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Fuel Pressure Regulator
Contributed By: SDSEFI Basic Operation
EFI fuel pressure regulators come in various shapes and sizes but their purpose is the same- to hold the fuel pressure at a certain differential above the intake manifold pressure. The inner mechanism usually consists of a sealed diaphram chamber, a spring, a diaphram, bypass valve and a manifold pressure reference port. The valve is connected to the diaphram and the spring pushes against the diaphram from the manifold pressure side. The spring pressure determines the static fuel pressure. If there is vacuum on the port, say at idle, this reduces the effective spring pressure acting on the diaphram and reduces the fuel pressure under vacuum conditions. If there is pressure on the port, such as under boost, this effectively increases the spring pressure, thus fuel pressure.
Most OE regulators use a one to one ratio. At one psi of boost, it would add one psi of fuel pressure. This way there is always a constant pressure differential across the fuel injector. Most regulators have a static pressure of between 38 and 44 psi. The fuel pump always puts out an excess of fuel volume. The regulator controls the pressure in the fuel rail by bypassing any fuel not used by the engine back to the fuel tank once the control pressure is met. At idle, perhaps 95% of the fuel delivered to the fuel rail is returned to the tank. At full power, perhaps 5% to 50% of the fuel delivered is returned back to the tank. Fuel is generally routed from the pump to one end of the fuel rail which feeds the injectors. The regulator is usually mounted on the opposite end of the rail. This arrangement allows any hot fuel in the rail to be immediately purged back to the tank after a hot start to reduce vapor lock and fuel boiling. A similar arrangement should be used if you are fabricating your own fuel system.
Contributed By: SDSEFI Basic Operation
EFI fuel pressure regulators come in various shapes and sizes but their purpose is the same- to hold the fuel pressure at a certain differential above the intake manifold pressure. The inner mechanism usually consists of a sealed diaphram chamber, a spring, a diaphram, bypass valve and a manifold pressure reference port. The valve is connected to the diaphram and the spring pushes against the diaphram from the manifold pressure side. The spring pressure determines the static fuel pressure. If there is vacuum on the port, say at idle, this reduces the effective spring pressure acting on the diaphram and reduces the fuel pressure under vacuum conditions. If there is pressure on the port, such as under boost, this effectively increases the spring pressure, thus fuel pressure.
Most OE regulators use a one to one ratio. At one psi of boost, it would add one psi of fuel pressure. This way there is always a constant pressure differential across the fuel injector. Most regulators have a static pressure of between 38 and 44 psi. The fuel pump always puts out an excess of fuel volume. The regulator controls the pressure in the fuel rail by bypassing any fuel not used by the engine back to the fuel tank once the control pressure is met. At idle, perhaps 95% of the fuel delivered to the fuel rail is returned to the tank. At full power, perhaps 5% to 50% of the fuel delivered is returned back to the tank. Fuel is generally routed from the pump to one end of the fuel rail which feeds the injectors. The regulator is usually mounted on the opposite end of the rail. This arrangement allows any hot fuel in the rail to be immediately purged back to the tank after a hot start to reduce vapor lock and fuel boiling. A similar arrangement should be used if you are fabricating your own fuel system.
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