Part 1 of 2

Chart A-7 (Part 1 Of 2) Fuel Pressure Test:

Circuit Description
The fuel pump delivers fuel to the fuel rail and injectors, where the system pressure is controlled from 280 to 320 kPa (41 to 46 psi) by the fuel pressure control valve. Excess fuel is returned to the fuel tank. When the engine is stopped, the pump can be energized by jumping the fuel pump relay connector with a fused jumper.

Test Description
Numbers below refer to circled numbers on the diagnostic chart.
1. Use pressure gauge J-34730-1. Wrap a shop towel around the fuel pressure tap to absorb any small amount of fuel leakage that may occur when installing the gauge. (The pressure will not leak down after the fuel pump is stopped on a correctly functioning system.)
2. While the engine is idling, manifold absolute pressure is low (high vacuum). When this is applied to the fuel regulator diaphragm the vacuum will result in a lower fuel pressure at about 190- 200 kPa (25 - 30 psi)
3. The application of high vacuum to the fuel pressure control valve should result in a fuel pressure drop.
4. Fuel pressure leak-down may be caused by one of the following:
^ Fuel pump check valve not holding.
^ Pump coupling hose leaking.
^ Fuel pressure control valve leaking.
^ Injector sticking open/leaking.

Diagnostic Aids
Improper fuel system pressure may contribute to one or all of the following symptoms:
^ Cranks but will not run.
^ Diagnostic trouble code 44 or 45.
^ Cutting out (May feel like ignition problem).
^ Hesitation, loss of power or poor fuel economy.