Testing Fuel Pressure In A '99 Mustang V6

Testing the fuel pressure regulator on a 1999 Mustang V6 involves several steps. First, the negative battery terminal should be disconnected. Next, locate the Schrader valve on the fuel rail or fuel line and relieve pressure. Place a rag underneath to catch any fuel spray. Then, remove the vacuum hose from the factory fuel regulator. After that, remove the regulator itself by unscrewing it from the fuel rail and pulling it up. If the stock regulator had no rubber gasket, be sure to discard the supplied gasket when installing the new one. Reattach the vacuum line and negative battery terminal, then start the vehicle to check for leaks. If you have an adjustable fuel regulator, you can adjust the fuel pressure by disconnecting the vacuum hose and adjusting the top screw.

Check the power at the inertia switch in the trunk.

To check the power at the inertia switch in the trunk of your 1999 Mustang V6, you'll need to locate the switch and then test the voltage.

Locating the Inertia Switch

The inertia switch in your Mustang is located in the trunk, behind the lining, near the latch panel for your hatch. You may need to remove the plastic cover on the hatch to access it.

Testing Voltage

Once you've located the inertia switch, you can test the voltage with a multimeter or a voltage tester. With the key in the 'on' position, check the voltage at the DG/Y and Y/W wires. The DG/Y wire is the input, and the Y/W wire is the output towards the fuel pump.

If you're having trouble accessing the wires or determining which is which, you may need to refer to a Ford service manual or wiring diagram for your specific model.

Interpreting Results

If you measure 12 volts at the DG/Y wire, this indicates that the Constant Control Relay Module (CCRM) is supplying power to the fuel pump. If there is no voltage, there may be an issue with the CCRM or a problem with the wiring between the CCRM and the inertia switch.

Additionally, ensure that the fuel pump is receiving power by listening for it to run when the key is turned to the 'on' position. If the fuel pump is not running, there may be an issue with the wiring between the inertia switch and the pump, or the pump itself may be faulty.

Further Troubleshooting

If you're still experiencing issues with fuel pressure or the car not starting, consider checking the following:

• Fuel pressure: Confirm that there is fuel pressure at the fuel rail. A lack of fuel pressure could indicate a faulty fuel pump or a problem with the fuel pressure regulator.
• Fuses: Check all fuses, including those in the fuse box and the CCRM, to ensure they are not blown.
• Modifications: If your Mustang has been modified, ensure that the modifications were done correctly and are not causing any issues with the fuel system or electrical wiring.
• Fuel pump wiring: If the fuel pump is receiving power but not building pressure, there may be an issue with the wiring or the fuel pump itself. Consider replacing the fuel pump or consulting a professional mechanic for further diagnosis.
• Fuel pump relay: If the fuel pump relay is clicking but the pump is not running, there could be an issue with the relay or the wiring between the relay and the pump.

By systematically checking these factors, you can narrow down the potential causes of low fuel pressure or starting issues in your 1999 Mustang V6.

Check the fuse in the engine compartment fuse box.

To check the fuse in the engine compartment fuse box of your 1999 Mustang V6, you'll first need to locate the fuse box. The engine compartment fuse box is located under the hood of your car, and it contains many of the high-amp fuses needed to run the engine.

Once you've located the engine compartment fuse box, you can follow these steps to check the fuse:

• Identify the fuse: In the case of the fuel pump, the fuse is labeled "Fuel Pump" and is located in the engine compartment fuse and relay box.
• Check if the fuse is blown: You can use a fuse tester, which typically costs less than $10 and includes spare fuses. Insert the tester into the fuse to check if it is still passing current. If the light on the tester glows, the fuse is intact. If not, the fuse is blown and needs to be replaced.
• Examine the fuse: If the tester indicates a blown fuse, you can use a fuse puller (often included in the fuse box) or tweezers to remove the fuse for further inspection.
• Replace the fuse: If the fuse appears damaged or blown, replace it with a new one of the same amperage. Ensure that you refer to the fuse roadmap or your owner's manual to identify the correct amperage and location for the replacement fuse.
• Check for other issues: If replacing the fuse does not resolve the issue, you may need to check for a short circuit or a wiring problem.

By following these steps, you can ensure that the fuse in the engine compartment fuse box of your 1999 Mustang V6 is functioning properly.

Check the Constant Control Relay Module (CCRM).

The Constant Control Relay Module (CCRM) is a component found in the 1994-2004 SN95 Mustang that provides power to the powertrain control module (PCM) for various components. These include the fuel pump driver module (FPDM), the cooling fan, the air conditioner compressor clutch, and the fuel pump. If any of these components are not receiving power, the CCRM may be faulty.

To check the CCRM, first locate it based on the model and year of your Mustang. For 1996-2004 models, the CCRM is on the inner fender of the passenger side, and you'll need to remove the wheel and inner fender liner to access it. On 1994-1995 models, the CCRM is mounted to the overfill mounting bracket in front of the radiator fan.

Once you've located the CCRM, follow these steps to test its functionality:

• Disconnect both battery cables from the battery.
• Remove the wheel and inner splash shield (for 1996-2004 models) or the overfill bracket (for 1994-1995 models) to access the CCRM.
• Using a 5mm socket, remove the wiring harness connection from the CCRM.
• Pull the wiring harness away from the module to completely detach it.
• Remove the two 5.5mm bolts that secure the CCRM to the mounting bracket.
• Carefully take the CCRM out of the bracket.
• Inspect the CCRM for any visible signs of damage, such as burnt or corroded connectors.
• Use a multimeter to test the continuity of the CCRM circuits. Compare the readings with the schematic diagram to identify any faulty or malfunctioning circuits.
• If the CCRM is faulty, replace it with a new one, ensuring that the part number matches your Mustang's model and year.

It's important to note that the CCRM for V6 and V8 engines are different, and the 2001-2004 CCRM is also different from the older 1994-2000 version. Always double-check the part number when installing a replacement CCRM.

Check the fuel filter and fuel tank level.

To check the fuel filter and fuel tank level on a 1999 Mustang V6, follow these steps:

First, locate the fuel filter. In a 1999 Mustang, the fuel filter is located in front of the rear axle, above and to the front of the rear differential. To access it, you may need to lift the car high enough to crawl under it and remove the old fuel filter.

Before removing the fuel filter, it is important to depressurize the fuel system. The Mustang has an inertia switch in the trunk on the driver's side that can be used to do this. Open the panel by undoing the plastic connector, pull back the liner, and locate the switch. With the car running, unplug the inertia switch connector. The car will run for a few seconds and then shut off, depressurizing the fuel system.

Now, you can proceed to remove the old fuel filter. Start by removing the two plastic end covers and then undo the screw securing the filter. Be sure to wear gloves and eye protection and have a rag handy to soak up any gasoline that may drip out. Use a fuel line disconnect tool to disconnect the fuel lines from both sides of the filter.

Once the fuel lines are disconnected, pull out the old fuel filter and inspect it. If it is clogged or discoloured, it may be due for replacement. Install a new fuel filter, if necessary, ensuring that it is installed in the correct direction. The new filter should have an arrow indicating the direction of fuel flow.

To check the fuel tank level, you can refer to the fuel gauge on your dashboard. If the gauge is not working properly, there may be an issue with the fuel level sensor or the stepper motor in the gauge cluster. In this case, you may need to consult a mechanic or a specialist to diagnose and resolve the issue.

Check the fuel pump.

To check the fuel pump of your '99 Mustang V6, you can start by locating the fuel pump relay. This is usually found in the engine bay, near the fuse box. With the key in the "on" position, you can check for power at the relay using a multimeter. If there is power, the next step is to check for voltage at the fuel pump itself. This can be done by disconnecting the electrical connector at the fuel tank and measuring the voltage. If there is no voltage, there may be an issue with the wiring between the relay and the pump.

If the fuel pump is not running, it may need to be replaced. However, before replacing the pump, it is recommended to check the fuel filter and the fuses, relays, and switches associated with the fuel system. It is also worth noting that some Mustang models have an inertia switch or a fuel pump reset switch, which can be checked to ensure it is not tripped. Additionally, issues with the fuel pump wiring or other components, such as the FRPS (Fuel Rail Pressure Sensor), may be causing the problem.

If you are experiencing issues with your fuel pump, it is important to thoroughly diagnose the problem by checking all related components and wiring. This will help ensure that the correct part is replaced and prevent unnecessary repairs or costs.

Frequently asked questions