Q: Q: Fuel pressure problem

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car was running fine now it will not start put fuel pressure guage on and it will build pressure for two seconds and then goes to zero i changed the fuel pump relay the fuel pump and sock still no pressure i also pinch the supply line and return line no change have not changed fuel filter yet

My car has 100000 miles.
My car has an automatic transmission.

Hello, It sounds like you may possibly have a bad fuel pressure regulator. I would recommend starting with checking and replacing the filter if necessary as that is a bit less expensive. If this does not do the trick, I would then look to the fuel pressure regulator. The fuel pressure regulator is a device which controls the pressure of fuel supplied to the fuel injectors on an engine. This works by bleeding off a portion of the fuel flow to the injectors from the fuel pump to control the fuel pressure. Fuel is pumped from the fuel tank to the fuel rail by the fuel pump. The fuel pressure regulator is normally mounted after the fuel rail to ensure that the fuel rail has priority in fuel flow. The valve in the regulator controls the amount of fuel that is bled from the fuel rail by opening an outlet port to allow fuel to flow back into the fuel tank. All injectors need a pressure difference between the inlet and the outlet of the injector to spray fuel into the combustion chamber. This is called the base pressure. The base pressure is adjusted via the adjustment screw to suit the injectors and specific fuel pump system you are using. The adjustment screw pushes down on a spring which applies a force onto the valve. When the pressure inside the bottom chamber of the regulator exerts a high enough force on the valve to overcome the spring force and lift the valve off its seat, it allows fuel to flow through the outlet port effectively controlling the fuel pressure in the fuel rail. Since the outlet of the injector is exposed to manifold vacuum/pressure which varies depending on throttle movement, but the flow of fuel from the fuel pump is constant, the valve needs a reference to continuously change the amount of fuel bled to maintain constant fuel pressure to the injectors.

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