Fuel pumps typically operate by pressurizing the fuel line to create a vacuum, which pulls fuel from the fuel tank into the engine. The 1987 Ford Bronco II uses two fuel pumps: a low-pressure pump located inside the fuel tank and a high-pressure pump attached to the fuel line and bolted to the frame about midway up the body. Troubleshooting the fuel pump requires locating the diagnostic pressure valve (Schrader valve) located on the fuel supply manifold along the rail.
Locate the Schrader valve. The valve is located on the fuel supply manifold (rail) on the engine itself. To easily locate, trace the fuel line into the engine. The Schrader valve looks like a metal valve stem and may have a plastic cap. Remove the plastic cap.
Attach the pressure gauge T80L-9974-B or equivalent to the Schrader valve. Purchase of the tool includes specific directions for use and interpreting the results. For simple testing of fuel pressure coming out of the fuel pump, an inexpensive pressure or vacuum gauge can be used.
Start the vehicle and monitor the pressure gauge. Pressure should be maintained between 35 and 45 PSI. Fluctuations within this range will occur. However, deviations outside of that range imply a fuel pump issue and most likely mean that you should replace the fuel pump.
