Fuel System Diagnosis: Notes

NOTE: Wrap a shop towel around the fuel pressure tap to absorb any small amount of fuel leakage that may occur when installing the gauge. FUEL SYSTEM DIAGNOSTIC charts can be found following the TROUBLE SHOOTING section. See Figure -Figure .

Connect Fuel Pressure Gauge (J-34730 1) to fuel system. Turn ignition on. Fuel pump pressure should be 37-43 psi (2.6-3.0 kg/cm² ). This pressure is controlled by spring pressure within the regulator assembly.
When the engine is idling, the manifold pressure is low (high vacuum) and is applied to the fuel regulator diaphragm. This will offset the spring and result in a lower fuel pressure of 35-38 psi (2.5-2.7 kg/cm² ).
The idle pressure will vary depending on barometric pressure. If the pressure at idle is less than 35 psi (2.5 kg/cm² ) this indicates a problem with the pressure regulator control.
If fuel is observed in vacuum hose to pressure regulator, the regulator is faulty and must be replaced. Pressure that continues to fall is caused by 1 of the following: In-tank fuel pump check valve not holding, pump coupling hose leaking, fuel pressure regulator valve leaking or a injector sticking open.
If regulated pressure is less than 37 psi (2.6 kg/cm² ), the amount of fuel to the injectors is okay but pressure is too low. System will be lean running and may set code 44 and also cause hard starting cold and overall poor performance.