When the injectors and fuel pump are upgraded to a larger flow setup the stock fuel pressure regulator will not be enough to suit the required pressures for the new setup. Also the stock is already preset to from factory for the standard setup and non adjustable so it will be restricting the tuning potential of the car. The TOMEI Fuel Pressure Regulator will ensure stable pressures are supplied with the oversized diaphragm. This special design has proven to maintain the required pressure levels with any adjustments made.
When the engine is idling low the fuel flow used compared to full power is only approx 15%. Therefore most of the fuel that is sent by the pump will be returned to the fuel tank. When the engine is tuned the optimum efficiency can be obtained with the optimum mixture of A/F ratio. When the fuel pump is too large and the regulator is not strong enough to handle the excess fuel that it is receiving it will then not be able to regulate the flow to allow the fuel to return to the tank. This will cause the fuel pressure to be too high and too much fuel to be pumped into the engine which will lead to over enrichment and poor fuel efficiency and a variety of problems will occur.