn the ignition key to ON (not START) and listen carefully for the sound made by the fuel pump as it’s briefly turned on by the PCM to pressurize the fuel system prior to starting the engine. You will only hear a whirring sound for a second or two, but that sound tells you that the pump is working. If you can’t hear the pump, remove the fuel filler cap, then have an assistant turn the ignition switch to ON while you listen for the sound of the pump operating for a couple of seconds.
2. If the pump does not come on when the ignition key is turned to ON, check the fuel pump fuse (s) and relay (see illustration 2.2). If the fuse(s) and relay are okay, check the wiring back to the fuel pump. If the fuse, relay and wiring are okay, the fuel pump is probably defective. If the pump runs continuously with the ignition key in its ON position, the Powertrain Control Module (PCM) is probably defective. Have the PCM checked by a dealer service department or other qualified repair shop.
Fuel pressure check
Warning: The fuel delivery system is made up of a low-pressure system and a high-pressure system. The following procedure only measures the fuel pressure in the low-pressure fuel system (in-tank fuel pump). The high-pressure fuel system operates at extremely high pressures and can cause injury. Only a qualified service center should perform diagnostics on the high-pressure fuel system.
Connecting a fuel pressure gauge — non-6.0L models
3. Relieve the fuel pressure (see Fuel pressure relief procedure).
4. Disconnect the quick connect fitting (see Fuel lines and fittings — general information and disconnection) for the fuel feed hose from the fuel feed pipe at the rear of the driver’s side cylinder head (see illustration). Use a shop towel in order to catch any fuel that may leak.
4.4 Disconnect the fuel seed hose from the fuel seed pipe, and using the proper fittings, connect a fuel pressure gauge (V6 models shown, V8 models similar)
5. Install a fuel pressure gauge test adapter between the fuel feed pipe and the fuel feed hose. Connect the gauge to the adapter.
6. Cycle the ignition to run the fuel pump, and check for leaks prior to performing the fuel pressure check.
Connecting a fuel pressure gauge — 6.0L models
7. To measure the fuel pressure, you’ll need a fuel pressure gauge, and a hose and fitting suitable for connecting the gauge to the Schrader valve-type test port on the fuel feed line (see illustration).
4.7 A typical fuel pressure gauge set up
A Screw-on adapter for the Schrader valve on the fuel rail
B Hose with fitting to connect to the adapter
C Bleeder valve (optional)
D Bleeder hose (optional)
8. Locate the fuel pressure test port, unscrew the cap and connect a fuel pressure gauge (see illustrations).
4.8a The fuel pressure test port on V8 models is located on the right fuel rail
4.8b The fuel pressure gauge connected to the test port on the fuel rail (V8 model shown)
9. Cycle the ignition to run the fuel pump, and check for leaks prior to performing the fuel pressure check.
Fuel pressure check
10. Start the engine and allow it to idle. Note the gauge reading as soon as the pressure stabilizes, and compare it with the pressure listed in this Chapter’s Specifications.
a) If the pressure is lower than specified, suspect a restricted fuel filter (the fuel filter is an integral part of the fuel pump/ fuel level sensor module; to replace it you must replace the fuel pump). Also check the fuel lines and hoses for kinks, blockages and leaks.
b) Except 6.0L models: If there are no restrictions and you changed the fuel filter but the pressure is still lower than specified, the regulator (which is an integral component of the fuel pump module) might be stuck in the open position, which will prevent the fuel system from reaching its normal operating pressure range. The regulator is not serviceable separately; if it’s defective you must replace the fuel pump module.
c) It’s possible that one or more of the fuel injectors might be leaking or stuck open (but if this is happening the engine will be running very poorly and will most likely have set a trouble code). Remove and inspect the injectors (see Fuel rail and injectors — removal and installation).
d) Except 6.0L models: If the fuel pressure is higher than specified, the fuel pressure regulator might be stuck in the closed position. The regulator is an integral component of the fuel pump module, and is not serviceable separately; if it’s defective, you must replace the fuel pump module.
11. Drive the vehicle and monitor fuel pressure. If fuel pressure dramatically decreases at cruise speed, during acceleration or hard cornering maneuvers, check for a restricted fuel filter (the fuel filter is an integral part of the fuel pump/fuel level sensor module; to replace it you must replace the fuel pump). Also check the fuel lines and hoses for kinks, blockages and leaks.
12. Turn off the engine. Verify that the fuel pressure loses no more than the specified pressure for one minute after the engine is turned off.
Tip: If pressure leaks down too quickly, check for a leaky check valve in the fuel pump by pinching off the line to the fuel tank and retesting. If pressure still drops, check for a leaking fuel injector.
Tip: If pressure holds, the check valve in the fuel pump may be at fault, requiring fuel pump replacement.
13. On 6.0L models, disconnect the fuel pressure gauge and screw on the test port cap. On all models except 6.0L, remove the fuel pressure gauge and adapter and reconnect the fuel line fitting. Clean up any spilled gasoline.
14. Start the engine and verify that there are no fuel leaks.