The Fuel Management Unit (Part 2 of 2)
The FMU and vehicle fuel systems were explained in the first part of this series (The Fuel Management Unit - Part 1 of 2). In this segment we will go deeper in to the FMU and its ability to support horsepower.
The FMU, also know as a “boost dependent fuel pressure regulator,” only increases fuel rail pressure when boost is applied to the reference port on the FMU. This regulator is in the return fuel line and is downstream of the static fuel pressure regulator. The FMU is a simple mechanical device that can be calibrated by changing the internal ring and spacer. Inside an FMU is a piston. The boost pressure comes from the manifold to a fitting on the FMU and applies pressure to a washer sitting on the piston. The larger the washer, the more pressure it applies on the piston. The piston pressure blocks the flow of fuel down the return line. This backup creates a higher line pressure because the fuel cannot freely pass through.
As explained in the previous article, there are two key ingredients to making horsepower: fuel and air. We are going to discuss the most popular methods of increasing the quantity of fuel, to support the air entering the motor under boost, and its relationship to the amount of power you are trying to make.
Steps to Delivering More Fuel
Upgrade Your Injector Scenario
To get more fuel, you can run larger injectors, increase the pressure to the injectors you already have, or add an auxiliary set of injectors. The auxiliary set of injectors usually squirts fuel into the manifold and requires a secondary injector driver to tell the injectors when to fire and for how long. This method is effective for street cars because it lets the car run like normal with smaller injectors. It is also good for cruising because it prevents the motor from overloading with fuel and stumbling. It then allows the second set of larger injectors to give more fuel when you are trying to make power. The major downside is that this method is very expensive because of the additional components required. Furthermore, it can be very difficult to tune because of the wide adjustment range of a completely separate set of injectors. This common dilemma led to the eventual creation of the FMU.
the Power of the FMU
Programs and Fuel Management
specific information about FMU system, start with our Feature
FMU page and select an application.