This blog post discusses what a Fuel Pump Controller is, what it does, and how it works. If you want to diagnose a fuel pump controller issue (P0230), please take a look at part 2 by clicking here.
What is a Fuel Pump Controller?
The Fuel Pump Controller is a module found on USDM turbo Subarus from 2002 to now. There are two varieties, one for the EJ platform and one for the FA platform. The job of the fuel pump controller is to regulate how hard the fuel pump works, which determines how much fuel the engine gets. This adjustment has three different settings, low, medium, and high. This part is because the fuel required while idling or otherwise being in vacuum is much less than when in boost for turbo engines. If fuel were pushing into the fuel lines at maximum flow all the time, the fuel pressure regulator would not be able to keep appropriate pressure. When the engine doesn't need the fuel, the fuel lines become over-pressured, which causes all sorts of issues with the fuel system.
Better Fuel Economy
With the pump regulation, the fuel sent to the engine is less overall, primarily if the car is driven while out of boost. Obviously, if your foot is always on the floor, that would negate this benefit.
The pump is spending less time at full speed, so the life span of the pump is increased. Mechanical components last longer when they are not being pushed to their limit at all times.
Lower Fuel Temperatures
If less fuel is being pushed through the system and returned, it doesn't have an opportunity to heat up while it passes through the fuel system in the engine bay. The cooler the fuel, the more power the engine can make.
The ECU is in control of what the fuel pump controller is doing. Beyond the low, medium, and high settings, it controls on and off. If the engine does not detect the engine rotating, the ECU will turn off the pump. This is especially important if the worst-case scenario of an accident. The last thing anyone would want is the pump flowing and fueling a fire.
How does it work
EJ Platform Fuel Pump Controllers
Like most things Subaru, the EJ fuel pump controller regulates the fuel pump's speed on the circuit's ground side. A consistent 12v signal flows through the controller. Meanwhile, the controller uses pulse width modulation (PWM) for cycling the ground side on at off at different intervals to control the speed of the pump. So the shorter the duration of the off time, the faster the pump will spin.
Low = 33% (7v-8v when testing)
Medium = 66% (9v-10v when testing)
High = 100% (12v+ when testing)
The fuel pump controller also regulates the output for the fuel pump to keep it consistently at 12v. As you modify the car and need more fuel, that can be a limiting factor. This is why we developed our plug-and-play fuel pump hardwire kit. More about these kits can be found by clicking here.
FA Platform Fuel Pump Controllers
The FA platform approaches the fuel pump controller differently because the engine is Direct-Injected. A high-pressure pump is integrated into the engine side to collect the fuel and deliver it at extremely high pressures (over 3,000 PSI). This means the in-tank fuel pump acts more like a lift pump to feed the engine.
Instead of regulating the fuel pump on the ground side, it works on the power side. This means hardwiring the pump is not possible with the stock controller. This controller is also much smaller than the EJ platform with diminished heat sinks, so it's likely as the pumps get larger to keep up with the high-pressure pump, it will fail much sooner than the EJ controllers. We are working on a solution to this problem currently.
This controller also has low, medium, and high settings, but the range is much tighter and at the higher end of the duty cycle.
Low = 75%
Medium = 79%
High = 89%.
Engine Swaps from non-turbo to turbo platformsNon-turbo platforms (except for 6-cylinder) do not use a fuel pump controller because they don't have a wide variation of fuel requirements. An appropriately sized pump for the application can flow at a consistent rate without causing issues.
When swapping a car, the fuel pump controller must be added since the non-turbo car didn't have one from the factory. This is important to add because of the issues noted above, like fuel pressure, fuel temperature, and for safety reasons.