- In modern automobile engines the fuel pressure regulator (FPR) uses a spring-driven diaphragm to maintain the flow rate of fuel into a fuel injector. This injector in turn delivers the fuel to a combustion chamber within the engine. The FPR is one part of an electronic fuel injection (EFI) system, which requires a computerized engine control unit (ECU) to operate. Unlike the fuel injector, however, the FPR is expected to maintain a constant fuel pressure that does not require modulation by the ECU. Changes in the rate of fuel injection are made in the injector itself, not in the FPR.
- The goal of an EFI is to maintain an optimal rate of fuel and air mixture for complete combustion of all materials. Older cars use carburetors to control the flow of air into the ignition chamber. While having the advantage of being a single unit that performs all the functions of the (significantly more complex) EFI, carburetors inevitably lead to some inefficiency in combustion. In practice, this means that certain engine cylinders would receive excess fuel to ensure that all cylinders received enough fuel. This imbalance, if too severe or over a long enough time, leads to a loss of engine power.
- As the fuel is dispensed from the tank through the fuel rail, it is either released already pressurized or encounters a pump that adds the necessary pressure. This pressurized fuel then encounters the fuel pressure regulator, which ensures a constant pressure (usually 28 psi in personal automobiles) as the fuel continues to the fuel injector. When the fuel reaches the injector the FPR has assured that it is at a predictable and useful pressure. The injector then fires the fuel into the air stream entering the engine, premixing the two reagents and assuring near-perfect combustion when the two are ignited.
- The FPR works by a simple spring diaphragm connected to a valve. When the diaphragm becomes sufficiently loaded by pressure in the fuel line it opens a separate line that shunts excess fuel back to the tank. FPRs are rarely the cause of engine problems due to their simplicity and durability of basic design.
