Chart A-7, Fuel Pressure Test

The fuel pump will deliver fuel to fuel rail and injectors and then to pressure regulator, where system pressure is controlled. Excess fuel pressure is by-passed back to fuel tank. The fuel pump test terminal is located in the engine compartment. Fuel pump can be turned on by applying battery voltage to test terminal.

Improper fuel system pressure may contribute to one or all of the following symptoms:

• Cranks but won't run.
• Code 44 or 45.

1. Disconnect negative battery terminal to avoid possible fuel discharge if an accidental attempt is made to start engine.
2. Loosen filler cap in order to relieve tank vapor pressure.
3. Install Fuel Pressure Gauge (J-34730-1) to pressure tap. Wrap a shop towel around fuel pressure gauge tap to absorb any small amount of fuel leakage that may occur when installing gauge.
4. Install bleed hose into an approved container and open valve to bleed system pressure. Fuel connections are now safe for servicing.
5. Drain any fuel remaining in gauge, into an approved container.
   NOTE: Test numbers refer to test numbers on diagnostic chart.

1. Start engine. With ignition on and engine running, pump pressure is regulated by spring pressure and throttle body vacuum within pressure regulator assembly. Turn ignition off for 10 seconds. Pressure should not leak down after fuel pump is shut off.
2. When engine is idling, vacuum is high and is applied to fuel pressure regulator diaphragm. This will overcome regulator spring pressure, resulting in a lower fuel pressure.
3. The application of 12-14 in. Hg vacuum to pressure regulator should result in reduced fuel pressure.
4. Fuel pressure that leaks down may be caused by one of the following conditions:
   • In-tank fuel pump check valve not holding.
   • Pump coupling hose leaking.
   • Fuel pressure regulator valve leaking.
   • Injector sticking open.
     Fig 1: Chart A-7, Flow Chart Fuel Pressure Test (1 of 2)

     

   Improper fuel system pressure may contribute to one or all of the following symptoms:

   • Cranks but won't run.
   • Code EO44 or EO45.
   • Cuts out, may feel like ignition problem.
   • Cuts out, may feel like ignition problem.
   • Hesitation, loss of power or poor fuel economy.

5. If fuel system has pressure, but is less than specification, condition may be caused by one of the following:
   • Regulated pressure, but less than specification. The amount of fuel to injectors is okay, but pressure is too low. The fuel system will operate lean and may set Code EO44. Also, hard starting cold and overall poor performance condition may exist.
   • Restricted fuel flow causing pressure drop. Normally, vehicle with fuel pressure of less than 24 psi (1.7 kg/cm² ) at idle will not be driveable. If pressure drop occurs only while driving, engine will normally surge and shut off as pressure begins to drop rapidly.
6. Restricting fuel return line allows fuel pump to develop its maximum pressure (dead head pressure). When battery voltage is applied to pump test terminal, pressure should be greater than 75 psi (5.2 kg/cm² ).
7. This test determines if high fuel pressure is due to a restricted fuel return line or a pressure regulator problem.
   Fig 2: Chart A-7, Flow Chart Fuel Pressure Test (2 of 2)