CHART A-7, FUEL SYSTEM PRESSURE TEST (GSi): Notes

Fuel pump delivers fuel to fuel rail and fuel injectors with fuel pressure maintained at 38-44 psi (2.7-3.1 kg/cm² ) by pressure regulator. Excess fuel is returned to fuel tank. With engine stopped, fuel pump can be energized by applying battery voltage to check connector located in engine compartment, on left strut tower. With engine off, fuel pressure should remain greater than 21 psi (1.5 kg/cm² ) for 5 minutes.

1. Use Pressure Gauge (J-34730-1). Wrap shop towel around fuel pressure tap to absorb fuel leakage when installing gauge. Pressure should not leak down after fuel pump is stopped if system is functioning correctly.
2. With engine idling, manifold pressure (vacuum) is high and, when applied to fuel pressure regulator diaphragm, will result in a lower fuel pressure of about 30-35 psi (2.1-2.5 kg/cm² ).
3. The application of vacuum to fuel pressure regulator should result in 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 or injector sticking open.
5. Fuel pressure of less than 38 psi (2.7 kg/cm² ) may be caused by:
   • Regulated pressure too low. The system will be running lean and may set Code 25. Hard starting and overall poor performance is possible.
   • Restricted fuel flow will cause 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, engine will surge and then stop as pressure begins to drop rapidly.
6. Restricting the fuel return line allows the fuel pump to build pressure greater than regulated pressure. When battery voltage is applied to terminal FP on check connector, pressure should be greater than 65 psi (4.6 kg/cm² ).
7. This test determines if the high fuel pressure is due to a restricted fuel return pipe or a pressure regulator problem.