Test Description
The numbers below refer to the step numbers in the diagnostic procedure.
- 2
Wrap a shop towel around the fuel pressure connection to absorb any small amount of fuel leakage that may occur when installing the fuel pressure gauge. Turn ON the ignition leaving the engine OFF, the fuel pressure should be 60-66 psi (415-455 kPa) when the pump is running. This pressure is controlled by a spring pressure within the regulator assembly. - 4
The fuel pressure that continues to fall is caused by one of the following items:- The in-tank modular fuel sender is not holding pressure.
- The fuel pressure regulator valve is leaking.
- A Central SFI injector is leaking.
- Fuel line is leaking.
- 15
If the fuel pressure is less than 55 psi (379 kPa) at idle, it falls into the following 3 areas:- The pressure is regulated but less than 55 psi (379 kPa). The amount of fuel reaching the injector is sufficient, but the pressure is too low. The system will run lean, hard starting cold, no start, overall poor performance, and may set a DTC. See NO-START DIAGNOSIS .
- A restricted flow causing pressure drop. Normally, a vehicle with a fuel pressure of less than 44 psi (300 kPa) at idle is inoperable. However, if the pressure drop occurs only while driving, the engine will normally surge then stop running as the pressure begins to drop rapidly. This is most likely caused by a restricted fuel line or plugged fuel filter.
- A leaking or contaminated pressure regulator valve or seat interface may not allow the regulated pressure to be achieved.
- 21
DO NOT allow the fuel pressure to exceed 75 psi (517 kPa). Excessive pressure may damage the fuel system. Restricting the fuel return line allows the fuel pressure to build above regulated pressure. With the fuel pump commanded ON, the fuel pressure should rise above 66 psi (455 kPa), as the valve in the return line is partially closed. - 26
When the engine is idling, the manifold pressure is low (high vacuum) and is applied to the fuel pressure regulator diaphragm. This will offset the spring and result in a lower fuel pressure. This idle pressure will vary somewhat depending on the barometric pressure. However, the pressure at idle should be less, indicating the pressure regulator control. - 29
If the injector(s) is not grounded, physically remove suspect injector(s) and inspect for a fuel leak while system is pressurized. If the fuel injector(s) are not leaking and fuel pressure is not holding, the fuel pressure regulator should be inspected for a slow diaphragm leak.