How Do Fuel Pressure Regulators Work?

by Don Bowman

All fuel-injected vehicles have fuel pressure regulators to maintain a regulated amount of fuel flow. Fuel injectors require a set amount of pressure at the nozzle at all times while in operation. In operation, fuel injectors do not operate by increasing or decreasing the opening for fuel flow -- they simply open the same but for a longer or shorter duration, as needed.

Fuel pressure can run between 25 to 60 pounds of pressure depending on the vehicle and manufacturer. All vehicles will have the regulator on the fuel rail containing the fuel injectors. There is a main fuel line from the fuel tank to the fuel rail and a return fuel line from the fuel pressure regulator. This return line is located downstream of all the injectors. The fuel pressure regulator uses a diaphragm and spring combination within its housing with a vacuum source on the top side of the diaphragm to counteract the spring pressure when high demand dictates that higher fuel pressure is necessary.

The computer uses sensors to determine everything from air density, air temperature, temperature of the engine, load on the engine and position of the throttle, to mention a few. The computer takes this information and decides on a strategy to get the best performance out of the engine in terms of power, fuel economy and emissions. One of these strategies is to determine how long to keep the fuel injectors on to maintain a mixture ratio of 14.5 to 1. To maintain this fuel ratio, the pressure must be maintained within one pound of pressure.

When the engine is suddenly under heavy acceleration, the vacuum drops off momentarily and then recovers within a very short period of time. This sudden drop in pressure during acceleration also affects the fuel pressure, as the injectors are suddenly opened longer. The fuel pump takes a second to catch up with the pressure, so the fuel pressure regulator reacts to the drop in vacuum by closing the fuel return line momentarily. This gives a momentary boost in fuel pressure.

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