Chart A-7, Fuel System Pressure Test: Notes

Fuel pump delivers fuel to the fuel rail and injectors, where the system pressure is controlled from 35-38 psi (262-303 kPa) by pressure regulator. Excess fuel is returned to the fuel tank. When engine is stopped, the pump can be energized by applying battery voltage to the test terminal located in engine compartment.

1. Use Pressure Gauge (J 34730-1). Wrap a shop towel around fuel pressure tap to absorb any small of fuel leakage that may occur when installing gage. Fuel pressure will not bleed down after fuel pump is off.
2. While engine is idling, manifold pressure is low (vacuum). When applied to fuel regulator diaphragm, pressure will result in a lower fuel pressure of about 30-35 psi (207-241 kPa).
3. The application of vacuum to pressure regulator should result in a fuel pressure drop.
4. Pressure leak-down may be caused by one of the following:
   • In-tank fuel pump check valve not holding
   • Pump coupling hose leaking
   • Fuel pressure regulator valve leaking
   • Injector sticking open
5. Pressure less than 38 psi (262 kPa) may be caused by one of the 2 following problems:
   • Regulated fuel pressure is too low. The system will be running lean and may set Code 25. Also hard starting cold and overall poor performance is possible.
   • Restricted flow is causing a pressure drop. Normally, a vehicle with a fuel pressure loss at idle will not be driveable. However, if pressure drop occurs only while driving, the engine will surge and stop as pressure begins to drop rapidly.
6. Restricting fuel return line allows fuel pump to build above regulated pressure. When battery voltage is applied to "Fp" on the check connector, pressure should be above 65 psi (450 kPa).
7. This test determines if high fuel pressure is due to restricted fuel return line or pressure regulator problem.