Chart A-7 - Fuel System Pressure Test: Notes
NOTE:
Test numbers refer to numbers on diagnostic chart.
- Use Pressure Gauge (J-34730-1) and Adapter (J-35957-10) . Wrap shop towel around fuel pressure fitting to absorb any fuel leakage when installing gauge. On correctly functioning system, fuel pressure will not leak down when ignition is off.
- Manifold vacuum pressure is low when engine is idling. When vacuum is applied to fuel pressure regulator diaphragm, fuel pressure will drop to approximately 25-30 psi (1.8-2.1 kg/cm2 ).
- Applying vacuum to pressure regulator should cause fuel pressure to drop slightly.
- 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
- Injector Stuck Open
- Pressure less than 35 psi (2.5 kg/cm2
) may be caused by one of the following:
- Regulated fuel pressure is too low. System will be running lean and may set Code 44. Hard cold starting and overall poor performance is possible.
- Restricted flow is causing a pressure drop. Vehicle with fuel pressure drop at idle is usually not driveable. Fuel pressure drop while driving will cause engine to surge and possibly stop as pressure rapidly drops.
- Restricting fuel return line when battery voltage is applied to fuel pump allows fuel pump to build over regulated pressure. Pressure should be 65 psi (4.5 kg/cm2 ) or greater.
- This determines if high fuel pressure is due to restricted fuel line or a pressure regulator problem.