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Circuit Description :
When the fuel pump is running, fuel is delivered to the injector(s) and then to the regulator where the system pressure is controlled to about 62 to 90 kPa (9 to 13 psi). Excess fuel is then returned to the fuel tank.

Test Description : Numbers below refer to circled numbers on the diagnostic chart.
Pressure but less than 62 kPa (9 psi) falls into two areas:
Regulated pressure but less than 62 kPa (9 psi) - Amount of fuel to injector OK but pressure is too low. System will be lean running and may set Code 44. Also, hard starting cold and poor overall performance.
Restricted flow causing pressure drop - Normally, a vehicle with a fuel pressure of less than 62 kPa (9 psi) at idle will not be driveable. However, if the pressure drop occurs only while driving, the engine will normally surge then stop as pressure begins to drop rapidly.
Restricting the fuel return line allows the fuel pump to develop its maximum pressure (dead head pressure). When battery voltage is applied to the pump test connector, pressure should be from 90 to 124 kPa (13 to 18 psi).
This test determines if the high fuel pressure is due to a restricted fuel return line or a throttle body pressure regulator problem.
Diagnostic Aids :
If the vehicle is equipped with a fuel module, the module must be disconnected before performing the fuel system pressure test.
Fuel system is under pressure.
On V6 or V8 engine, the fuel pressure drops to almost zero psi after pump shuts "off".


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