The fuel system in the 1999 Ford Mustang is a return-less system that uses a fuel pump module to supply and modulate power to the pump and vary the speed at which the pump runs. Testing the fuel pump in this Mustang is similar to testing older Mustangs, with the exception of adding a fuel pressure regulator test. The average home mechanic can test this system in a few minutes.
Place wedge-shaped wheel chocks behind and in front of the front wheels of the Mustang. Kick the wheel chocks with your heel to force them securely against the tire, preventing the car from rolling.
Raise the rear wheels of the car off the ground using a floor jack placed under the center of the (differential) housing in the rear of the car. Place jack stands under both rear axle tubes that connect the rear wheels to the differential. Lower the jack until the axle tubes are resting on the stands.
Attach the battery clips on the automotive circuit tester to the Mustang's battery located in the driver-side front of the engine compartment. To do this, squeeze the insulated portion of the clip to spread its spring loaded metal jaws and slip the open jaws over the battery terminal. Release the clip.
Turn the ignition key to the "RUN" position and test the fuel pump fuse in the under-hood fuse block by touching the long, sharply pointed probe end of the tester to the tiny metal test pins visible on the exposed numbered end of the fuse, protruding from the fuse block. Replace the fuse if the red light on the tester comes on indicating power is present on one test pin and the green light on the tester comes on indicating ground is present on the other test pin.
Push the probe end of the tester into the back of the fuel pump's electrical connector in the cavity that contains the pink wire with a black stripe, so that the probe makes contact with the metal terminals inside the electrical connector. In the 1999 Mustang the electrical connector is under the car, in front of the fuel tank, near the fuel lines. Have a helper turn the key to the "START" position and observe the tester. Power will show by the red light on the tester.
Replace the fuel pump driver module if power is not present.
Relieve the residual fuel pressure in the system by removing the fuel pump fuse from the under-hood fuse block and starting the engine. The fuel pump fuse can be pulled out of the fuse block with a fuse puller or a small pair of needle-nose pliers but care should be taken not to crush the plastic fuse. Start the engine and allow the Mustang to idle until the engine stalls indicating the fuel pressure has been relieved.
Screw the metal end of the fuel pressure tester's hose clockwise onto the threaded test port found on the fuel rail (sometimes called a fuel manifold) that is attached to the top of the fuel injectors that are located on the intake manifold between the cylinder heads. In the 1999 Mustang the threaded test port is located on the passenger side of the fuel rail near the front of the engine.
Reinstall the fuel pump fuse by pushing it securely into the slot it came out of. Have a helper cycle the ignition key off and one three times and then try to start the engine. This will turn the fuel pump on and prime the fuel system. Observe the needle on the gauge face and note the pressure indicated by the needle's position on the gauge face's numbered scale. If the pressure is below 45 psi, replace the fuel pump assembly.
